Sending and Receiving Messages (Android)

Last updated: 2020-10-21 11:09:20

    Message Classification

    IM messages are classified by message destination into two types: one-to-one messages (also called C2C messages) and group messages.

    Message Type API Keyword Description
    C2C message C2CMessage When sending a C2C message, you must specify the UserID of the message recipient, and only the recipient can receive this message.
    Group message GroupMessage When sending a group message, you must specify the groupID of the target group, and all users in this group can receive this message.

    IM messages can also be classified by content into text messages, custom (signaling) messages, image messages, video messages, voice messages, file messages, location messages, and group tips.

    Message Type API Keyword Description
    Text message TextElem It refers to a common text message. Sensitive words in text messages will be filtered out in the IM service. If a message containing sensitive words is sent, the 80001 error code is returned.
    Custom message CustomElem It is a section of the binary buffer, which is often used to transfer custom signaling in your app. Its content is not filtered for sensitive words.
    Image message ImageElem When the IM SDK sends an original image, it automatically generates two thumbnails of different sizes. The three images are called the original image, large image, and thumbnail, respectively.
    Video message VideoElem A video message contains a video file and a thumbnail.
    Voice message SoundElem The feature of displaying a red dot upon playback of the voice message is supported.
    File message FileElem The maximum size of a file message is 100 MB.
    Location message LocationElem A location message contains three fields: location description, longitude, and latitude.
    Group tip GroupTipsElem A group tip is often used to carry a system notification in a group, for example, a notification indicating that a member joins or quits the group, the group description is modified, or the profile of a group member is changed.

    Sending and Receiving a Simple Message

    V2TIMManager provides a set of simple APIs for sending and receiving messages. Although these APIs can be used to send or receive text messages and custom (signaling) messages, they are easy to use and only a few minutes are needed to complete interfacing.

    Sending text and signaling messages (simplified APIs)

    To send text messages, call sendC2CTextMessage or sendGroupTextMessage. Text messages will be filtered by IM for sensitive words. If a message containing sensitive words is sent, the 80001 error code is returned. To send C2C custom (signaling) messages, call sendC2CCustomMessage or sendGroupCustomMessage. A custom message is essentially a section of the binary buffer, and is often used to transfer custom signaling in your app. Its content is not filtered for sensitive words.

    Receiving text and signaling messages (simplified APIs)

    To listen to simple text and signaling messages, call addSimpleMsgListener. To listen to complex image, video, and voice messages, call addAdvancedMsgListener defined in V2TIMMessageManager.

    Note:

    Do not use addSimpleMsgListener together with addAdvancedMsgListener. Otherwise, logic bugs may occur.

    Typical example: sending and receiving on-screen comments in a livestreaming group

    In the livestreaming scenario, it is a common way of communication to send or receive on-screen comments in a livestreaming group. This can be easily implemented through the simple message APIs.

    1. The anchor can call createGroup to create a livestreaming group (AVChatRoom) and record the group ID in the list of rooms in "Broadcasting" state.
    2. A viewer can select an anchor that he/she likes, and call joinGroup to join the AVChatRoom created by this anchor.
    3. The message sender can call sendGroupTextMessage to send a group text message as the on-screen comment.
    4. The message recipient can call addSimpleMsgListener to register a simple message listener, and use the listener callback function onRecvGroupTextMessage to obtain text messages.

    "FlyHeart" is an instruction. To configure the "FlyHeart" feature for an AVChatRoom, perform the steps below:

    1. Define a custom message type, for example, a JSON string { "command": "favor", "value": 101 }.
    2. Call sendGroupCustomMessage to send a message, and call onRecvGroupCustomMessage to receive the message.

    Sending and Receiving Rich Media Messages

    Image, video, voice, file, and location messages are called rich media messages. Compared with simple messages, it is more complex to send or receive rich media messages.

    • Before sending a rich media message, use the create function to create a V2TIMMessage object. Then, call the corresponding send API to send this message.
    • When receiving the rich media message, check elemType and perform secondary parsing on Elem obtained based on elemType.

    Sending Rich Media Messages

    The following takes an image message as an example to describe the process of sending a rich media message.

    1. The sender calls createImageMessage to create an image message, and obtain the V2TIMMessage message object.
    2. The sender calls sendMessage to send the created message object.

    Receiving Rich Media Messages

    1. The recipient calls addAdvancedMsgListener to set the advanced message listener.
    2. The recipient obtains the image message V2TIMMessage through the listener callback onRecvNewMessage.
    3. The recipient parses elemType in V2TIMMessage, and performs secondary parsing based on the message type to obtain the content of Elem in the message.

    Typical example: sending and receiving image messages

    The sender creates and sends an image message.

    // Create an image message.
    V2TIMMessage v2TIMMessage = V2TIMManager.getMessageManager().createImageMessage("/sdcard/test.png");
    // Send the image message.
    V2TIMManager.getMessageManager().sendMessage(v2TIMMessage, "toUserID", null, V2TIMMessage.V2TIM_PRIORITY_DEFAULT, false, null,  new V2TIMSendCallback<V2TIMMessage>() {
        @Override
        public void onError(int code, String desc) {
            // The image message fails to be sent.
        }
        @Override
        public void onSuccess(V2TIMMessage v2TIMMessage) {
            // The image message is successfully sent.
        }
        @Override
        public void onProgress(int progress) {
            // Image upload progress (0-100)
        }
    });

    The recipient identifies the image message, and parses the message to obtain the original image, large image, and thumbnail contained in the message.

    @Override
    public void onRecvNewMessage(V2TIMMessage msg) {
        int elemType = msg.getElemType();
        if (elemType == V2TIMMessage.V2TIM_ELEM_TYPE_IMAGE) {
            V2TIMImageElem v2TIMImageElem = msg.getImageElem();
            // An image message contains an image in three different sizes: original image, large image, and thumbnail. (The SDK automatically generates the large image, and thumbnail.)
            - A large image is an image obtained after the original image is proportionally compressed. After the compression, the smaller one of the height and width is equal to 720 pixels.
            - A thumbnail is an image obtained after the original image is proportionally compressed. After the compression, the smaller one of the height and width is equal to 198 pixels.
            List<V2TIMImageElem.V2TIMImage> imageList = v2TIMImageElem.getImageList();
                for (V2TIMImageElem.V2TIMImage v2TIMImage : imageList) {
                    String uuid = v2TIMImage.getUUID(); // Image ID
                    int imageType = v2TIMImage.getType(); // Image type
                    int size = v2TIMImage.getSize(); // Image size (bytes)
                    int width = v2TIMImage.getWidth(); // Image width
                    int height = v2TIMImage.getHeight(); // Image height
                    // Set the image download path `imagePath`. Here, `uuid` can be used as an identifier to avoid repeated download.
                    String imagePath = "/sdcard/im/image/" + "myUserID" + uuid;
                    File imageFile = new File(imagePath);
                    if (imageFile.exists()) {
                        v2TIMImage.downloadImage(imagePath, new V2TIMDownloadCallback() {
                            @Override
                            public void onProgress(V2TIMElem.V2ProgressInfo progressInfo) {
                                // Image download progress. `v2ProgressInfo.getCurrentSize()` indicates the downloaded size, and `v2ProgressInfo.getTotalSize()` indicates the total file size.
                            }
                            @Override
                            public void onError(int code, String desc) {
                                // The image fails to be downloaded.
                            }
                            @Override
                            public void onSuccess() {
                                // The image download is completed.
                            }
                        });
                } else {
                    // The image already exists.
                }
            }   
        }
    }

    Note:

    For more information on the message parsing sample code, see FAQs > 5. How can I parse different types of messages.

    Sending and Receiving Group @ Messages

    For a group @ message, the sender can listen to the input of the @ character in the input bar and call the group member selection interface. After selection is completed, the format "@A @B @C......" is displayed in the input box, and then the sender can continue to edit the message content and send the message. On the group chat list of the recipient’s conversation interface, the identifier "someone@me" or "@all members" will be displayed to remind the user that the user was mentioned by someone in the group.

    Note:

    Currently, only text @ messages are supported.

    Sending group @ messages

    1. The sender listens to the text input box on the chat interface and launches the group member selection interface. After selection is completed, the ID and nickname of the selected member are returned. The ID is used to construct the message object V2TIMMessage, and the nickname is displayed in the text box.
    2. The sender calls createTextAtMessage of V2TIMMessageManager to create an @ text message and obtain the message object V2TIMMessage.
    3. The sender calls sendMessage to send the created @ message object.

    Receiving group @ messages

    1. During conversation loading and update, the getGroupAtInfoList API of V2TIMConversation needs to be called to obtain the @ data list of the conversation.
    2. Through the getAtType API of the V2TIMGroupAtInfo object in the list, the @ data type is obtained and updated to the @ information of the current conversation.

    Typical examples: sending and receiving group @ messages

    • Sending a group @ message:
      The sender creates a group @ message and sends it:

      // Obtain the group member ID data.
      List<String> atUserList = updateAtUserList(mTextInput.getMentionList(true));
      // Create a group @ message.
      V2TIMMessage v2TIMMessage = V2TIMManager.getMessageManager().createTextAtMessage(message, atUserList);
      // Send the group @ message.
      V2TIMManager.getMessageManager().sendMessage(v2TIMMessage, null, "toGroupID",  V2TIMMessage.V2TIM_PRIORITY_DEFAULT, false, null,  new V2TIMSendCallback<V2TIMMessage>() {
        @Override
        public void onError(int code, String desc) {
            // The group @ message failed to be sent.
        }
        @Override
        public void onSuccess(V2TIMMessage v2TIMMessage) {
            // The group @ message was sent successfully.
        }
        @Override
        public void onProgress(int progress) {
      
        }
      });
    • Receiving a group @ message:
      During conversation loading and update, obtain the group @ data list:

    boolean atMe = false;
    boolean atAll = false;
    // Obtain the group @ data list.
    List<V2TIMGroupAtInfo> atInfoList = conversation.getGroupAtInfoList();
    if (atInfoList == null || atInfoList.isEmpty()){
        return V2TIMGroupAtInfo.TIM_AT_UNKNOWN;
    }
    // Obtain the @ data type.
    for(V2TIMGroupAtInfo atInfo : atInfoList){
        if (atInfo.getAtType() == V2TIMGroupAtInfo.TIM_AT_ME){
            atMe = true;
            continue;
        }
        if (atInfo.getAtType() == V2TIMGroupAtInfo.TIM_AT_ALL){
            atAll = true;
            continue;
        }
    }
    
    if (atAll && atMe){
        atInfoType = V2TIMGroupAtInfo.TIM_AT_ALL_AT_ME;
    } else if (atAll){
        atInfoType = V2TIMGroupAtInfo.TIM_AT_ALL;
    } else if (atMe){
        atInfoType = V2TIMGroupAtInfo.TIM_AT_ME;
    } else {
        atInfoType = V2TIMGroupAtInfo.TIM_AT_UNKNOWN;
    }
    // Update the @ type to the current conversation.
    switch (atInfoType){
        case V2TIMGroupAtInfo.TIM_AT_ME:
            Log.d(TAG, "update to the current conversation to display [someone@me]");
            break;
        case V2TIMGroupAtInfo.TIM_AT_ALL:
            Log.d(TAG, "update to the current conversation to display [@all members]");
            break;
        case V2TIMGroupAtInfo.TIM_AT_ALL_AT_ME:
            Log.d(TAG, "update to the current conversation to display [someone@me][@all members]");
            break;
        default:
            break;
    
    }

    Setting Offline Push (offlinePushInfo)

    When the recipient's app is killed, the IM SDK cannot receive new messages through the normal network connection. In this scenario, the offline push service provided by mobile phone manufacturers must be used to notify the recipient of new messages. For more information, see Offline Push (Android).

    Setting the title and content for offline push

    When sending messages, you can use the offlinePushInfo field in the sendMessage API to set the title and content for offline push.

    // Create and send a text message to groupA, and customize the title and content for offline push.
    V2TIMMessage v2TIMMessage = V2TIMManager.getMessageManager().createTextMessage(content);
    V2TIMOfflinePushInfo v2TIMOfflinePushInfo = new V2TIMOfflinePushInfo();
    // Set the title of the notification bar.
    v2TIMOfflinePushInfo.setTitle("offline_title");
    // Set the content of the notification bar.
    v2TIMOfflinePushInfo.setDesc("offline_desc");
    // Send a message.
    V2TIMManager.getMessageManager().sendMessage(v2TIMMessage, null, "groupA", V2TIMMessage.V2TIM_PRIORITY_DEFAULT, false,  v2TIMOfflinePushInfo, new V2TIMSendCallback<V2TIMMessage>() {
        @Override
        public void onError(int code, String desc) {
            // The message failed to be sent.
        }
        @Override
        public void onSuccess(V2TIMMessage v2TIMMessage) {
            // The message is sent successfully.
        }
        @Override
        public void onProgress(int progress) {
        }
    });

    Clicking a pushed message to go to the corresponding chat window

    To implement this feature, the sender needs to set ext, which is the extended field of the offline push object offlinePushInfo, when sending a message. When the recipient opens the app, the recipient can obtain ext by using different methods provided by mobile phone vendors for obtaining custom content, and then go to the corresponding chat window based on the content of ext.

    The following example assumes that Denny sends a message to Vinson.
    Sender: Denny needs to set ext before sending a message.

    // Denny sets `offlinePushInfo` and specifies `ext` before sending a message.
    JSONObject jsonObject = new JSONObject();
    try{
        jsonObject.put("action", "jump to denny");
    } catch (JSONException e) {
        e.printStackTrace();
    }
    String extContent = jsonObject.toString();
    V2TIMOfflinePushInfo v2TIMOfflinePushInfo = new V2TIMOfflinePushInfo();
    v2TIMOfflinePushInfo.setExt(extContent.getBytes());
    
    V2TIMManager.getMessageManager().sendMessage(v2TIMMessage, "vinson", null, V2TIMMessage.V2TIM_PRIORITY_DEFAULT, false,  v2TIMOfflinePushInfo, new V2TIMSendCallback<V2TIMMessage>() {
        @Override
        public void onError(int code, String desc) {}
        @Override
        public void onSuccess(V2TIMMessage v2TIMMessage) {}
        @Override
        public void onProgress(int progress) {}
    });

    Recipient: although Vinson's app is not online, it can still receive the notification message pushed offline by mobile phone vendors (for example, OPPO). When Vinson clicks the pushed message, the app is started.

    // After starting the app, Vinson obtains the custom content from the opened `Activity`.
    Bundle bundle = intent.getExtras();
    Set<String> set = bundle.keySet();
    if (set != null) {
        for (String key : set) {
            // key and value correspond to extKey and ext content set in Step 1.
            String value = bundle.getString(key);
            if (value.equals("jump to denny")) {
                // Go to the chat window with Denny.
                ...
            }
        }
    }

    Setting onlineUserOnly so that Messages Can Be Received Only Online

    In some scenarios, you may wish that sent messages can only be received by online users, that is, a recipient is not aware of the message when the recipient is offline. For this purpose, you can set onlineUserOnly to true when calling sendMessage. After the setting, the sent messages differ from common messages in the following ways:

    • Messages cannot be stored offline. That is, the recipient cannot receive messages unless he/she is online.
    • Messages do not support multi-device roaming. That is, if the recipient has received messages on one terminal, these messages cannot be received on any other terminal no matter whether these messages are read or not.
    • Messages cannot be stored locally. That is, these messages cannot be retrieved from the local history messages in the cloud.

    Typical example: displaying "The other party is typing...
    In the one-to-one chat scenario, you can call sendMessage to send the "I am typing..." message. When the recipient receives this message, "The other party is typing..." is displayed on the UI. The sample code is as follows:

    // Sending the "I am typing..." message to userA.
    JSONObject jsonObject = new JSONObject();
    try{
        jsonObject.put("command", "textInput");
    } catch (JSONException e) {
        e.printStackTrace();
    }
    V2TIMMessage v2TIMMessage = V2TIMManager.getMessageManager().createCustomMessage(jsonObject.toString().getBytes());
    V2TIMManager.getMessageManager().sendMessage(v2TIMMessage, "userA", null, V2TIMMessage.V2TIM_PRIORITY_DEFAULT, true,  v2TIMOfflinePushInfo, new V2TIMSendCallback<V2TIMMessage>() {
        @Override
        public void onError(int code, String desc) {}
        @Override
        public void onSuccess(V2TIMMessage v2TIMMessage) {}
        @Override
        public void onProgress(int progress) {}
    });

    Recalling Messages

    The sender can call the revokeMessage API to recall a successfully sent message. By default, the sender can recall a message that is sent within 2 minutes. You can change the time limit for message recall. For detailed operations, see Message recall settings.
    Message recall requires cooperation of the UI code at the recipient side. When the sender recalls a message, the recipient will receive a message recall notification, onRecvMessageRevoked. This notification contains the msgID of the recalled message. Based on this msgID, you can identify the message that has been recalled and change the corresponding message bubble to the "Message recalled" state on the UI.

    The sender recalls a message

    V2TIMManager.getMessageManager().revokeMessage(v2TIMMessage, new V2TIMCallback() {
        @Override
        public void onError(int code, String desc) {
            // The message fails to be recalled.
        }
        @Override
        public void onSuccess() {
            // The message is successfully recalled.
        }
    });

    The recipient learns that the message is recalled

    1. Call addAdvancedMsgListener to set the advanced message listener.
    2. Call onRecvMessageRevoked to receive the message recall notification.
    @Override
    public void onRecvMessageRevoked(String msgID) {
        // `msgList` is the message list on the current chat window.
        for (V2TIMMessage msg : msgList) {
            if (msg.getMsgID().equals(msgID)) {
                    // `msg` is the recalled message. You need to change the corresponding message bubble state on the UI.
            }
        }
    }

    Adding Read Receipts for Messages

    In the one-to-one chat scenario, when the recipient calls the markC2CMessageAsRead API to mark an incoming message as read, the message sender will receive a read receipt, indicating that the recipient has read his/her message.

    Note:

    Currently, only one-to-one chats support the read receipt feature, and group chats do not support this feature. Although the markGroupMessageAsRead API is also available in group chats, the group message senders currently cannot receive any read receipts.

    The recipient marks messages as read

     // Mark messages coming from Haven as read.
     V2TIMManager.getMessageManager().markC2CMessageAsRead("haven", new V2TIMCallback() {
        @Override
        public void onError(int code, String desc) {
            // Messages fail to be marked as read.
        }
        @Override
        public void onSuccess() {
            // Messages are successfully marked as read.
        }
    });

    The sender learns that the messages are read

    The event notification of the message receipt is located in the advanced message listener V2TIMAdvancedMsgListener. To learn that the message is already read, the sender must call addAdvancedMsgListener to set the listener. Then, the sender can receive a read receipt from the recipient through the onRecvC2CReadReceipt callback.

    @Override
    public void onRecvC2CReadReceipt(List<V2TIMMessageReceipt> receiptList) {
        // The sender may receive multiple read receipts at a time. Therefore, the array callback mode is used here.
        for (V2TIMMessageReceipt v2TIMMessageReceipt : receiptList) {
            // Message receiver
            String userID = v2TIMMessageReceipt.getUserID();
            // Time of the read receipt. A message is considered as read if the timestamp in the chat window is not later than `timestamp` here.
            long timestamp = v2TIMMessageReceipt.getTimest
        }
    }

    Viewing History Messages

    You can call getC2CHistoryMessageList to obtain history messages of one-to-one chats, or call getGroupHistoryMessageList to obtain history messages of group chats. If the network connection of the current device is normal, the IM SDK pulls history messages from the server by default. If the network connection is unavailable, the IM SDK directly reads history messages from the local database.

    Pulling history messages by page

    The IM SDK supports the feature of pulling history messages by page. The number of messages pulled per page cannot be too large; otherwise, the pulling speed is affected. We recommend that you pull 20 messages per page.
    The following example assumes that history messages of groupA are pulled by page, and the number of messages per page is 20. The sample code is as follows:

    // The value `null` of `lastMsg` is passed in for the first pulling, indicating that starting from the latest message, a total of 20 messages are pulled.
    V2TIMManager.getMessageManager().getGroupHistoryMessageList("groupA", 20, null, new V2TIMValueCallback<List<V2TIMMessage>>() {
        @Override
        public void onError(int code, String desc) {
            // Failed to pull
        }
        @Override
        public void onSuccess(List<V2TIMMessage> v2TIMMessages) {
            // Messages that are pulled by page are listed from new to old by default.
            if (v2TIMMessages.size() > 0) {
                // Obtain the start message for the next pulling by page.
                V2TIMMessage lastMsg = v2TIMMessages.get(v2TIMMessages.size() - 1);
                // Pull the remaining 20 messages.
                V2TIMManager.getMessageManager().getGroupHistoryMessageList("groupA", 20, lastMsg, new V2TIMValueCallback<List<V2TIMMessage>>() {
                    @Override
                    public void onError(int code, String desc) {
                         // Messages fail to be pulled.
                    }
    
                    @Override
                    public void onSuccess(List<V2TIMMessage> v2TIMMessages) {
                        // Message pulling is completed.
                    }
                });
            }
        }
    });

    In actual scenarios, pulling by page is often triggered by your swipe operation. Each time when you swipe on the message list, pulling by page is triggered once. However, the principle is similar to the preceding sample code. In either case, lastMsg specifies the start message for pulling, and count specifies the number of messages pulled each time.

    Precautions

    • The storage period of history messages is as follows:
      • Trial edition: free storage for 7 days, no extension supported.
      • Pro edition: free storage for 7 days, extension supported.
      • Flagship edition: free storage for 30 days, extension supported.
      It is a value-added service to extend the storage period of history messages. You can log in to the IM console to modify the relevant configuration. For more information about billing, see Value-added Service Pricing.
    • Only the meeting group (corresponding to the ChatRoom of the earlier version) supports pulling history messages of members before members join the group.
    • Messages in the AVChatRoom do not support local storage and multi-device roaming. Therefore, the getGroupHistoryMessageList API does not take effect on an AVChatRoom.

    Deleting Messages

    You can call the deleteMessages API to delete historical messages. After deletion, historical messages cannot be recovered.

    Setting Message Permissions

    Allowing message sending and receiving only among friends

    By default, the IM SDK does not prevent message sending and receiving among strangers. If you wish that C2C messages can be sent or received only among friends, you can log in to the IM console, choose Feature Configuration > Login and Messages > Relationship Check, and enable Check Relationship for One-to-One Messages. After this feature is enabled, you can send messages only to friends. When you try to send messages to strangers, the IM SDK returns the 20009 error code.

    Blocking messages from a specified user

    If you want to block messages from a specified user, call the addToBlackList API to add this user to the blocklist.
    When a user is added to the blocklist, the user does not know that he/she is in the blocklist by default. That is, after this user sends a message, the prompt still indicates that the message is sent successfully, but in fact the recipient will not receive the message. If you want a user in the blocklist to know that his/her message fails to be sent, you can log in to the IM console, choose Feature Configuration > Login and Messages > Blocklist Check, and disable Show "Sent successfully" After Sending Messages. After this feature is disabled, the IM SDK will return the 20007 error code when a user in the blocklist sends a message.

    Blocking messages from a specified group

    To block messages from a specified group, you can call the setReceiveMessageOpt API to set the group message receiving option to the V2TIM_GROUP_NOT_RECEIVE_MESSAGE state.

    Filtering Sensitive Words

    Text messages sent by the IM SDK are filtered by IM for sensitive words. If a sent text message contains sensitive words, the IM SDK will return the 80001 error code.

    FAQs

    1. Why am I receiving duplicate messages?

    Check whether the following logic is correct:

    2. Why do the read receipts become invalid after the app is uninstalled and then reinstalled?

    In the one-to-one chat scenario, if the recipient calls markC2CMessageAsRead to mark a message as read, the read receipt received by the sender contains timestamp. Based on timestamp, the SDK determines whether the other party reads the message. Currently, timestamp is stored locally, and will be lost when the app is reinstalled.

    3. How is a message containing multiple Elem objects parsed?

    To reduce the message complexity, the SDK API 2.0 no longer supports creation of a message containing multiple Elem objects. If you receive a message containing multiple Elem objects from the API of an earlier version, perform the steps below:

    1. Parse the first Elem object as usual.
    2. Use the getNextElem method of the first Elem object to obtain the next Elem object. If the next Elem object exists, the Elem object instance is returned. Otherwise, null is returned.
    @Override
    public void onRecvNewMessage(V2TIMMessage msg) {
        // View the first `Elem` object.
        int elemType = msg.getElemType();
        if (elemType == V2TIMMessage.V2TIM_ELEM_TYPE_TEXT) {
            // Text message
            V2TIMTextElem v2TIMTextElem = msg.getTextElem();
            String text = v2TIMTextElem.getText();
            // Check whether `v2TIMTextElem` is followed by more `Elem` objects.
            V2TIMElem elem = v2TIMTextElem.getNextElem();
            while (elem != null) {
                // Identify the Elem type. Here, `V2TIMCustomElem` is used as an example.
                if (elem instanceof V2TIMCustomElem) {
                    V2TIMCustomElem customElem = (V2TIMCustomElem) elem;
                    byte[] data = customElem.getData();
                }
                // Continue to check whether current `Elem` is followed by more `Elem` objects.
                elem = elem.getNextElem();
            }
            // If `elem` is `null`, all `Elem` objects have been parsed.
        }
    }

    4. How are different types of messages parsed?

    It is complex to parse a message. We provide the sample code for parsing different types of messages. You can copy the code to your project, and perform secondary development based on your actual needs.

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