Edit Updated on 2019-05-20

1. Basic Conversations and Messages

Introduction

A lot of products today have the needs to offer instant messaging functions to their users. For example:

To have the staff behind the product talk to the users.
To have the workers in a company communicate with each other.
To have the audience of live-streamed contents interact with each other.
To have the users of an app or players of a game chat with each other.

Based on the hierarchy of needs and the difficulty of implementation, we wrote four chapters of documentation for you to learn how you can embed LeanMessage into your app:

In this chapter, we will introduce how you can implement one-on-one chatting and group chats, how you can create and join conversations, and how you can send and receive rich media messages. We will also introduce how history messages are kept on the cloud and how you can retrieve them. By the end of this chapter, you should be able to build a simple chatting page in your app.
In the second chapter, we will introduce some advanced features built around messaging, including mentioning people with "@", recalling messages, editing messages, getting receipts when messages are delivered and read, sending push notifications, and synchronizing messages. The implementation of multi device sign-on and custom message types will also be covered. By the end of this chapter, you should be able to integrate a chatting component into your app with these features.
In the third chapter, we will introduce the security features offered by our services, including third-party signing mechanism, permission management of members, and blacklisting. We will also go over the usage of chat rooms and temporary conversations. By the end of this chapter, you will get a set of skills to improve the security and usability of your app, as well as to build conversations that serve different purposes.
In the last chapter, we will introduce the usage of hooks and system conversations, plus how you can build your own chatbots based on them. By the end of this chapter, you will learn how you can make your app extensible and adapted to a wide variety of requirements.

We aim our documentation to not only help you complete the functions you are currently building but also give you a better understanding of all the things LeanMessage can do (which you will find helpful when you plan to add more features into your app).

Before you continue:

Take a look at LeanMessage Overview if you haven't done it yet. Also make sure you have already followed SDK Installation to install and initialize the SDK for the platform (language) you are using.

One-on-One Chatting

Before diving into the main topic, let's see what an IMClient object is in LeanMessage SDK:

An IMClient refers to an actual user, meaning that the user logged in to the system as a client.

See LeanMessage Overview for more details.

Creating `IMClient`

Assuming that there is a user named "Tom". Now let's create an IMClient instance for him:

var realtime = new Realtime({
  appId: 'your-app-id',
  appKey: 'your-app-key',
  plugins: [TypedMessagesPlugin], // Register plugins for rich media messages
});
// Tom logs in with his name as clientId
realtime.createIMClient('Tom').then(function(tom) {
  // Successfully logged in
}).catch(console.error);

@property (nonatomic, strong) AVIMClient *tom;
// clientId is Tom
tom = [[AVIMClient alloc] initWithClientId:@"Tom"]

// clientId is Tom
AVIMClient tom = AVIMClient.getInstance("Tom");

var realtime = new AVRealtime('your-app-id','your-app-key');
var tom = await realtime.CreateClientAsync('Tom');

Keep in mind that an IMClient refers to an actual user. It should be stored globally since all the further actions done by this user will have to access it.

Logging in to the LeanMessage Server

After creating the IMClient instance for Tom, we will need to have this instance log in to the LeanMessage server. Only clients that are logged in can chat with other users and receive notifications from the cloud.

For JavaScript and C# (Unity3D) SDKs, clients will be automatically logged in when IMClient instances are created; for iOS (both Objective-C and Swift) and Android (including Java) SDKs, clients need to be logged in manually with the open method:

// Tom logs in with his name as clientId and gets the IMClient instance
realtime.createIMClient('Tom').then(function(tom) {
  // Successfully logged in
}).catch(console.error);

// Tom creates a client and logs in with his name as clientId
AVIMClient *tom = [[AVIMClient alloc] initWithClientId:@"Tom"];
// Tom logs in
[tom openWithCallback:^(BOOL succeeded, NSError *error) {
  if(succeeded) {
    // Successfully connected
  }
}];

// Tom creates a client and logs in with his name as clientId
AVIMClient tom = AVIMClient.getInstance("Tom");
// Tom logs in
tom.open(new AVIMClientCallback() {
  @Override
  public void done(AVIMClient client, AVIMException e) {
    if (e == null) {
      // Successfully connected
    }
  }
}

var realtime = new AVRealtime('your-app-id','your-app-key');
var tom = await realtime.CreateClientAsync('Tom');

Logging in with `_User`

Beside specifying a clientId within the app, you can also log in directly with a _User object after an IMClient is created. By doing so, the signing process for logging in can be skipped which helps you easily integrate LeanStorage with LeanMessage:

var AV = require('leancloud-storage');
// Log in to LeanMessage with the username and password of an AVUser
AV.User.logIn('username', 'password').then(function(user) {
  return realtime.createIMClient(user);
}).catch(console.error.bind(console));

// Log in to LeanMessage with the username and password of an AVUser
[AVUser logInWithUsernameInBackground:username password:password block:^(AVUser * _Nullable user, NSError * _Nullable error) {
    // Create a client with AVUser instance
    AVIMClient *client = [[AVIMClient alloc] initWithUser:user];
    // Open the client to connect to the cloud
    [client openWithCallback:^(BOOL succeeded, NSError * _Nullable error) {
        // Do something you like
    }];
}];

// Log in to LeanMessage with the username and password of an AVUser
AVUser.logInInBackground("username", "password", new LogInCallback<AVUser>() {
    @Override
    public void done(AVUser user, AVException e) {
        if (null != e) {
          return;
        }
        // Connect to the server
        AVIMClient client = AVIMClient.getInstance(user);
        client.open(new AVIMClientCallback() {
          @Override
          public void done(final AVIMClient avimClient, AVIMException e) {
            // Do something as you need
          }
       });
    }
});

// Not supported yet

Creating Conversations

A Conversation needs to be created before a user can chat with others.

Conversations are the carriers of messages. All the messages are sent to conversations to be delivered to the members in them.

Since Tom is already logged in, he can start chatting with other users now. If he wants to chat with Jerry, he can create a Conversation containing Jerry and himself:

// Create a conversation with Jerry
tom.CreateConversationAsync({ // tom is an IMClient instance
  // Members of the conversation include Tom (the SDK will automatically add the current user into the conversation) and Jerry
  members: ['Jerry'],
  // Name of the conversation
  name: 'Tom & Jerry',
  unique: true
}).then(/* Do something as you need */);

// Create a conversation with Jerry
[tom createConversationWithName:@"Tom & Jerry" clientIds:@[@"Jerry"] attributes:nil options:AVIMConversationOptionUnique
                       callback:^(AVIMConversation *conversation, NSError *error) {

}];

tom.createConversation(Arrays.asList("Jerry"), "Tom & Jerry", null, false, true,
    new AVIMConversationCreatedCallback() {
        @Override
        public void done(AVIMConversation conversation, AVIMException e) {
          if(e == null) {
            // Successfullly created
          }
        }
});

var tom = await realtime.CreateClientAsync('Tom');
var conversation = await tom.CreateConversationAsync("Jerry", name:"Tom & Jerry", isUnique:true);

createConversation creates a new conversation and stores it into the _Conversation table which can be found in your app's Dashboard > LeanStorage > Data. Below are the interfaces offered by different SDKs for creating conversations:

/**
 * Create a conversation
 * @param {Object} options The fields beside the following ones will be treated as custom attributes
 * @param {String[]} options.members The members of the conversation; required; include the current client by default
 * @param {String} [options.name] The name of the conversation; optional; defaults to null
 * @param {Boolean} [options.transient=false] Whether the conversation is a chat room; optional
 * @param {Boolean} [options.unique=false] Whether the conversation is unique; if it is true and an existing conversation contains the same composition of members, the existing conversation will be reused, otherwise a new conversation will be created
 * @param {Boolean} [options.tempConv=false] Whether the conversation is temporary; optional
 * @param {Integer} [options.tempConvTTL=0] Optional; if tempConv is true, the TTL of the conversation can be specified here
 * @return {Promise.<Conversation>}
 */
async createConversation({
  members: m,
  name,
  transient,
  unique,
  tempConv,
  tempConvTTL,
  // You may add more properties
});

/*!
 Create a conversation
 For one-on-one chatting, pass in a single clientId; for group chats, pass in a list of clientIds
 @param name - The name of the conversation
 @param clientIds - The list of clientIds of participants in the conversation (except the creator)
 @param callback － The callback after the conversation is created
 */
- (void)createConversationWithName:(NSString * _Nullable)name
                         clientIds:(NSArray<NSString *> *)clientIds
                          callback:(void (^)(AVIMConversation * _Nullable conversation, NSError * _Nullable error))callback;
/*!
 Create a conversation
 For one-on-one chatting, pass in a single clientId; for group chats, pass in a list of clientIds
 @param name - The name of the conversation
 @param clientIds - The list of clientIds of participants in the conversation (except the creator)
 @param attributes - Custom attributes
 @param options － Optional; multiple options can be divided by "|"
 @param callback － The callback after the conversation is created
 */
- (void)createConversationWithName:(NSString * _Nullable)name
                         clientIds:(NSArray<NSString *> *)clientIds
                        attributes:(NSDictionary * _Nullable)attributes
                           options:(AVIMConversationOption)options
                          callback:(void (^)(AVIMConversation * _Nullable conversation, NSError * _Nullable error))callback;

/**
 * Create or find an existing conversation
 *
 * @param members The members in the conversation
 * @param name The name of the conversation
 * @param attributes Custom attributes
 * @param isTransient Whether the conversation is a chat room
 * @param isUnique Whether return the existing conversation satisfying conditions
 *                 If false, create a new conversation
 *                 If true, find if there is an existing conversation satisfying conditions; if so, return the conversation, otherwise create a new conversation
 *                 If true, only members is the valid query condition
 * @param callback The callback after the conversation is created
 */
public void createConversation(final List<String> members, final String name,
    final Map<String, Object> attributes, final boolean isTransient, final boolean isUnique,
    final AVIMConversationCreatedCallback callback);
/**
 * Create a conversation
 *
 * @param members The members in the conversation
 * @param attributes Custom attributes
 * @param isTransient Whether the conversation is a chat room
 * @param callback The callback after the conversation is created
 */
public void createConversation(final List<String> members, final String name,
                               final Map<String, Object> attributes, final boolean isTransient,
                               final AVIMConversationCreatedCallback callback);
/**
 * Create a conversation
 *
 * @param conversationMembers The members in the conversation
 * @param name       The name of the conversation
 * @param attributes Custom attributes
 * @param callback   The callback after the conversation is created
 * @since 3.0
 */
public void createConversation(final List<String> conversationMembers, String name,
    final Map<String, Object> attributes, final AVIMConversationCreatedCallback callback);
/**
 * Create a conversation
 * 
 * @param conversationMembers The members in the conversation
 * @param attributes Custom attributes
 * @param callback   The callback after the conversation is created
 * @since 3.0
 */
public void createConversation(final List<String> conversationMembers,
    final Map<String, Object> attributes, final AVIMConversationCreatedCallback callback);

/// <summary>
/// Create a conversation with members.
/// </summary>
/// <returns>Return the conversation.</returns>
/// <param name="member">The member in the conversation.</param>
/// <param name="members">The list of members in the conversation.</param>
/// <param name="name">The name of the conversation.</param>
/// <param name="isSystem">Whether it is a system conversation. Note that system conversations cannot be created by clients, so the conversation will not be created if it is true here.</param>
/// <param name="isTransient">Whether the conversation is a chat room.</param>
/// <param name="isUnique">Whether the conversation is unique.</param>
/// <param name="options">Custom attributes.</param>
public Task<AVIMConversation> CreateConversationAsync(string member = null,
    IEnumerable<string> members = null,
    string name = "",
    bool isSystem = false,
    bool isTransient = false,
    bool isUnique = true,
    IDictionary<string, object> options = null);

Although SDKs for different languages/platforms share different interfaces, they take in the similar set of parameters when creating a conversation:

members: Required; includes the initial list of members in the conversation. The initiator of the conversation is included by default, so members does not have to include the clientId of the current user.
name: The name of the conversation; optional. The code above puts "Tom & Jerry" for it.
attributes: The custom attributes of the conversation; optional. The code above does not specify any attributes. If you ever specify them for your conversations, you can retrieve them later with AVIMConversation. Such attributes will be stored in the attr field of the _Conversation table.
unique/isUnique or AVIMConversationOptionUnique: Marks if the conversation is unique; optional.
- If true, the cloud will perform a query on conversations with the list of members specified. If an existing conversation contains the same members, the conversation will be returned, otherwise a new conversation will be created.
- If false, a new conversation will be created each time createConversation is called.
- If not specified, it defaults to true for Java SDK and false for others (will be changed to true in the future).
- In general, it is more reasonable that there is only one conversation existing for the same composition of members, otherwise it could be messy since multiple sets of message histories are available for the same group of people. We strongly recommend that you set unique to be true when creating conversations.
Other parameters specifying the type of the conversation; optional. For example, transient/isTransient specifies if it is a chat room, and tempConv/tempConvTTL or AVIMConversationOptionTemporary specifies if it is a temporary conversation. If nothing is specified, it will be a basic conversation. We will talk more about them later.

The built-in properties of a conversation can be retrieved once the conversation is created. For example, a globally unique ID will be created for each conversation which can be retrieved with Conversation.id. This is the field often used for querying conversations.

Sending Messages

Now that the conversation is created, Tom can start sending messages to it:

var { TextMessage } = require('leancloud-realtime');
conversation.send(new TextMessage('Get up, Jerry!')).then(function(message) {
  console.log('Tom & Jerry', 'Message sent!');
}).catch(console.error);

AVIMTextMessage *message = [AVIMTextMessage messageWithText:@"Get up, Jerry!" attributes:nil];
[conversation sendMessage:message callback:^(BOOL succeeded, NSError *error) {
  if (succeeded) {
    NSLog(@"Message sent!");
  }
}];

AVIMTextMessage msg = new AVIMTextMessage();
msg.setText("Get up, Jerry!");
// Send the message
conversation.sendMessage(msg, new AVIMConversationCallback() {
  @Override
  public void done(AVIMException e) {
    if (e == null) {
      Log.d("Tom & Jerry", "Message sent!");
    }
  }
});

var textMessage = new AVIMTextMessage("Get up, Jerry!");
await conversation.SendMessageAsync(textMessage);

Conversation#send sends a message to the conversation specified. All the other members who are online will immediately receive the message.

So how would Jerry see the message on his device?

Receiving Messages

On another device, we create an AVIMClient with Jerry as clientId and log in to the server (just as how we did for Tom):

var { Event } = require('leancloud-realtime');
// Jerry logs in
realtime.createIMClient('Jerry').then(function(jerry) {
}).catch(console.error);

jerry = [[AVIMClient alloc] initWithClientId:@"Jerry"];
[jerry openWithCallback:^(BOOL succeeded, NSError *error) {

}];

// Jerry logs in
AVIMClient jerry = AVIMClient.getInstance("Jerry");
jerry.open(new AVIMClientCallback(){
  @Override
  public void done(AVIMClient client,AVIMException e){
    if(e==null){
      // Things to do after logging in
    }
  }
});

var realtime = new AVRealtime('your-app-id','your-app-key');
var jerry = await realtime.CreateClientAsync('Jerry');

As the receiver of the message, Jerry doesn't have to create a conversation with Tom and may as well not know that Tom created a conversation with him. Jerry needs to set up a callback function to get notified for the things Tom did.

By setting up callbacks, clients will be able to handle notifications sent from the cloud. Here we focus on the following two events:

The user is invited to a conversation. At the moment Tom creates a new conversation with Jerry, Jerry will receive a notification saying something like "Tom invited you to a conversation".
A new message is delivered to a conversation the user is already in. At the moment Tom sends out the message "Get up, Jerry!", Jerry will receive a notification including the message itself as well as the context information like the conversation the message is sent to and the sender of the message.

Now let's see how clients should handle such notifications. The code below handles both "joining conversation" and "getting new message" events for Jerry:

// JS SDK responds to notifications by binding events on IMClient with callbacks

// The current user is added to a conversation
jerry.on(Event.INVITED, function invitedEventHandler(payload, conversation) {
    console.log(payload.invitedBy, conversation.id);
});

// The current user receives a message; can be handled by responding to Event.MESSAGE
jerry.on(Event.MESSAGE, function(message, conversation) {
    console.log('Message received: ' + message.text);
});

// Objective-C SDK responds to notifications with AVIMClientDelegate
jerry.delegate = self;

/*!
 The current user is added to a conversation
 @param conversation － The conversation
 @param clientId - The ID of the inviter
 */
-(void)conversation:(AVIMConversation *)conversation invitedByClientId:(NSString *)clientId{
    NSLog(@"%@", [NSString stringWithFormat:@"Current clientId (Jerry) is invited by %@ to join the conversation.",clientId]);
}

/*!
 The current user receives a message
 @param conversation － The conversation
 @param message - The content of the message
 */
- (void)conversation:(AVIMConversation *)conversation didReceiveTypedMessage:(AVIMTypedMessage *)message {
    NSLog(@"%@", message.text); // Get up, Jerry!
}

// Java/Android SDK responds to notifications with custom event handlers
public class CustomConversationEventHandler extends AVIMConversationEventHandler {
  /**
   * The current user is added to a conversation
   *
   * @param client
   * @param conversation The conversation
   * @param operator The inviter
   * @since 3.0
   */
  @Override
  public void onInvited(AVIMClient client, AVIMConversation conversation, String invitedBy) {
    // Things to do after the current clientId (Jerry) is invited to the conversation
  }
}
// Set up global conversation event handler
AVIMMessageManager.setConversationEventHandler(new CustomConversationEventHandler());

// Java/Android SDK responds to notifications with custom event handlers
public static class CustomMessageHandler extends AVIMMessageHandler{
  /**
   * Reload this method to handle message receiving
   * 
   * @param message
   * @param conversation
   * @param client
   */
   @Override
   public void onMessage(AVIMMessage message,AVIMConversation conversation,AVIMClient client){
     if(message instanceof AVIMTextMessage){
       Log.d(((AVIMTextMessage)message).getText());// Get up, Jerry!
     }
   }
 }
// Set up global message handling handler
AVIMMessageManager.registerDefaultMessageHandler(new CustomMessageHandler());

// SDK responds to notifications by binding events on IMClient with callbacks
var jerry = await realtime.CreateClientAsync("Jerry");
jerry.OnInvited += (sender, args) =>
{
  var invitedBy = args.InvitedBy;
  var conversationId = args.ConversationId;
};

private void Jerry_OnMessageReceived(object sender, AVIMMessageEventArgs e)
{
    if (e.Message is AVIMTextMessage)
    {
        var textMessage = (AVIMTextMessage)e.Message;
        // textMessage.ConversationId is the ID of the conversation
        // textMessage.TextContent is the text content of the message
        // textMessage.FromClientId is the clientId of the sender
    }
}
jerry.OnMessageReceived += Jerry_OnMessageReceived;

With the two event handling functions above, Jerry will be able to receive messages from Tom. Jerry can send messages to Tom as well, as long as Tom has the same functions on his side.

Now let's take a look at the sequence diagram showing how the first message sent from Tom to Jerry is processed:

Tom->Cloud: 1. Tom adds Jerry into the conversation
Cloud-->Jerry: 2. Sends notification: you are invited to the conversation
Jerry-->UI: 3. Loads UI
Tom->Cloud: 4. Sends message
Cloud-->Jerry: 5. Sends notification: you have a new message
Jerry-->UI: 6. Shows the message

Beside responding to notifications about new messages, clients also need to respond to those indicating the change of members in a conversation, like "XX invited XX into the conversation", "XX left the conversation", and "XX is removed by the admin". Such notifications will be delivered to clients in real time. See Summary of Event Notifications Regarding Changes of Members for more details.

Group Chats

We just discussed how we can create a conversation between two users. Now let's see how we can create a group chat with more people.

There aren't many differences between the two types of conversations and a major one would be the amount of members in them. You can either specify all the members of a group chat when creating it, or add them later after the conversation is created.

Creating Group Chats

In the previous conversation between Tom and Jerry (assuming conversation ID to be CONVERSATION_ID), if Tom wants to add Mary into the conversation, the following code can be used:

// Get the conversation with ID
tom.getConversation('CONVERSATION_ID').then(function(conversation) {
  // Invite Mary
  return conversation.add(['Mary']);
}).then(function(conversation) {
  console.log('Member added!', conversation.members);
  // The conversation now contains ['Mary', 'Tom', 'Jerry']
}).catch(console.error.bind(console));

// Get the conversation with ID
AVIMConversationQuery *query = [self.client conversationQuery];
[query getConversationById:@"CONVERSATION_ID" callback:^(AVIMConversation *conversation, NSError *error) {
    // Invite Mary
    [conversation addMembersWithClientIds:@[@"Mary"] callback:^(BOOL succeeded, NSError *error) {
        if (succeeded) {
            NSLog(@"Member added!");
        }
    }];
}];

// Get the conversation with ID
final AVIMConversation conv = client.getConversation("CONVERSATION_ID");
// Invite Mary
conv.addMembers(Arrays.asList("Mary"), new AVIMConversationCallback() {
    @Override
    public void done(AVIMException e) {
      // Member added
    }
});

// Get the conversation with ID
var conversation = await tom.GetConversationAsync("CONVERSATION_ID");
// Invite Mary
await tom.InviteAsync(conversation, "Mary");

On Jerry's side, he can add a listener for handling events regarding "new members being added". With the code below, he will be notified once Tom invites Mary to the conversation:

// A user is added to the conversation
jerry.on(Event.MEMBERS_JOINED, function membersjoinedEventHandler(payload, conversation) {
    console.log(payload.members, payload.invitedBy, conversation.id);
});

jerry.delegate = self;

#pragma mark - AVIMClientDelegate
/*!
 All members will receive a notification when a new member joins the conversation
 @param conversation － The conversation
 @param clientIds - The list of new members
 @param clientId - The ID of the inviter
 */
- (void)conversation:(AVIMConversation *)conversation membersAdded:(NSArray *)clientIds byClientId:(NSString *)clientId {
    NSLog(@"%@", [NSString stringWithFormat:@"%@ is added to the conversation by %@",[clientIds objectAtIndex:0],clientId]);
}

public class CustomConversationEventHandler extends AVIMConversationEventHandler {
  /**
   * All members will receive a notification when a new member joins the conversation
   *
   * @param client
   * @param conversation
   * @param members The list of new members
   * @param invitedBy The ID of the inviter; could be the new member itself
   * @since 3.0
   */
    @Override
    public void onMemberJoined(AVIMClient client, AVIMConversation conversation,
        List<String> members, String invitedBy) {
        // Shows that Mary is added to 551260efe4b01608686c3e0f by Tom
        Toast.makeText(AVOSCloud.applicationContext,
          members + " is added to " + conversation.getConversationId() + " by "
              + invitedBy, Toast.LENGTH_SHORT).show();
    }
}
// Set up global event handler
AVIMMessageManager.setConversationEventHandler(new CustomConversationEventHandler());

private void OnMembersJoined(object sender, AVIMOnInvitedEventArgs e)
{
    // e.InvitedBy is the inviter; e.ConversationId is the ID of the conversation
    Debug.Log(string.Format("{0} invited {1} to the conversation {2}", e.InvitedBy,e.JoinedMembers, e.ConversationId));
}
jerry.OnMembersJoined += OnMembersJoined;

payload contains the following fields:

members: Array of strings; the list of clientIds of the members being added
invitedBy: String; the clientId of the inviter

AVIMOnInvitedEventArgs contains the following fields:

InvitedBy: The inviter
JoinedMembers: The list of members being added
ConversationId: The conversation

Here is the sequence diagram of the operation:

Tom->Cloud: 1. Adds Mary
Cloud->Tom: 2. Sends notification: you invited Mary to the conversation
Cloud-->Mary: 2. Sends notification: you are added to the conversation by Tom
Cloud-->Jerry: 2. Sends notification: Mary is added to the conversation by Tom

On Mary's side, to know that she is added to the conversation between Tom and Jerry, she can follow the way Jerry listens to the INVITED event, which can be found in One-on-One Chatting.

If Tom wants to create a new conversation with all the members included, the following code can be used:

tom.createConversation({
  // Add Jerry and Mary to the conversation when creating it; more members can be added later as well
  members: ['Jerry','Mary'],
  // The name of the conversation
  name: 'Tom & Jerry & friends',
  unique: true,
}).catch(console.error);

// Tom creates a conversation with his friends
NSArray *friends = @[@"Jerry", @"Mary"];
[tom createConversationWithName:@"Tom & Jerry & friends" clientIds:friends
  options:AVIMConversationOptionUnique
  callback:^(AVIMConversation *conversation, NSError *error) {
    if (!error) {
        NSLog(@"Conversation created!");
    }
}];

tom.createConversation(Arrays.asList("Jerry","Mary"), "Tom & Jerry & friends", null,
   new AVIMConversationCreatedCallback() {
      @Override
      public void done(AVIMConversation conversation, AVIMException e) {
           if (e == null) {
              // Conversation created
           }
      }
   });

var conversation = await tom.CreateConversationAsync(new string[]{ "Jerry","Mary" }, name:"Tom & Jerry & friends", isUnique:true);

Sending Group Messages

In a group chat, if a member sends a message, the message will be delivered to all the online members in the group. The process is the same as how Jerry receives the message from Tom.

For example, if Tom sends a welcoming message to the group:

conversation.send(new TextMessage('Welcome everyone!'));

[conversation sendMessage:[AVIMTextMessage messageWithText:@"Welcome everyone!" attributes:nil] callback:^(BOOL succeeded, NSError *error) {
    if (succeeded) {
        NSLog(@"Message sent!");
    }
}];

AVIMTextMessage msg = new AVIMTextMessage();
msg.setText("Welcome everyone!");
// Send the message
conversation.sendMessage(msg, new AVIMConversationCallback() {
  @Override
  public void done(AVIMException e) {
    if (e == null) {
      Log.d("Group chat", "Message sent!");
    }
  }
});

var textMessage = new AVIMTextMessage("Welcome everyone!");
await conversation.SendMessageAsync(textMessage);

Both Jerry and Mary will have Event.MESSAGE event triggered which can be used to retrieve the message and have it displayed on the UI.

Removing Members

One day Mary spoke something that made Tom angry and Tom wants to kick her out of the group chat. How would Tom do that?

conversation.remove(['Mary']).then(function(conversation) {
  console.log('Member removed!', conversation.members);
}).catch(console.error.bind(console));

[conversation removeMembersWithClientIds:@[@"Mary"] callback:^(BOOL succeeded, NSError *error) {
    if (succeeded) {
        NSLog(@"Member removed!");
    }
}];

conv.kickMembers(Arrays.asList("Mary"),new AVIMConversationCallback(){
    @Override
    public void done(AVIMException e){
    }
});

await conversation.RemoveMembersAsync("Mary");

The following process will be triggered:

Tom->Cloud: 1. Removes Mary
Cloud-->Mary: 2. Send notification: You are removed by Tom
Cloud-->Jerry: 2. Send notification: Mary is removed by Tom
Cloud-->Tom: 2. Send notification: Mary is removed

Here we see that Mary receives KICKED which indicates that she (the current user) is removed. Other members (Jerry and Tom) will receive MEMBERS_LEFT which indicates that someone else in the conversation is removed. Such events can be handled with the following code:

// Someone else is removed
jerry.on(Event.MEMBERS_LEFT, function membersjoinedEventHandler(payload, conversation) {
    console.log(payload.members, payload.kickedBy, conversation.id);
});
// The current user is removed
jerry.on(Event.KICKED, function membersjoinedEventHandler(payload, conversation) {
    console.log(payload.kickedBy, conversation.id);
});

jerry.delegate = self;

#pragma mark - AVIMClientDelegate
/*!
 Someone else is removed
 @param conversation － The conversation
 @param clientIds - The list of members being removed
 @param clientId - The ID of the operator
 */
- (void)conversation:(AVIMConversation *)conversation membersRemoved:(NSArray<NSString *> * _Nullable)clientIds byClientId:(NSString * _Nullable)clientId {
  ;
}
/*!
 The current user is removed
 @param conversation － The conversation
 @param clientId - The ID of the operator
 */
- (void)conversation:(AVIMConversation *)conversation kickedByClientId:(NSString * _Nullable)clientId {
  ;
}

public class CustomConversationEventHandler extends AVIMConversationEventHandler {
  /**
   * Someone else is removed
   *
   * @param client
   * @param conversation
   * @param members The members being removed
   * @param kickedBy The ID of the operator; could be the current user itself
   * @since 3.0
   */
  @Override
  public abstract void onMemberLeft(AVIMClient client,
    AVIMConversation conversation, List<String> members, String kickedBy) {
    Toast.makeText(AVOSCloud.applicationContext,
      members + "  are removed from " + conversation.getConversationId() + " by "
          + kickedBy, Toast.LENGTH_SHORT).show();
  }
  /**
   * The current user is removed
   *
   * @param client
   * @param conversation
   * @param kickedBy The person who removed you
   * @since 3.0
   */
  @Override
  public abstract void onKicked(AVIMClient client, AVIMConversation conversation,
    String kickedBy) {
    Toast.makeText(AVOSCloud.applicationContext,
      "You are removed from " + conversation.getConversationId() + " by "
          + kickedBy, Toast.LENGTH_SHORT).show();
  }
}
// Set up global event handler
AVIMMessageManager.setConversationEventHandler(new CustomConversationEventHandler());

private void OnMembersLeft(object sender, AVIMOnInvitedEventArgs e)
{
    Debug.Log(string.Format("{0} removed {1} from {2}", e.KickedBy, e.JoinedMembers, e.ConversationId));
}
private void OnKicked(object sender, AVIMOnInvitedEventArgs e)
{
    Debug.Log(string.Format("You are removed from {2} by {1}", e.KickedBy, e.ConversationId));
}
jerry.OnMembersLeft += OnMembersLeft;
jerry.OnKicked += OnKicked;

Joining Conversations

Tom is feeling bored after removing Mary. He goes to William and tells him that there is a group chat that Jerry and himself are in. He gives the ID (or name) of the group chat to William which makes him curious about what's going on in it. William then adds himself to the group:

william.getConversation('CONVERSATION_ID').then(function(conversation) {
  return conversation.join();
}).then(function(conversation) {
  console.log('Successfully joined!', conversation.members);
  // The conversation now contains ['William', 'Tom', 'Jerry']
}).catch(console.error.bind(console));

AVIMConversationQuery *query = [william conversationQuery];
[query getConversationById:@"CONVERSATION_ID" callback:^(AVIMConversation *conversation, NSError *error) {
    [conversation joinWithCallback:^(BOOL succeeded, NSError *error) {
        if (succeeded) {
            NSLog(@"Successfully joined!");
        }
    }];
}];

AVIMConversation conv = william.getConversation("CONVERSATION_ID");
conv.join(new AVIMConversationCallback(){
    @Override
    public void done(AVIMException e){
        if(e==null){
          // Successfully joined
        }
    }
});

await william.JoinAsync("CONVERSATION_ID");

The following process will be triggered:

William->Cloud: 1. Joins the conversations
Cloud-->William: 2. Sends notification: you joined the conversation
Cloud-->Tom: 2. Sends notification: William joined the conversation
Cloud-->Jerry: 2. Sends notification: William joined the conversation

Other members can listen to MEMBERS_JOINED to know that William joined the conversation:

jerry.on(Event.MEMBERS_JOINED, function membersJoinedEventHandler(payload, conversation) {
    console.log(payload.members, payload.invitedBy, conversation.id);
});

- (void)conversation:(AVIMConversation *)conversation membersAdded:(NSArray *)clientIds byClientId:(NSString *)clientId {
    NSLog(@"%@", [NSString stringWithFormat:@"%@ joined the conversation; operated by %@",[clientIds objectAtIndex:0],clientId]);
}

public class CustomConversationEventHandler extends AVIMConversationEventHandler {
  @Override
  public void onMemberJoined(AVIMClient client, AVIMConversation conversation,
      List<String> members, String invitedBy) {
      // Shows that William joined 551260efe4b01608686c3e0f; operated by William
      Toast.makeText(AVOSCloud.applicationContext,
        members + " joined " + conversation.getConversationId() + "; operated by "
            + invitedBy, Toast.LENGTH_SHORT).show();
  }
}

private void OnMembersJoined(object sender, AVIMOnInvitedEventArgs e)
{
    // e.InvitedBy is the operator; e.ConversationId is the ID of the conversation
    Debug.Log(string.Format("{0} joined {1}; operated by {2}",e.JoinedMembers, e.ConversationId, e.InvitedBy));
}
jerry.OnMembersJoined += OnMembersJoined;

Leaving Conversations

With more and more people being invited by Tom, Jerry feels that he doesn't like most of them and wants to leave the conversation. He can do that with Conversation#quit:

conversation.quit().then(function(conversation) {
  console.log('You left the conversation!', conversation.members);
}).catch(console.error.bind(console));

[conversation quitWithCallback:^(BOOL succeeded, NSError *error) {
    if (succeeded) {
        NSLog(@"You left the conversation!");
    }
}];

conversation.quit(new AVIMConversationCallback(){
    @Override
    public void done(AVIMException e){
      if(e==null){
        // You left the conversation
      }
    }
});

await jerry.LeaveAsync(conversation);

After leaving the conversation, Jerry will no longer receive messages from it. Here is the sequence diagram of the operation:

Jerry->Cloud: 1. Leaves the conversation
Cloud-->Jerry: 2. Sends notification: You left the conversation
Cloud-->Mary: 2. Sends notification: Jerry left the conversation
Cloud-->Tom: 2. Sends notification: Jerry left the conversation

Other members can listen to MEMBERS_LEFT to know that Jerry left the conversation:

mary.on(Event.MEMBERS_LEFT, function membersLeftEventHandler(payload, conversation) {
    console.log(payload.members, payload.kickedBy, conversation.id);
});

// If Mary is logged in, the following callback will be triggered when Jerry leaves the conversation
-(void)conversation:(AVIMConversation *)conversation membersRemoved:(NSArray *)clientIds byClientId:(NSString *)clientId{
    NSLog(@"%@", [NSString stringWithFormat:@"%@ left the conversation; operated by %@",[clientIds objectAtIndex:0],clientId]);
}

public class CustomConversationEventHandler extends AVIMConversationEventHandler {
  @Override
  public void onMemberLeft(AVIMClient client, AVIMConversation conversation, List<String> members,
      String kickedBy) {
      // Things to do after someone left
  }
}

mary.OnMembersLeft += OnMembersLeft;
private void OnMembersLeft(object sender, AVIMOnMembersLeftEventArgs e)
{
    // e.KickedBy is the operator; e.ConversationId is the ID of the conversation
    Debug.Log(string.Format("{0} left {1}; operated by {2}",e.JoinedMembers, e.ConversationId, e.KickedBy));
}

Summary of Event Notifications Regarding Changes of Members

The sequence diagrams displayed earlier already described what would happen when certain events are triggered. The table below serves as a summary of them.

Assuming that Tom and Jerry are already in the conversation:

Operation	Tom	Jerry	Mary	William
Tom invites Mary	`MEMBERS_JOINED`	`MEMBERS_JOINED`	`INVITED`	/
Tom removes Mary	`MEMBERS_LEFT`	`MEMBERS_LEFT`	`KICKED`	/
William joins	`MEMBERS_JOINED`	`MEMBERS_JOINED`	/	`MEMBERS_JOINED`
Jerry leaves	`MEMBERS_LEFT`	`MEMBERS_LEFT`	/	`MEMBERS_LEFT`

Rich Media Messages

We've seen how we can send messages containing plain text. Now let's see how we can send rich media messages like images, videos, and locations.

By default LeanCloud supports text messages, files, images, audios, videos, locations, and binary data. All of them, except binary data, are sent as strings, though there are some slight differences between text messages and rich media messages (files, images, audios, and videos):

When sending text messages, the messages themselves are sent directly as strings.
When sending rich media messages (like images), the SDK will first upload the binary files to the cloud with LeanStorage's AVFile interface, then embed the URLs of them into the messages being sent. We can say that the essence of an image message is a text message holding the URL of the image.

Files stored on LeanStorage have CDN enabled by default. Therefore, binary data (like images) are not directly encoded as part of text messages. This helps users access them faster and the cost on you can be lowered at the same time.

Default Message Types

The following message types are offered by default:

TextMessage Text message
ImageMessage Image message
AudioMessage Audio message
VideoMessage Video message
FileMessage File message (.txt, .doc, .md, etc.)
LocationMessage Location message

All of them are derived from AVIMMessage, with the following properties available for each:

Name	Type	Description
`from`	`String`	The `clientId` of the sender.
`cid`	`String`	The ID of the conversation.
`id`	`String`	A unique ID for each message. Assigned by the cloud automatically.
`timestamp`	`Date`	The time the message is sent. Assigned by the cloud automatically.
`deliveredAt`	`Date`	The time the message is delivered. Assigned by the cloud automatically.
`status`	`Symbol`	The status of the message. Could be one of the members of `MessageStatus` `MessageStatus.SENDING` (sending) `MessageStatus.SENT` (sent) `MessageStatus.DELIVERED` (delivered) `MessageStatus.FAILED` (failed)

Name	Type	Description
`content`	`NSString`	The content of the message.
`clientId`	`NSString`	The `clientId` of the sender.
`conversationId`	`NSString`	The ID of the conversation.
`messageId`	`NSString`	A unique ID for each message. Assigned by the cloud automatically.
`sendTimestamp`	`int64_t`	The time the message is sent. Assigned by the cloud automatically.
`deliveredTimestamp`	`int64_t`	The time the message is delivered. Assigned by the cloud automatically.
`status`	A member of `AVIMMessageStatus`	The status of the message. Could be one of: `AVIMMessageStatusNone` (unknown) `AVIMMessageStatusSending` (sending) `AVIMMessageStatusSent` (sent) `AVIMMessageStatusDelivered` (delivered) `AVIMMessageStatusFailed` (failed)
`ioType`	A member of `AVIMMessageIOType`	The direction of the message. Could be one of: `AVIMMessageIOTypeIn` (sent to the current user) `AVIMMessageIOTypeOut` (sent by the current user)

Name	Type	Description
`content`	`String`	The content of the message.
`clientId`	`String`	The `clientId` of the sender.
`conversationId`	`String`	The ID of the conversation.
`messageId`	`String`	A unique ID for each message. Assigned by the cloud automatically.
`timestamp`	`long`	The time the message is sent. Assigned by the cloud automatically.
`receiptTimestamp`	`long`	The time the message is delivered. Assigned by the cloud automatically.
`status`	A member of `AVIMMessageStatus`	The status of the message. Could be one of: `AVIMMessageStatusNone` (unknown) `AVIMMessageStatusSending` (sending) `AVIMMessageStatusSent` (sent) `AVIMMessageStatusReceipt` (delivered) `AVIMMessageStatusFailed` (failed)
`ioType`	A member of `AVIMMessageIOType`	The direction of the message. Could be one of: `AVIMMessageIOTypeIn` (sent to the current user) `AVIMMessageIOTypeOut` (sent by the current user)

Name	Type	Description
`content`	`String`	The content of the message.
`clientId`	`String`	The `clientId` of the sender.
`conversationId`	`String`	The ID of the conversation.
`messageId`	`String`	A unique ID for each message. Assigned by the cloud automatically.
`timestamp`	`long`	The time the message is sent. Assigned by the cloud automatically.
`receiptTimestamp`	`long`	The time the message is delivered. Assigned by the cloud automatically.
`status`	A member of `AVIMMessageStatus`	The status of the message. Could be one of: `AVIMMessageStatusNone` (unknown) `AVIMMessageStatusSending` (sending) `AVIMMessageStatusSent` (sent) `AVIMMessageStatusReceipt` (delivered) `AVIMMessageStatusFailed` (failed)
`ioType`	A member of `AVIMMessageIOType`	The direction of the message. Could be one of: `AVIMMessageIOTypeIn` (sent to the current user) `AVIMMessageIOTypeOut` (sent by the current user)

A number is assigned to each message type which can be used by your app to identify it. Negative numbers are for those defined by the SDK (see the table below) and positive ones are for your own types. 0 is reserved for untyped messages.

Message Type	Number
Text messages	`-1`
Image messages	`-2`
Audio messages	`-3`
Video messages	`-4`
Location messages	`-5`
File messages	`-6`

Image Messages

Sending Image Files

A image message can be constructed from either binary data or a local path. The diagram below shows the sequence of it:

Tom-->Local: 1. Get the content of the image
Tom-->Storage: 2. The SDK uploads the file (AVFile) to the cloud
Storage-->Tom: 3. Return the URL of the image
Tom-->Cloud: 4. The SDK sends the image message to the cloud
Cloud->Jerry: 5. Receive the image message and display that in UI

Notes:

The "Local" in the diagram could be localStorage or camera, meaning that the image could be either from the local storage of the phone (like iPhone's Camera Roll) or taken in real time with camera API.
AVFile is the file object used by LeanStorage. See AVFile for more details.

The diagram above may look complicated, but the code itself is quite simple since the image gets automatically uploaded when being sent with send method:

var AV = require('leancloud-storage');
var { ImageMessage } = require('leancloud-realtime-plugin-typed-messages');

var fileUploadControl = $('#photoFileUpload')[0];
var file = new AV.File('avatar.jpg', fileUploadControl.files[0]);
file.save().then(function() {
  var message = new ImageMessage(file);
  message.setText('Sent via Ins.');
  message.setAttributes({ location: 'San Francisco' });
  return conversation.send(message);
}).then(function() {
  console.log('Sent!');
}).catch(console.error.bind(console));

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *imagePath = [documentsDirectory stringByAppendingPathComponent:@"LeanCloud.png"];
NSError *error;
AVFile *file = [AVFile fileWithLocalPath:imagePath error:&error];
AVIMImageMessage *message = [AVIMImageMessage messageWithText:@"She is sweet." file:file attributes:nil];
[conversation sendMessage:message callback:^(BOOL succeeded, NSError *error) {
    if (succeeded) {
        NSLog(@"Sent!");
    }
}];

AVFile file = AVFile.withAbsoluteLocalPath("San_Francisco.png", Environment.getExternalStorageDirectory() + "/San_Francisco.png");
// Create an image message
AVIMImageMessage m = new AVIMImageMessage(file);
m.setText("Sent via Android.");
conv.sendMessage(m, new AVIMConversationCallback() {
  @Override
  public void done(AVIMException e) {
    if (e == null) {
      // Sent
    }
  }
});

var image = new AVFile("screenshot.png", Path.Combine(Application.persistentDataPath, "screenshot.PNG"));
var imageMessage = new AVIMImageMessage();
imageMessage.File = image;
imageMessage.TextContent = "Sent via Windows.";
await conversation.SendMessageAsync(imageMessage);

Sending Image URLs

Beside sending an image directly, a user may also copy the URL of an image from somewhere else and send it to a conversation:

var AV = require('leancloud-storage');
var { ImageMessage } = require('leancloud-realtime-plugin-typed-messages');
// Create an image message from URL
var file = new AV.File.withURL('cute-girl', 'http://pic2.zhimg.com/6c10e6053c739ed0ce676a0aff15cf1c.gif');
file.save().then(function() {
  var message = new ImageMessage(file);
  message.setText('She is sweet.');
  return conversation.send(message);
}).then(function() {
  console.log('Sent!');
}).catch(console.error.bind(console));

// Tom sends an image to Jerry
AVFile *file = [AVFile fileWithURL:[self @"http://ww3.sinaimg.cn/bmiddle/596b0666gw1ed70eavm5tg20bq06m7wi.gif"]];
AVIMImageMessage *message = [AVIMImageMessage messageWithText:@"She is sweet." file:file attributes:nil];
[conversation sendMessage:message callback:^(BOOL succeeded, NSError *error) {
    if (succeeded) {
        NSLog(@"Sent!");
    }
}];

AVFile file = new AVFile("cute-girl","http://ww3.sinaimg.cn/bmiddle/596b0666gw1ed70eavm5tg20bq06m7wi.gif", null);
AVIMImageMessage m = new AVIMImageMessage(file);
m.setText("She is sweet.");
// Create an image message
conv.sendMessage(m, new AVIMConversationCallback() {
    @Override
    public void done(AVIMException e) {
      if (e == null) {
        // Sent
      }
    }
});

var image = new AVFile("Satomi_Ishihara.gif", "http://ww3.sinaimg.cn/bmiddle/596b0666gw1ed70eavm5tg20bq06m7wi.gif");
var imageMessage = new AVIMImageMessage();
imageMessage.File = image;
imageMessage.TextContent = "Sent via Windows.";
await conversation.SendMessageAsync(imageMessage);

Receiving Image Messages

The way to receive image messages is similar to that for basic messages. The only thing that needs to be added is to have the callback function retrieve the image and render it on the UI. For example:

var { Event, TextMessage } = require('leancloud-realtime');
var { ImageMessage } = require('leancloud-realtime-plugin-typed-messages');

client.on(Event.MESSAGE, function messageEventHandler(message, conversation) {
   var file;
   switch (message.type) {
      case ImageMessage.TYPE:
        file = message.getFile();
        console.log('Image received. URL: ' + file.url());
        break;
   }
}

- (void)conversation:(AVIMConversation *)conversation didReceiveTypedMessage:(AVIMTypedMessage *)message {
    AVIMImageMessage *imageMessage = (AVIMImageMessage *)message;

    // The ID of the message
    NSString *messageId = imageMessage.messageId;
    // The URL of the image file
    NSString *imageUrl = imageMessage.file.url;
    // The clientId of the sender
    NSString *fromClientId = message.clientId;
}

AVIMMessageManager.registerMessageHandler(AVIMImageMessage.class,
    new AVIMTypedMessageHandler<AVIMImageMessage>() {
        @Override
        public void onMessage(AVIMImageMessage msg, AVIMConversation conv, AVIMClient client) {
            // Only handle messages from Jerry
            // sent to the conversation with conversationId 55117292e4b065f7ee9edd29
            if ("Jerry".equals(client.getClientId()) && "55117292e4b065f7ee9edd29".equals(conv.getConversationId())) {
                String fromClientId = msg.getFrom();
                String messageId = msg.getMessageId();
                String url = msg.getFileUrl();
                Map<String, Object> metaData = msg.getFileMetaData();
                if (metaData.containsKey("size")) {
                  int size = (Integer) metaData.get("size");
                }
                if (metaData.containsKey("width")) {
                  int width = (Integer) metaData.get("width");
                }
                if (metaData.containsKey("height")) {
                  int height = (Integer) metaData.get("height");
                }
                if (metaData.containsKey("format")) {
                  String format = (String) metaData.get("format");
                }
            }
        }
});

private void OnMessageReceived(object sender, AVIMMessageEventArgs e)
{
    if (e.Message is AVIMImageMessage imageMessage)
    {
        AVFile file = imageMessage.File;
        Debug.Log(file.Url);
    }
}

Sending Audios, Videos, and Files

The Flow

The SDK follows the steps below to send images, audios, videos, and files:

When constructing files from data streams using client API:

Construct a local AVFile
Upload the AVFile to the cloud and retrieve its metaData
Embed the objectId, URL, and metadata of the file into the message
Send the message

When constructing files with URLs:

Embed the URL into the message without metadata (like the length of audio) or objectId
Send the message

For example, when sending an audio message, the basic flow would be: read the audio file (or record a new one) > construct an audio message > send the message.

var AV = require('leancloud-storage');
var { AudioMessage } = require('leancloud-realtime-plugin-typed-messages');

var fileUploadControl = $('#musicFileUpload')[0];
var file = new AV.File('never-gonna-give-you-up.mp3', fileUploadControl.files[0]);
file.save().then(function() {
  var message = new AudioMessage(file);
  message.setText('I heard this song became a meme.');
  return conversation.send(message);
}).then(function() {
  console.log('Sent!');
}).catch(console.error.bind(console));

NSError *error = nil;
AVFile *file = [AVFile fileWithLocalPath:localPath error:&error];
if (!error) {
    AVIMAudioMessage *message = [AVIMAudioMessage messageWithText:@"I heard this song became a meme." file:file attributes:nil];
    [conversation sendMessage:message callback:^(BOOL succeeded, NSError *error) {
        if (succeeded) {
            NSLog(@"Sent!");
        }
    }];
}

AVFile file = AVFile.withAbsoluteLocalPath("never-gonna-give-you-up.mp3",localFilePath);
AVIMAudioMessage m = new AVIMAudioMessage(file);
m.setText("I heard this song became a meme.");
// Create an audio message
conv.sendMessage(m, new AVIMConversationCallback() {
    @Override
    public void done(AVIMException e) {
      if (e == null) {
        // Sent
      }
    }
});

var audio = new AVFile("never-gonna-give-you-up.mp3", Path.Combine(Application.persistentDataPath, "never-gonna-give-you-up.mp3"));
var audioMessage = new AVIMAudioMessage();
audioMessage.File = audio;
audioMessage.TextContent = "I heard this song became a meme.";
await conversation.SendMessageAsync(audioMessage);

Similar to image messages, you can construct audio messages from URLs as well:

var AV = require('leancloud-storage');
var { AudioMessage } = require('leancloud-realtime-plugin-typed-messages');

var file = new AV.File.withURL('apple.acc', 'https://some.website.com/apple.acc');
file.save().then(function() {
  var message = new AudioMessage(file);
  message.setText('Here is the recording from Apple Special Event.');
  return conversation.send(message);
}).then(function() {
  console.log('Sent!');
}).catch(console.error.bind(console));

AVFile *file = [AVFile fileWithRemoteURL:[NSURL URLWithString:@"https://some.website.com/apple.acc"]];
AVIMAudioMessage *message = [AVIMAudioMessage messageWithText:@"Here is the recording from Apple Special Event." file:file attributes:nil];
[conversation sendMessage:message callback:^(BOOL succeeded, NSError *error) {
    if (succeeded) {
        NSLog(@"Sent!");
    }
}];

AVFile file = new AVFile("apple.acc", "https://some.website.com/apple.acc", null);
AVIMAudioMessage m = new AVIMAudioMessage(file);
m.setText("Here is the recording from Apple Special Event.");
conv.sendMessage(m, new AVIMConversationCallback() {
    @Override
    public void done(AVIMException e) {
      if (e == null) {
        // Sent
      }
    }
});

var audio = new AVFile("apple.acc", "https://some.website.com/apple.acc");
var audioMessage = new AVIMAudioMessage();
audioMessage.File = audio;
audioMessage.TextContent = "Here is the recording from Apple Special Event.";
await conversation.SendMessageAsync(audioMessage);

Sending Location Messages

The code below sends a message containing a location:

var AV = require('leancloud-storage');
var { LocationMessage } = require('leancloud-realtime-plugin-typed-messages');

var location = new AV.GeoPoint(31.3753285,120.9664658);
var message = new LocationMessage(location);
message.setText('Here is the location of the bakery.');
conversation.send(message).then(function() {
  console.log('Sent!');
}).catch(console.error.bind(console));

AVIMLocationMessage *message = [AVIMLocationMessage messageWithText:@"Here is the location of the bakery." latitude:31.3753285 longitude:120.9664658 attributes:nil];
[conversation sendMessage:message callback:^(BOOL succeeded, NSError *error) {
    if (succeeded) {
        NSLog(@"Sent!");
    }
}];

final AVIMLocationMessage locationMessage = new AVIMLocationMessage();
// The location here is hardcoded for demonstration; you can get actual locations with the API offered by the device
locationMessage.setLocation(new AVGeoPoint(31.3753285,120.9664658));
locationMessage.setText("Here is the location of the bakery.");
conversation.sendMessage(locationMessage, new AVIMConversationCallback() {
    @Override
    public void done(AVIMException e) {
        if (null != e) {
          e.printStackTrace();
        } else {
          // Sent
        }
    }
});

var locationMessage = new AVIMLocationMessage();
locationMessage.Location = new AVGeoPoint(31.3753285, 120.9664658);
await conversation.SendMessageAsync(locationMessage);

Back to Receiving Messages

When a new message comes in, no matter what type of message it is, the JavaScript SDK would always trigger the callback set for the event Event.MESSAGE on IMClient. You can address different types of messages in different ways within the callback function.

The Objective-C SDK handles new messages with AVIMClientDelegate and uses two separate methods to handle basic messages (AVIMMessage) and rich media messages (AVIMTypedMessage; including messages with custom types):

/*!
 New basic message received.
 @param conversation － The conversation.
 @param message - The content of the message.
 */
- (void)conversation:(AVIMConversation *)conversation didReceiveCommonMessage:(AVIMMessage *)message;

/*!
 New rich media message received.
 @param conversation － The conversation.
 @param message - The content of the message.
 */
- (void)conversation:(AVIMConversation *)conversation didReceiveTypedMessage:(AVIMTypedMessage *)message;

The Java/Android SDK handles new messages with AVIMMessageHandler. You can register your own message handlers by calling AVIMMessageManager#registerDefaultMessageHandler. AVIMMessageManager offers two different methods for you to register default message handlers and handlers for specific message types:

/**
 * Register default message handler.
 *
 * @param handler
 */
public static void registerDefaultMessageHandler(AVIMMessageHandler handler);
/**
 * Register handler for specific message type.
 *
 * @param clazz The message type
 * @param handler
 */
public static void registerMessageHandler(Class<? extends AVIMMessage> clazz, MessageHandler<?> handler);
/**
 * Deregister handler for specific message type.
 *
 * @param clazz
 * @param handler
 */
public static void unregisterMessageHandler(Class<? extends AVIMMessage> clazz, MessageHandler<?> handler);

Different handlers can be registered or deregistered for different message types (including those defined by yourself). These handlers should be set up when initializing the app.

If you call registerDefaultMessageHandler on AVIMMessageManager for multiple times, only the last one would work. However, if you register AVIMMessageHandler through registerMessageHandler, different handlers could coexist with each other.

When a message is received by the client, the SDK would:

Detect the type of the message, look for all the handlers registered for this type, and call the onMessage functions within all these handlers.
If no handler is found for this type, defaultHandler will be triggered.

So when handlers are specified for AVIMTypedMessage (and its subtypes) and a global defaultHandler is also specified, if the sender sends a general AVIMMessage message, the receiver will have its handler in AVIMMessageManager#registerDefaultMessageHandler() triggered; if the sender sends a message of AVIMTypedMessage (or its subtype), the receiver will have its handler in AVIMMessageManager#registerMessageHandler() triggered.

The C# SDK handles new messages with OnMessageReceived. There are two levels here:

The first level is applied to AVIMClient which serves to get you notified that there are messages coming in. This is especially helpful when there is no local AVIMConversation (like when a user just logged in) and a new message is sent to a conversation involving the current user. AVIMClient.OnMessageReceived would take in the messages, but has nothing to do with the type of the message.
The second level is applied to AVIMConversation which serves to receive the actual messages and perform different operations for different types of messages.

The table below illustrates how these two levels work. Assuming that we are receiving an AVIMTextMessage:

Receiver's `AVIMClient`	Condition 1	Condition 2	Condition 3	Condition 4	Condition 5
`AVIMClient.OnMessageReceived`	×	√	√	√	√
`AVIMConversation.OnMessageReceived`	×	×	√	×	×
`AVIMConversation.OnTypedMessageReceived`	×	×	×	√	×
`AVIMConversation.OnTextMessageReceived`	×	×	×	×	√

Below are the conditions:

Condition 1:

AVIMClient.Status != Online

Condition 2:

   AVIMClient.Status == Online 
&& AVIMClient.OnMessageReceived != null

Condition 3:

   AVIMClient.Status == Online 
&& AVIMClient.OnMessageReceived != null 
&& AVIMConversation.OnMessageReceived != null

Condition 4:

   AVIMClient.Status == Online 
&& AVIMClient.OnMessageReceived != null 
&& AVIMConversation.OnMessageReceived != null
&& AVIMConversation.OnTypedMessageReceived != null
&& AVIMConversation.OnTextMessageReceived == null

Condition 5:

   AVIMClient.Status == Online 
&& AVIMClient.OnMessageReceived != null 
&& AVIMConversation.OnMessageReceived != null
&& AVIMConversation.OnTypedMessageReceived != null
&& AVIMConversation.OnTextMessageReceived != null

In AVIMConversation, the process of receiving a message is:

OnTextMessageReceived > OnTypedMessageReceived > OnMessageReceived

Such design allows you to assign different operations to different layers. It works for other types of rich media messages as well.

Below is an example:

// Load TypedMessagesPlugin when initializing Realtime
// var realtime = new Realtime({
//   appId: appId,
//   plugins: [TypedMessagesPlugin]
// });
var { Event, TextMessage } = require('leancloud-realtime');
var { FileMessage, ImageMessage, AudioMessage, VideoMessage, LocationMessage } = require('leancloud-realtime-plugin-typed-messages');
// Register handler for MESSAGE event
client.on(Event.MESSAGE, function messageEventHandler(message, conversation) {
  // Your logic here
  var file;
  switch (message.type) {
    case TextMessage.TYPE:
      console.log('Text message received. Text: ' + message.getText() + ', ID: ' + message.id);
      break;
    case FileMessage.TYPE:
      file = message.getFile(); // file is an AV.File instance
      console.log('File message received. URL: ' + file.url() + ', Size: ' + file.metaData('size'));
      break;
    case ImageMessage.TYPE:
      file = message.getFile();
      console.log('Image message received. URL: ' + file.url() + ', Width: ' + file.metaData('width'));
      break;
    case AudioMessage.TYPE:
      file = message.getFile();
      console.log('Audio message received. URL: ' + file.url() + ', Duration: ' + file.metaData('duration'));
      break;
    case VideoMessage.TYPE:
      file = message.getFile();
      console.log('Video message received. URL: ' + file.url() + ', Duration: ' + file.metaData('duration'));
      break;
    case LocationMessage.TYPE:
      var location = message.getLocation();
      console.log('Location message received. Latitude: ' + location.latitude + ', Longitude: ' + location.longitude);
      break;
    default:
      console.warn('Message with unknown type received.');
  }
});

// `MESSAGE` event will be triggered on conversation as well
conversation.on(Event.MESSAGE, function messageEventHandler(message) {
  // Your logic here
});

// Handle messages with built-in types
- (void)conversation:(AVIMConversation *)conversation didReceiveTypedMessage:(AVIMTypedMessage *)message {
    if (message.mediaType == kAVIMMessageMediaTypeImage) {
        AVIMImageMessage *imageMessage = (AVIMImageMessage *)message; // Handle image message
    } else if(message.mediaType == kAVIMMessageMediaTypeAudio){
        // Handle audio message
    } else if(message.mediaType == kAVIMMessageMediaTypeVideo){
        // Handle video message
    } else if(message.mediaType == kAVIMMessageMediaTypeLocation){
        // Handle location message
    } else if(message.mediaType == kAVIMMessageMediaTypeFile){
        // Handle file message
    } else if(message.mediaType == kAVIMMessageMediaTypeText){
        // Handle text message
    }
}

// Handle messages with custom types

// 1. Register subclass
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    [AVIMCustomMessage registerSubclass];
}
// 2. Receive message
- (void)conversation:(AVIMConversation *)conversation didReceiveTypedMessage:(AVIMTypedMessage *)message {
    if (message.mediaType == 1) {
        AVIMCustomMessage *imageMessage = (AVIMCustomMessage *)message;
        // Handle image message
    }
}

// 1. Register default handler
AVIMMessageManager.registerDefaultMessageHandler(new AVIMMessageHandler(){
    public void onMessage(AVIMMessage message, AVIMConversation conversation, AVIMClient client) {
        // Receive the message
    }

    public void onMessageReceipt(AVIMMessage message, AVIMConversation conversation, AVIMClient client) {
        // Do something after receiving the message
    }
});
// 2. Register handler for each type of message
AVIMMessageManager.registerMessageHandler(AVIMTypedMessage.class, new AVIMTypedMessageHandler<AVIMTypedMessage>(){
    public void onMessage(AVIMTypedMessage message, AVIMConversation conversation, AVIMClient client) {
        switch (message.getMessageType()) {
            case AVIMMessageType.TEXT_MESSAGE_TYPE:
                // Do something
                AVIMTextMessage textMessage = (AVIMTextMessage)message;
                break;
            case AVIMMessageType.IMAGE_MESSAGE_TYPE:
                // Do something
                AVIMImageMessage imageMessage = (AVIMImageMessage)message;
                break;
            case AVIMMessageType.AUDIO_MESSAGE_TYPE:
                // Do something
                AVIMAudioMessage audioMessage = (AVIMAudioMessage)message;
                break;
            case AVIMMessageType.VIDEO_MESSAGE_TYPE:
                // Do something
                AVIMVideoMessage videoMessage = (AVIMVideoMessage)message;
                break;
            case AVIMMessageType.LOCATION_MESSAGE_TYPE:
                // Do something
                AVIMLocationMessage locationMessage = (AVIMLocationMessage)message;
                break;
            case AVIMMessageType.FILE_MESSAGE_TYPE:
                // Do something
                AVIMFileMessage fileMessage = (AVIMFileMessage)message;
                break;
            case AVIMMessageType.RECALLED_MESSAGE_TYPE:
                // Do something
                AVIMRecalledMessage recalledMessage = (AVIMRecalledMessage)message;
                break;
            default:
                // UnsupportedMessageType
                break;
        }
    }

    public void onMessageReceipt(AVIMTypedMessage message, AVIMConversation conversation, AVIMClient client) {
        // Do something after receiving the message
    }
});

// Handle messages with custom types
public class CustomMessage extends AVIMMessage {

}

AVIMMessageManager.registerMessageHandler(CustomMessage.class, new MessageHandler<CustomMessage>(){
    public void onMessage(CustomMessage message, AVIMConversation conversation, AVIMClient client) {
        // Receive the message
    }

    public void onMessageReceipt(CustomMessage message, AVIMConversation conversation, AVIMClient client){
        // Do something after receiving the message
    }
});

// Here is a simple demo; you may use switch/case instead
private void OnMessageReceived(object sender, AVIMMessageEventArgs e)
{
    if (e.Message is AVIMImageMessage imageMessage)
    {

    }
    else if (e.Message is AVIMAudioMessage audioMessage)
    {

    }
    else if (e.Message is AVIMVideoMessage videoMessage)
    {

    }
    else if (e.Message is AVIMFileMessage fileMessage)
    {

    }
    else if (e.Message is AVIMLocationMessage locationMessage)
    {

    }
    else if (e.Message is AVIMTypedMessage baseTypedMessage)
    {

    } // Attach more conditions for custom types
}

Custom Attributes

A Conversation object holds some built-in properties which match the fields in the _Conversation table. The table below shows these built-in properties:

Property of `Conversation`	Field in `_Conversation`	Description
`id`	`objectId`	A globally unique ID.
`name`	`name`	The name of the conversation. Shared by all members.
`members`	`m`	The list of members.
`creator`	`c`	The creator of the conversation.
`transient`	`tr`	Whether it is a chat room.
`system`	`sys`	Whether it is a system conversation.
`mutedMembers`	`mu`	The list of members that muted the conversation.
`muted`	N/A	Whether the current user muted the conversation.
`createdAt`	`createdAt`	The time the conversation is created.
`updatedAt`	`updatedAt`	The time the conversation is updated.
`lastMessageAt`	`lm`	The time the last message is sent.
`lastMessage`	N/A	The last message. Could be empty.
`unreadMessagesCount`	N/A	The number of unread messages.
`lastDeliveredAt`	N/A	The time the last message being delivered is sent (for one-on-one chatting only).
`lastReadAt`	N/A	The time the last message being read is sent (for one-on-one chatting only).

Property of `AVIMConversation`	Field in `_Conversation`	Description
`conversationId`	`objectId`	A globally unique ID.
`name`	`name`	The name of the conversation. Shared by all members.
`members`	`m`	The list of members.
`creator`	`c`	The creator of the conversation.
`attributes`	`attr`	Custom attributes.
`transient`	`tr`	Whether it is a chat room.
`createdAt`	`createdAt`	The time the conversation is created.
`updatedAt`	`updatedAt`	The time the conversation is updated.
`system`	`sys`	Whether it is a system conversation.
`lastMessageAt`	`lm`	The time the last message is sent.
`lastMessage`	N/A	The last message. Could be empty.
`muted`	N/A	Whether the current user muted the conversation.
`unreadMessagesCount`	N/A	The number of unread messages.
`lastDeliveredAt`	N/A	The time the last message being delivered is sent (for one-on-one chatting only).
`lastReadAt`	N/A	The time the last message being read is sent (for one-on-one chatting only).

Property of `AVIMConversation`	Field in `_Conversation`	Description
`conversationId`	`objectId`	A globally unique ID.
`name`	`name`	The name of the conversation. Shared by all members.
`members`	`m`	The list of members.
`creator`	`c`	The creator of the conversation.
`attributes`	`attr`	Custom attributes.
`isTransient`	`tr`	Whether it is a chat room.
`lastMessageAt`	`lm`	The time the last message is sent.
`lastMessage`	N/A	The last message. Could be empty.
`muted`	N/A	Whether the current user muted the conversation.
`unreadMessagesCount`	N/A	The number of unread messages.
`lastDeliveredAt`	N/A	The time the last message being delivered is sent (for one-on-one chatting only).
`lastReadAt`	N/A	The time the last message being read is sent (for one-on-one chatting only).
`createdAt`	`createdAt`	The time the conversation is created.
`updatedAt`	`updatedAt`	The time the conversation is updated.
`system`	`sys`	Whether it is a system conversation.

Property of `AVIMConversation`	Field in `_Conversation`	Description
`Id`	`objectId`	A globally unique ID.
`Name`	`name`	The name of the conversation. Shared by all members.
`MemberIds`	`m`	The list of members.
`MuteMemberIds`	`mu`	The list of members that muted the conversation.
`Creator`	`c`	The creator of the conversation.
`IsTransient`	`tr`	Whether it is a chat room.
`IsUnique`	`unique`	If this is `true`, the same conversation will be reused when a new conversation is created with the same composition of members and `unique` to be `true`.
`IsSystem`	`sys`	Whether it is a system conversation.
`LastMessageAt`	`lm`	The time the last message is sent.
`LastMessage`	N/A	The last message. Could be empty.
`LastDeliveredAt`	N/A	The time the last message being delivered is sent (for one-on-one chatting only).
`LastReadAt`	N/A	The time the last message being read is sent (for one-on-one chatting only).
`CreatedAt`	`createdAt`	The time the conversation is created.
`UpdatedAt`	`updatedAt`	The time the conversation is updated.

Beside these built-in properties, you can also define your custom attributes to store more data with each conversation.

Creating Custom Attributes

When introducing one-on-one conversations, we mentioned that IMClient#createConversation allows you to attach custom attributes to a conversation. Now let's see how we can do that.

Assume that we need to add two properties { "type": "private", "pinned": true } to a conversation we are creating. We can do so by passing in the properties when calling IMClient#createConversation:

tom.createConversation({
  members: ['Jerry'],
  name: 'Tom & Jerry',
  unique: true,
  type: 'private',
  pinned: true,
}).then(function(conversation) {
  console.log('Conversation created! ID: ' + conversation.id);
}).catch(console.error.bind(console));

// Tom creates a conversation named "Tom & Jerry" and attaches custom attributes to it
NSDictionary *attributes = @{ 
    @"type": @"private",
    @"pinned": @(YES) 
};
[tom createConversationWithName:@"Tom & Jerry" clientIds:@[@"Jerry"] attributes:attributes options:AVIMConversationOptionUnique callback:^(AVIMConversation *conversation, NSError *error) {
    if (succeeded) {
        NSLog(@"Conversation created!");
    }
}];

HashMap<String,Object> attr = new HashMap<String,Object>();
attr.put("type","private");
attr.put("pinned",true);
client.createConversation(Arrays.asList("Jerry"),"Tom & Jerry", attr, false, true,
    new AVIMConversationCreatedCallback(){
        @Override
        public void done(AVIMConversation conv,AVIMException e){
          if(e==null){
            // Conversation created
          }
        }
    });

vars options = new Dictionary<string, object>();
options.Add("type", "private");
options.Add("pinned",true);
var conversation = await tom.CreateConversationAsync("Jerry", name:"Tom & Jerry", isUnique:true, options:options);

The SDK allows everyone in a conversation to access its custom attributes. You can even query conversations that satisfy certain attributes. See Querying Conversations with Custom Conditions.

Updating and Retrieving Properties

The built-in properties (like name) of a Conversation object can be updated by all the members unless you set restrictions in your app:

conversation.name = 'Tom is Smart';
conversation.save();

conversation[@"name"] = @"Tom is Smart";
[conversation updateWithCallback:^(BOOL succeeded, NSError * _Nullable error) {
    if (succeeded) {
        NSLog(@"Updated!");
    }
}];

AVIMConversation conversation = client.getConversation("55117292e4b065f7ee9edd29");
conversation.setName("Tom is Smart");
conversation.updateInfoInBackground(new AVIMConversationCallback(){
  @Override
  public void done(AVIMException e){        
    if(e==null){
      // Updated
    }
  }
});

conversation.Name = "Tom is Smart";
await conversation.SaveAsync();

Custom attributes can also be retrieved or updated by all the members:

// Retrieve custom attribute
var type = conversation.get('attr.type');
// Set new value for pinned
conversation.set('attr.pinned',false);
// Save
conversation.save();

// Retrieve custom attribute
NSString *type = [conversation objectForKey:@"attr.type"];
// Set new value for pinned
[conversation setObject:@(NO) forKey:@"attr.pinned"];
// Save
[conversation updateWithCallback:^(BOOL succeeded, NSError *error) {
    if (succeeded) {
        NSLog(@"Saved!");
    }
}];

// Retrieve custom attribute
String type = conversation.get("attr.type");
// Set new value for pinned
conversation.set("attr.pinned",false);
// Save
conversation.updateInfoInBackground(new AVIMConversationCallback(){
  @Override
  public void done(AVIMException e){        
    if(e==null){
      // Saved
    }
  }
});

// Retrieve custom attribute
var type = conversation["attr.type"];
// Set new value for pinned
conversation["attr.pinned"] = false;
// Save
await conversation.SaveAsync();

Notes about custom attributes:

The custom attributes specified with IMClient#createConversation will be stored in the field attr of the _Conversation table. If you need to retrieve or update them later, the full path needs to be specified, like attr.type.

Synchronization of Properties

The properties of a conversation (like name) are shared by everyone in it. If someone ever changes a property, other members need to get updated on it. In the example we used earlier, a user changed the name of a conversation to "Tom is Smart". How would other members get to know about it?

LeanMessage offers the mechanism that automatically delivers the change made by a user to a conversation to all the members in it (for those who are offline, they will receive updates once they get online):

/**
 * The properties of a conversation are updated
 * @event IMClient#CONVERSATION_INFO_UPDATED
 * @param {Object} payload
 * @param {Object} payload.attributes The properties being updated
 * @param {String} payload.updatedBy The ID of the operator
 */
var { Event } = require('leancloud-realtime');
client.on(Event.CONVERSATION_INFO_UPDATED, function(payload) {
});

/**
 The properties of a conversation are updated

 @param conversation The conversation
 @param date The time of the update
 @param clientId The ID of the operator
 @param data The data being updated
 */
- (void)conversation:(AVIMConversation *)conversation didUpdateAt:(NSDate * _Nullable)date byClientId:(NSString * _Nullable)clientId updatedData:(NSDictionary * _Nullable)data;

// The following definition exists in AVIMConversationEventHandler
/**
 * The properties of a conversation are updated
 *
 * @param client
 * @param conversation
 * @param attr      The properties being updated
 * @param operator  The ID of the operator
 */
public void onInfoChanged(AVIMClient client, AVIMConversation conversation, JSONObject attr,
                          String operator)

// Not supported yet

Notes:

You can either retrieve the properties being updated from the callback function or directly read the latest values from the Conversation object.

Retrieving Member Lists

To get the list of members in a conversation, we can call the method for fetching on a Conversation object and then get the result from it:

// fetch will trigger an operation to retrieve the latest data from the cloud
conversation.fetch().then(function(conversation) {
  console.log('members: ', conversation.members);
).catch(console.error.bind(console));

// fetchWithCallback will trigger an operation to retrieve the latest data from the cloud
[conversation fetchWithCallback:^(BOOL succeeded, NSError *error) {
    if (succeeded) {
        NSLog(@"", conversation.members);
    }
}];

// fetchInfoInBackground will trigger an operation to retrieve the latest data from the cloud
conversation.fetchInfoInBackground(new AVIMConversationCallback() {
  @Override
  public void done(AVIMException e) {
    if (e == null) {
      conversation.getMembers();
    }
  }
});

// Not supported yet

Notes:

You can only get member lists of basic conversations. Chat rooms and system conversations don't have member lists.

Querying Conversations with Custom Conditions

There are more ways to get a Conversation beside listening to incoming events. You might want your users to search chat rooms by the names or locations of them, or to look for conversations that has certain members in them. All these requirements can be satisfied with the help of queries.

Queries on ID

Here ID refers to the objectId in the _Conversation table. Since IDs are indexed, querying by ID is the easiest and most efficient way to look for a conversation:

tom.getConversation('551260efe4b01608686c3e0f').then(function(conversation) {
  console.log(conversation.id);
}).catch(console.error.bind(console));

AVIMConversationQuery *query = [tom conversationQuery];
[query getConversationById:@"551260efe4b01608686c3e0f" callback:^(AVIMConversation *conversation, NSError *error) {
    if (succeeded) {
        NSLog(@"Query completed!");
    }
}];

AVIMConversationsQuery query = tom.getConversationsQuery();
query.whereEqualTo("objectId","551260efe4b01608686c3e0f");
query.findInBackground(new AVIMConversationQueryCallback(){
    @Override
    public void done(List<AVIMConversation> convs,AVIMException e){
      if(e==null){
        if(convs!=null && !convs.isEmpty()){
          // convs.get(0) is the conversation being found
        }
      }
    }
});

var query = tom.GetQuery();
var conversation = await query.GetAsync("551260efe4b01608686c3e0f");

Querying by Conditions

LeanMessage offers a variety of ways for you to look for conversations that satisfy certain conditions.

Let's start with equalTo which is the simplest method for querying conversations. The code below looks for all the conversations that have type (a string field) to be private:

var query = client.getQuery();
query.equalTo('attr.type','private');
query.find().then(function(conversations) {
  // conversations contains all the results
}).catch(console.error.bind(console));

AVIMConversationQuery *query = [tom conversationQuery];
[query whereKey:@"attr.type" equalTo:@"private"];
// Perform query
[query findConversationsWithCallback:^(NSArray *objects, NSError *error) {
    NSLog(@"%ld conversations found!", [objects count]);
}];

AVIMConversationsQuery query = tom.getConversationsQuery();
query.whereEqualTo("attr.type","private");
// Perform query
query.findInBackground(new AVIMConversationQueryCallback(){
  @Override
  public void done(List<AVIMConversation> convs,AVIMException e){
    if(e == null){
      // convs contains all the results
    }
  }
});

// Since WhereXXX returns a new query instance each time, the code below will not work:
//   var query = tom.GetQuery();
//   query.WhereEqualTo("attr.type","private");
// You can use this way:
//   var query = tom.GetQuery();
//   query = query.WhereEqualTo("attr.type","private");
// This way is more recommended:
//   var query = tom.GetQuery().WhereEqualTo("attr.type","private");
var query = tom.GetQuery().WhereEqualTo("attr.type","private");
await query.FindAsync();

The interface for querying conversations is very similar to that for querying objects in LeanStorage. If you're already familiar with LeanStorage, it shouldn't be hard for you to learn how to query conversations:

You can get query results with find
You can get number of results with count
You can get the first conversation satisfying conditions with first
You can implement pagination with skip and limit

You can also apply conditions like "greater than", "greater than or equal to", "less than", and "less than or equal to" to Number and Date fields:

Logic	`ConversationQuery` Method
Equal to	`equalTo`
Not equal to	`notEqualTo`
Greater than	`greaterThan`
Greater than or equal to	`greaterThanOrEqualTo`
Less than	`lessThan`
Less than or equal to	`lessThanOrEqualTo`

Logic	`AVIMConversationQuery` Method
Equal to	`equalTo`
Not equal to	`notEqualTo`
Greater than	`greaterThan`
Greater than or equal to	`greaterThanOrEqualTo`
Less than	`lessThan`
Less than or equal to	`lessThanOrEqualTo`

Logic	`AVIMConversationQuery` Method
Equal to	`whereEqualTo`
Not equal to	`whereNotEqualsTo`
Greater than	`whereGreaterThan`
Greater than or equal to	`whereGreaterThanOrEqualsTo`
Less than	`whereLessThan`
Less than or equal to	`whereLessThanOrEqualsTo`

Logic	`AVIMConversationQuery` Method
Equal to	`WhereEqualTo`
Not equal to	`WhereNotEqualsTo`
Greater than	`WhereGreaterThan`
Greater than or equal to	`WhereGreaterThanOrEqualsTo`
Less than	`WhereLessThan`
Less than or equal to	`WhereLessThanOrEqualsTo`

Notes about default query conditions:

When querying conversations, if there isn't any where condition specified, ConversationQuery will look for conversations containing the current user by default. Such condition will be dismissed if any where condition is applied to the query. If you want to look for conversations containing certain clientId, you can follow the way introduced in Queries on Array Values to perform queries on m with the value of clientId. This won't cause any conflict with the default condition.

Using Regular Expressions

You can use regular expressions as conditions when querying with ConversationsQuery. For example, to look for all the conversations that have language to be Chinese:

query.matches('language',/[\\u4e00-\\u9fa5]/); // language is Chinese characters

[query whereKey:@"language" matchesRegex:@"[\u4e00-\u9fa5]"]; // language is Chinese characters

query.whereMatches("language","[\\u4e00-\\u9fa5]"); // language is Chinese characters

query.WhereMatches("language","[\\u4e00-\\u9fa5]"); // language is Chinese characters

Queries on String Values

You can look for conversations with string values that start with a particular string, which is similar to LIKE 'keyword%' in SQL. For example, to look for all conversations with names starting with education:

query.startsWith('name','education');

[query whereKey:@"name" hasPrefix:@"education"];

query.whereStartsWith("name","education");

query.WhereStartsWith("name","education");

You can also look for conversations with string values that include a particular string, which is similar to LIKE '%keyword%' in SQL. For example, to look for all conversations with names including education:

query.contains('name','education');

[query whereKey:@"name" containsString:@"education"];

query.whereContains("name","education");

query.WhereContains("name","education");

If you want to look for conversations with string values that exclude a particular string, you can use regular expressions. For example, to look for all conversations with names excluding education:

var regExp = new RegExp('^((?!education).)*{{body}}#39;, 'i');
query.matches('name', regExp);

[query whereKey:@"name" matchesRegex:@"^((?!education).)* $ "];

query.whereMatches("name","^((?!education).)* $ ");

query.WhereMatches("name","^((?!education).)* $ ");

Queries on Array Values

You can use containsAll, containedIn, and notContainedIn to perform queries on array values. For example, to look for all conversations containing Tom:

query.containedIn('m', ['Tom']);

[query whereKey:@"m" containedIn:@[@"Tom"]];

query.whereContainedIn("m", Arrays.asList("Tom"));

List<string> members = new List<string>();
members.Add("Tom");
query.WhereContainedIn("m", members);

Queries on Existence

You can look for conversations with or without certain fields to be empty. For example, to look for all conversations with lm to be empty:

query.doesNotExist('lm')

[query whereKeyDoesNotExist:@"lm"];

query.whereDoesNotExist("lm");

query.WhereDoesNotExist("lm");

Or, to look for all conversations with lm not to be empty:

query.exists('lm')

[query whereKeyExists:@"lm"];

query.whereExists("lm");

query.WhereExists("lm");

Compound Queries

To look for all conversations with age to be less than 18 and keywords containing education:

// Look for all conversations with `age` to be less than `18` and `keywords` containing `education`
query.contains('keywords', 'education').lessThan('age', 18);

[query whereKey:@"keywords" containsString:@"'education'"];
[query whereKey:@"age" lessThan:@(18)];

query.whereContains("keywords", "'education'");
query.whereLessThan("age", 18);

query.WhereContains("keywords", "'education'").WhereLessThan("age", 18);

You can also connect two queries with and or or to form a new query.

For example, to look for all conversations that either has age to be less than 18 or has keywords containing education:

// Not supported yet

AVIMConversationQuery *ageQuery = [tom conversationQuery];
[ageQuery whereKey:@"age" greaterThan:@(18)];

AVIMConversationQuery *keywordsQuery = [tom conversationQuery];
[keywordsQuery whereKey:@"keywords" containsString:@"education"];

AVIMConversationQuery *query = [AVIMConversationQuery orQueryWithSubqueries:[NSArray arrayWithObjects:ageQuery,keywordsQuery,nil]];

AVIMConversationsQuery ageQuery = tom.getConversationsQuery();
ageQuery.whereLessThan('age', 18);

AVIMConversationsQuery keywordsQuery = tom.getConversationsQuery();
keywordsQuery.whereContains('keywords', 'education');

AVIMConversationsQuery query = AVIMConversationsQuery.or(Arrays.asList(priorityQuery, statusQuery));

var ageQuery = tom.GetQuery().WhereLessThan('age', 18);

var keywordsQuery = tom.GetQuery().WhereContains('keywords', 'education').

var query = AVIMConversationQuery.or(new AVIMConversationQuery[] { ageQuery, keywordsQuery});

Sorting

You can sort the results of a query by ascending or descending order on certain fields. For example:

// Ascend by name and descend by creation time
query.addAscending('name').addDescending('createdAt');

AVIMClient *client = [[AVIMClient alloc] initWithClientId:@"Tom"];

[client openWithCallback:^(BOOL succeeded, NSError *error) {
    AVIMConversationQuery *query = [client conversationQuery];
    /* Descend by creation time */
    [query orderByDescending:@"createdAt"];
    [query findConversationsWithCallback:^(NSArray *conversations, NSError *error) {
        NSLog(@"%ld conversations found!", [conversations count]);
    }];
}];

AVIMClient tom = AVIMClient.getInstance("Tom");

tom.open(new AVIMClientCallback() {
  @Override
  public void done(AVIMClient client, AVIMException e) {
    if (e == null) {
      // Logged in
      AVIMConversationsQuery query = client.getConversationsQuery();

      // Descend by creation time
      query.orderByDescending("createdAt");

      query.findInBackground(new AVIMConversationQueryCallback() {
        @Override
        public void done(List<AVIMConversation> convs, AVIMException e) {
          if (e == null) {
            if(convs != null && !convs.isEmpty()) {
              // Get results
            }
          }
        }
      });
    }
  }
});

// Not supported yet

Excluding Member Lists from Results

When searching conversations, you can exclude the lists of members from query results if you don't need them. By doing so, their members fields will become empty arrays. This helps you improve the speed of your app and reduces the bandwidth needed.

query.compact(true);

AVIMClient *client = [[AVIMClient alloc] initWithClientId:@"Tom"];

[client openWithCallback:^(BOOL succeeded, NSError *error) {
    AVIMConversationQuery *query = [client conversationQuery];
    /* Exclude member lists from results */
    query.option = AVIMConversationQueryOptionCompact;
    [query findConversationsWithCallback:^(NSArray *conversations, NSError *error) {
        NSLog(@"%ld conversations found!", [conversations count]);
    }];
}];

public void queryConversationCompact() {
  AVIMClient tom = AVIMClient.getInstance("Tom");
  tom.open(new AVIMClientCallback() {
    @Override
    public void done(AVIMClient client, AVIMException e) {
      if (e == null) {
        // Logged in
        AVIMConversationsQuery query = client.getConversationsQuery();
        query.setCompact(true);
        query.findInBackground(new AVIMConversationQueryCallback() {
          @Override
          public void done(List<AVIMConversation> convs, AVIMException e) {
            if (e == null) {
              // Get results
            }
          }
        });
      }
    }
  });
}

// Not supported yet

Including Latest Messages in Results

Many chatting apps show the latest messages of conversations together in a list. If you want the similar function in your app, you can turn on the option when querying conversations:

// withLastMessagesRefreshed includes the latest messages of conversations in results
query.withLastMessagesRefreshed(true);

AVIMClient *client = [[AVIMClient alloc] initWithClientId:@"Tom"];

[client openWithCallback:^(BOOL succeeded, NSError *error) {
    AVIMConversationQuery *query = [client conversationQuery];
    /* Include the latest messages of conversations in results */
    query.option = AVIMConversationQueryOptionWithMessage;
    [query findConversationsWithCallback:^(NSArray *conversations, NSError *error) {
        NSLog(@"%ld conversations found!", [conversations count]);
    }];
}];

public void queryConversationWithLastMessage() {
  AVIMClient tom = AVIMClient.getInstance("Tom");
  tom.open(new AVIMClientCallback() {
    @Override
    public void done(AVIMClient client, AVIMException e) {
      if (e == null) {
        // Logged in
        AVIMConversationsQuery query = client.getConversationsQuery();
        /* Include the latest messages of conversations in results */
        query.setWithLastMessagesRefreshed(true);
        query.findInBackground(new AVIMConversationQueryCallback() {
          @Override
          public void done(List<AVIMConversation> convs, AVIMException e) {
            if (e == null) {
              // Get results
            }
          }
        });
      }
    }
  });
}

// Not supported yet

Keep in mind that what this option really does is to refresh the latest messages of conversations. Due to the existence of cache, it is still possible for you to retrieve the outdated "latest messages" even though you set the option to be false.

Caching Results

Conversations will be cached in memory using dictionaries according to their IDs. Such cache will not be persisted.

By caching query results locally, if the device is offline, or if the app is just opened and the request for synchronizing with cloud is not completed yet, there could still be some data available. You can also reduce the data usage of the user by performing queries with cloud only when the app is first opened and having subsequent queries completed with local cache.

Keep in mind that query results will be fed with local cache first and will be synchronized with the cloud right after that. The expiration time for cache is 1 hour. You can configure cache with the following methods provided by AVIMConversationQuery:

// Set caching policy; defaults to kAVCachePolicyCacheElseNetwork
@property (nonatomic) AVCachePolicy cachePolicy;

// Set expiration time; defaults to 1 hour (1 * 60 * 60)
@property (nonatomic) NSTimeInterval cacheMaxAge;

If you want cache to be accessed only when there's an error querying with the cloud, you can do this way:

AVIMConversationQuery *query = [[AVIMClient defaultClient] conversationQuery];
query.cachePolicy = kAVCachePolicyNetworkElseCache;
[query findConversationsWithCallback:^(NSArray *objects, NSError *error) {

}];

// Set caching policy for AVIMConversationsQuery
public void setQueryPolicy(AVQuery.CachePolicy policy);

If you want cache to be accessed only when there's an error querying with the cloud, you can do this way:

AVIMConversationsQuery query = client.getConversationsQuery();
query.setQueryPolicy(AVQuery.CachePolicy.NETWORK_ELSE_CACHE);
query.findInBackground(new AVIMConversationQueryCallback() {
  @Override
  public void done(List<AVIMConversation> conversations, AVIMException e) {

  }
});

Not supported yet.

Optimizing Performance

Since Conversation objects are stored on LeanStorage, you can make use of indexes to improve the efficiency of querying, just like how you would do to other classes. Here are some suggestions for optimizing performance:

By default, indexes are created for objectId, updatedAt, and createdAt of Conversation, so querying by these fields would be naturally fast.
Although it's possible to implement pagination with skip and limit, the speed would slow down when the dataset grows larger. It would be more efficient to make use of updatedAt or lastMessageAt instead.
When searching for conversations containing a certain user by using contains on m, it's recommended that you stick to the default limit (which is 10) and make use of updatedAt or lastMessageAt for pagination.
If you app has too many conversations, consider creating a cloud function that periodically cleans up inactive conversations.

Retrieving Messages

By default, message histories are stored on the cloud for 180 days. You may either pay to extend the period (contact us at support@leancloud.rocks) or synchronize them to your own server with REST API.

Our SDKs offer various of ways for you to retrieve message histories. iOS and Android SDKs also provide caching mechanism to help you reduce the number of queries you have to perform and display message histories to users even their devices are offline.

Retrieving Messages Chronologically (New to Old)

The most common way to retrieve messages is to fetch them from new to old with the help of pagination:

conversation.queryMessages({
  limit: 10, // limit could be any number from 1 to 1000 (defaults to 100)
}).then(function(messages) {
  // The last 10 messages ordered from old to new
}).catch(console.error.bind(console));

// Retrieve the last 10 messages; limit could be any number from 1 to 1000 (defaults to 100)
[conversation queryMessagesWithLimit:10 callback:^(NSArray *objects, NSError *error) {
    NSLog(@"Messages Retrieved!");
}];

// limit could be any number from 1 to 1000 (defaults to 100)
conv.queryMessages(10, new AVIMMessagesQueryCallback() {
  @Override
  public void done(List<AVIMMessage> messages, AVIMException e) {
    if (e == null) {
      // The last 10 messages retrieved
    }
  }
});

// limit could be any number from 1 to 1000 (defaults to 100)
var messages = await conversation.QueryMessageAsync(limit: 10);
foreach (var message in messages)
{
  if (message is AVIMTextMessage)
  {
    var textMessage = (AVIMTextMessage)message;
  }
}

Here queryMessage supports pagination. Given the fact that you can locate a single message with its messageId and timestamp, this means that you can retrieve the next few messages after a given message by providing the messageId and timestamp of that message:

// JS SDK encloses the feature into an iterator so you can keep retrieving new data by calling next
// Create an iterator and retrieve 10 messages each time
var messageIterator = conversation.createMessagesIterator({ limit: 10 });
// Call next for the first time and get the first 10 messages; done equals to false means that there are more messages
messageIterator.next().then(function(result) {
  // result: {
  //   value: [message1, ..., message10],
  //   done: false,
  // }
}).catch(console.error.bind(console));
// Call next for the second time and get the 11th to 20th messages; done equals to false means that there are more messages
// The iterator will keep track of the breaking point so you don't have to specify it
messageIterator.next().then(function(result) {
  // result: {
  //   value: [message11, ..., message20],
  //   done: false,
  // }
}).catch(console.error.bind(console));

// Retrieve the last 10 messages
[conversation queryMessagesWithLimit:10 callback:^(NSArray *messages, NSError *error) {
    NSLog(@"First retrieval completed!");
    // Get the messages right before the first message in the first page
    AVIMMessage *oldestMessage = [messages firstObject];
    [conversation queryMessagesBeforeId:oldestMessage.messageId timestamp:oldestMessage.sendTimestamp limit:10 callback:^(NSArray *messagesInPage, NSError *error) {
        NSLog(@"Second retrieval completed!");
    }];
}];

// limit could be any number from 1 to 1000 (defaults to 100)
conv.queryMessages(10, new AVIMMessagesQueryCallback() {
  @Override
  public void done(List<AVIMMessage> messages, AVIMException e) {
    if (e == null) {
      // The last 10 messages retrieved
      // The earliest message will be the first one
      AVIMMessage oldestMessage = messages.get(0);

      conv.queryMessages(oldestMessage.getMessageId(), oldestMessage.getTimestamp(),20,
          new AVIMMessageQueryCallback(){
            @Override
            public void done(List<AVIMMessage> messagesInPage,AVIMException e){
              if(e== null){
                // Query completed
                Log.d("Tom & Jerry", "got " + messagesInPage.size()+" messages ");
              }
          }
      });
    }
  }
});

// limit could be any number from 1 to 1000 (defaults to 100)
var messages = await conversation.QueryMessageAsync(limit: 10);
var oldestMessage = messages.ToList()[0];
var messagesInPage = await conversation.QueryMessageAsync(beforeMessageId: oldestMessage.Id, beforeTimeStamp: oldestMessage.ServerTimestamp);

Retrieving Messages by Types

Beside retrieving messages in time orders, you can also do that based on the types of messages. This could be helpful in scenarios like displaying all the images in a conversation.

queryMessage can take in the type of messages:

conversation.queryMessages({ type: ImageMessage.TYPE }).then(messages => {
  console.log(messages);
}).catch(console.error);

[conversation queryMediaMessagesFromServerWithType:kAVIMMessageMediaTypeImage limit:10 fromMessageId:nil fromTimestamp:0 callback:^(NSArray *messages, NSError *error) {
    if (!error) {
        NSLog(@"Query completed!");
    }
}];

int msgType = .AVIMMessageType.IMAGE_MESSAGE_TYPE;
conversation.queryMessagesByType(msgType, limit, new AVIMMessagesQueryCallback() {
    @Override
    public void done(List<AVIMMessage> messages, AVIMException e){
    }
});

// Pass in a generic type parameter and the SDK will automatically read the type and send it to the server for searching messages
var imageMessages = await conversation.QueryMessageAsync<AVIMImageMessage>();

To retrieve more images, follow the way introduced in the previous section to go through different pages.

Retrieving Messages Chronologically (Old to New)

Beside the two ways mentioned above, you can also retrieve messages from old to new. The code below shows how you can retrieve messages starting from the time the conversation is created:

var { MessageQueryDirection } = require('leancloud-realtime');
conversation.queryMessages({
  direction: MessageQueryDirection.OLD_TO_NEW,
}).then(function(messages) {
  // Handle result
}.catch(function(error) {
  // Handle error
});

[conversation queryMessagesInInterval:nil direction:AVIMMessageQueryDirectionFromOldToNew limit:20 callback:^(NSArray<AVIMMessage *> * _Nullable messages, NSError * _Nullable error) {
    if (messages.count) {
        // Handle result
    }
}];

AVIMMessageInterval interval = new AVIMMessageInterval(null, null);
conversation.queryMessages(interval, AVIMMessageQueryDirectionFromOldToNew, limit,
  new AVIMMessagesQueryCallback(){
    public void done(List<AVIMMessage> messages, AVIMException exception) {
      // Handle result
    }
});

var earliestMessages = await conversation.QueryMessageAsync(direction: 0);

It is a bit more complicated to implement pagination with this method. See the next section for more explanations.

Retrieving Messages Chronologically (From a Timestamp to a Direction)

You can retrieve messages starting from a given message (determined by ID and timestamp) toward a certain direction:

New to old: Retrieve messages sent before a given message
Old to new: Retrieve messages sent after a given message

Now we can implement pagination on different directions.

var { MessageQueryDirection } = require('leancloud-realtime');
conversation.queryMessages({
  startTime: timestamp,
  startMessageId: messageId,
startClosed: false,
  direction: MessageQueryDirection.OLD_TO_NEW,
}).then(function(messages) {
  // Handle result
}.catch(function(error) {
  // Handle error
});

AVIMMessageIntervalBound *start = [[AVIMMessageIntervalBound alloc] initWithMessageId:nil timestamp:timestamp closed:false];
AVIMMessageInterval *interval = [[AVIMMessageInterval alloc] initWithStartIntervalBound:start endIntervalBound:nil];
[conversation queryMessagesInInterval:interval direction:direction limit:20 callback:^(NSArray<AVIMMessage *> * _Nullable messages, NSError * _Nullable error) {
    if (messages.count) {
        // Handle result
    }
}];

AVIMMessageIntervalBound start = AVIMMessageInterval.createBound(messageId, timestamp, false);
AVIMMessageInterval interval = new AVIMMessageInterval(start, null);
AVIMMessageQueryDirection direction;
conversation.queryMessages(interval, direction, limit,
  new AVIMMessagesQueryCallback(){
    public void done(List<AVIMMessage> messages, AVIMException exception) {
      // Handle result
    }
});

var earliestMessages = await conversation.QueryMessageAsync(direction: 0, limit: 1);
// Get messages sent after earliestMessages.Last()
var nextPageMessages = await conversation.QueryMessageAfterAsync(earliestMessages.Last());

Retrieving Messages Within a Period of Time

Beside retrieving messages chronologically, you can also retrieve messages within a period of time. For example, if you already have two messages, you can have one of them to be the starting point and another one to be the ending point to retrieve all the messages between them:

Note: The limit of 100 messages per query still applies here. To fetch more messages, keep changing the starting point or the ending point until all the messages are retrieved.

conversation.queryMessages({
  startTime: timestamp,
  startMessageId: messageId,
  endTime: endTimestamp,
  endMessageId: endMessageId,
}).then(function(messages) {
  // Handle result
}.catch(function(error) {
  // Handle error
});

AVIMMessageIntervalBound *start = [[AVIMMessageIntervalBound alloc] initWithMessageId:nil timestamp:startTimestamp closed:false];
    AVIMMessageIntervalBound *end = [[AVIMMessageIntervalBound alloc] initWithMessageId:nil timestamp:endTimestamp closed:false];
AVIMMessageInterval *interval = [[AVIMMessageInterval alloc] initWithStartIntervalBound:start endIntervalBound:end];
[conversation queryMessagesInInterval:interval direction:direction limit:100 callback:^(NSArray<AVIMMessage *> * _Nullable messages, NSError * _Nullable error) {
    if (messages.count) {
        // Handle result
    }
}];

AVIMMessageIntervalBound start = AVIMMessageInterval.createBound(messageId, timestamp, false);
AVIMMessageIntervalBound end = AVIMMessageInterval.createBound(endMessageId, endTimestamp, false);
AVIMMessageInterval interval = new AVIMMessageInterval(start, end);
AVIMMessageQueryDirection direction;
conversation.queryMessages(interval, direction, limit,
  new AVIMMessagesQueryCallback(){
    public void done(List<AVIMMessage> messages, AVIMException exception) {
      // Handle result
    }
});

var earliestMessage = await conversation.QueryMessageAsync(direction: 0, limit: 1);
var latestMessage = await conversation.QueryMessageAsync(limit: 1);
// messagesInInterval can get at most 100 messages
var messagesInInterval = await conversation.QueryMessageInIntervalAsync(earliestMessage.FirstOrDefault(), latestMessage.FirstOrDefault());

Caching Messages

iOS and Android SDKs come with the mechanism that automatically caches all the messages received and retrieved on the local device (not supported by JavaScript or C# SDKs). It provides the following benefits:

Message histories can be viewed even devices are offline
The frequency of querying and the consumption of data can be minimized
The speed for viewing messages can be increased

Caching is enabled by default. You can turn it off with the following interface:

// Not supported yet

// Need to be set before calling [avimClient openWithCallback:callback]
avimClient.messageQueryCacheEnabled = false;

// Need to be set before calling AVIMClient.open(callback)
AVIMClient.setMessageQueryCacheEnable(false)

// Not supported yet

Logging out and Network Changes

Logging out

If your app allows users to log out, you can use the close method provided by AVIMClient to properly close the connection to the cloud:

tom.close().then(function() {
  console.log('Tom logged out.');
}).catch(console.error.bind(console));

[tom closeWithCallback:^(BOOL succeeded, NSError * _Nullable error) {
    if (succeeded) {
        NSLog(@"Logged out.");
    }
}];

tom.close(new AVIMClientCallback(){
    @Override
    public void done(AVIMClient client,AVIMException e){
        if(e==null){
            // Logged out
        }
    }
});

await tom.CloseAsync();

After the function is called, the connection between the client and the server will be terminated. If you check the status of the corresponding clientId on the cloud, it would show as "offline".

Network Changes

The availability of the messaging service is highly dependent on the Internet connection. If the connection is lost, all the operations regarding messages and conversations will fail. At this time, there needs to be some indicators on the UI to tell users about the network status.

Our SDKs maintain a heartbeat mechanism with the cloud which detects the change of network status and have your app notified if certain events occur. To be specific, if the connection status changes (becomes lost or recovered), the following events will be populated:

DISCONNECT: Connection to the server is lost. The messaging service is unavailable at this time.
OFFLINE: Network is unavailable.
ONLINE: Network is recovered.
SCHEDULE: Scheduled to reconnect after a period of time. The messaging service is still unavailable at this time.
RETRY: Reconnecting.
RECONNECT: Connection to the server is recovered. The messaging service is available at this time.

var { Event } = require('leancloud-realtime');

realtime.on(Event.DISCONNECT, function() {
  console.log('Connection to the server is lost.');
});
realtime.on(Event.OFFLINE, function() {
  console.log('Network is unavailable.');
});
realtime.on(Event.ONLINE, function() {
  console.log('Network is recovered.');
});
realtime.on(Event.SCHEDULE, function(attempt, delay) {
  console.log('Reconnecting in ' + delay + ' ms as attempt ' + (attempt + 1) + '.');
});
realtime.on(Event.RETRY, function(attempt) {
  console.log('Reconnecting as attempt ' + (attempt + 1) + '.');
});
realtime.on(Event.RECONNECT, function() {
  console.log('Connection to the server is recovered.');
});

The following events will be populated on AVIMClientDelegate:

imClientPaused:(AVIMClient *)imClient occurs when the connection is lost. The messaging service is unavailable at this time.
imClientResuming:(AVIMClient *)imClient occurs when trying to reconnect. The messaging service is still unavailable at this time.
imClientResumed:(AVIMClient *)imClient occurs when the connection is recovered. The messaging service is available at this time.

The following events will be populated on AVIMClientEventHandler:

onConnectionPaused() occurs when the connection is lost. The messaging service is unavailable at this time.
onConnectionResume() occurs when the connection is recovered. The messaging service is available at this time.
onClientOffline() occurs when single device sign-on is enabled and the current device is forced to go offline.

The following events will be populated on AVRealtime:

OnDisconnected occurs when the connection is lost. The messaging service is unavailable at this time.
OnReconnecting occurs when trying to reconnect. The messaging service is still unavailable at this time.
OnReconnected occurs when the connection is recovered. The messaging service is available at this time.
OnReconnectFailed occurs when it fails to reconnect. The messaging service is unavailable at this time.

More Suggestions

Sorting Conversations by Last Activities

In many scenarios you may need to sort conversations based on the time the last message in each of them is sent. Here we offer a property lastMessageAt for each AVIMConversation (lm in the _Conversation table) which dynamically changes to reflect the time of the last message. The time is server-based (accurate to a second) so you don't have to worry about the time on the clients. AVIMConversation also offers a method for you to retrieve the last message of each conversation, which gives you more flexibility to design the UI of your app.

Auto Reconnecting

If the connection between a client and the cloud is not properly closed, our iOS and Android SDKs will automatically reconnect when the network is recovered. You can listen to IMClient to get updated about the network status.

More Conversation Types

Beside the one-on-one chatting and group chats mentioned earlier, LeanMessage also supports these types of conversations:

Chat room: This can be used to build conversations that serve scenarios like live streaming. It's different than a basic group chat on the number of members supported and the deliverability promised. See 3. Chat Rooms for more details.
Temporary conversation: This can be used to build conversations between users and customer service representatives. It's different than a basic one-on-one chatting on the fact that it has a shorter TTL which brings higher flexibility and lower cost (on data storage). See 3. Temporary Conversations for more details.
System conversation: This can be used to build accounts that could broadcast messages to all their subscribers. It's different than a basic group chat on the fact that users can subscribe to it and there isn't a number limit of members. Subscribers can also send one-on-one messages to these accounts and these messages won't be seen by other users. See 4. System Conversations for more details.

Continue Reading

2. Advanced Messaging Features, Push Notifications, Synchronization, and Multi Device Sign-on

3. Security, Permission Management, Chat Rooms, and Temporary Conversations

4. Hooks and System Conversations