Receive messages

Register a message handler

Register a MessageHandler to receive all incoming messages.

tip

1. Register the handler during the app lifecycle, before connecting.
2. You can register multiple handlers with different identifiers.
3. Remove the handler when it is no longer needed to avoid memory leaks.

Method

Dart

static void addMessageHandler(String identifier, MessageHandler handler)

Parameters

Parameter	Type	Description
identifier	String	A unique ID for this handler.
handler	MessageHandler	Handler with callback properties for each event type.

MessageReceivedEvent

Property	Type	Description
message	Message	The received message object.
left	int?	Remaining messages in the current compensation package. After connection, the server delivers missed messages in packages of up to 200.
offline	bool?	Whether the message is a missed message.
hasPackage	bool?	Whether undelivered message packages remain on the server.

Code example

Dart

NCEngine.addMessageHandler('msg-handler', MessageHandler(
  onMessageReceived: (event) {
    print('New message: ${event.message.messageId}');
  },
));

Remove the handler when it is no longer needed:

Dart

NCEngine.removeMessageHandler('msg-handler');

Notes

• When receiving missed messages, the server sends packages of up to 200 messages to the client.
• hasPackage indicates whether more packages remain. left indicates how many messages remain in the current package.
• All missed messages are received when hasPackage is false and left is 0.