Messages that are started from a particular message are called Threaded messages or simply threads. Each Thread is attached to a message which is the Parent message for that thread.

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Send Message in a Thread

As mentioned in the Send a Message section, you can send a message to a User or a Group by mentioning the receiver (uid/guid) and receiverType(user/group). A message can be categorized as:
  1. Text Message
  2. Media Message
  3. Custom Message.
  4. Interactive Message
Any of the above messages can be sent in a thread. As a thread is identified with a parent message, the parentMessageId must be set for the message. This will indicate that the message to be sent has to be a part of the thread of the message with the specified parentMessageId. This can be achieved using the parentMessageId parameter provided by the object of the TextMessage, MediaMessage and CustomMessage class. The id specified in the parentMessageId parameter maps the message sent to the particular thread. Example to Send a Text Message in a thread in a user conversation. 
String receiverID = "UID";
String messagesText = "Hello";
String receiverType = CometChatConversationType.user;
String type = CometChatMessageType.text;

TextMessage textMessage = TextMessage(
                        text: messagesText,
                        receiverUid: receiverID,
                        receiverType: receiverType,
                        type: type);
textMessage.parentMessageId = 103

CometChat.sendMessage(textMessage,onSuccess: (TextMessage message) {
debugPrint("Message sent successfully:  $message");
}, onError: (CometChatException e) {
debugPrint("Message sending failed with exception:  ${e.message}");
});
The above snippet shows how a message with the text “Hello” can be sent in the thread with parentMessageId 103. Similarly, using the parentMessageId parameter, Media and Custom Messages can be sent in threads too.

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Receiving Real-Time Messages

The procedure to receive real-time messages is exactly the same as mentioned in the Receive Messages. This can be achieved using the MessageListener class provided by the SDK. To add a MessageListener, you can use the addMessageListener() method of the SDK. The only thing that needs to be checked is if the received message belongs to the active thread. This can be done using parentMessageId field of the message object. 
class Class_Name  with MessageListener {
	int activeParentMessageId= 103;
//CometChat.addMessageListener("listenerId", this);
	@override
void onTextMessageReceived(TextMessage textMessage) {
   if(textMessage.parentMessageId == activeParentMessageId){
      debugPrint("Text message received successfully: $textMessage");
  }

}

@override
void onMediaMessageReceived(MediaMessage mediaMessage) {
  if(mediaMessage.parentMessageId== activeParentMessageId){
  	debugPrint("Media message received successfully: $mediaMessage");
  }
}

@override
void onCustomMessageReceived(CustomMessage customMessage) {
  if(customMessage.parentMessageId== activeParentMessageId){
    debugPrint("Custom message received successfully: $customMessage");
  }
}
}

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Fetch all the messages for any particular thread.

You can fetch all the messages belonging to a particular thread by using the MessagesRequest class. The MessageRequestBuilder builds the MessageRequest object using the following functions:
  1. parentMessageId: Takes the parentId of the message as argument whose thread needs to be requested.
  2. build(): returns the MessageRequest object.
Once you have the MessagesRequest object, you can call the fetchPrevious() method to get the latest messages in the thread. In one iteration, a maximum of 100 messages can be fetched. If you wish to fetch the next set of messages, you need to call the fetchPrevious() method again on the same object. 
String UID = "cometchat-uid-1";

MessagesRequest messageRequest = (MessagesRequestBuilder()
          ..uid = UID
          ..parentMessageId = 103
          ..limit = 50).build();

messageRequest.fetchPrevious(onSuccess: (List<BaseMessage> list) {
         debugPrint("Message fetching Successful");
      }, onError: (CometChatException e) {
        debugPrint("Message fetching failed with exception: ${e.message}");
      });

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Avoid Threaded Messages in User/Group Conversations

While fetching messages for normal user/group conversations using the MessagesRequest, the threaded messages by default will be a part of the list of messages received. In order to exclude the threaded messages from the list of user/group messages, you need to use the hideReplies parameter of the MessagesRequestBuilder class. This method takes a boolean argument which when set to true excludes the messages belonging to threads from the list of messages. 
String UID = "cometchat-uid-1";

MessagesRequest messageRequest = (MessagesRequestBuilder()
          ..uid = UID
          ..hideReplies = true
          ..limit = 50).build();

messageRequest.fetchNext(onSuccess: (List<BaseMessage> list) {
         debugPrint("Message fetching Successful");
      }, onError: (CometChatException e) {
        debugPrint("Message fetching failed with exception: ${e.message}");
      });
The above snippet will return messages between the logged in user and cometchat-uid-1 excluding all the threaded messages belonging to the same conversation.