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Subscribe & Receive Message

After we have connected to broker, we can subscribe to any topic that we want and receive emitted message from that particular topic when the broker pushes the message.

Subscribe to Topic​

To subscribe to a topic from the broker, invoke susbscribe method on CourierClient passing the topic string and QoS.

courierClient.subscribe("chat/user1", QoS.one);

Received Message from Subscribed Topic​

After you have subscribed to the topic, you need to listen to a message stream passing the associated topic. courierMessageStream will loop message adapters trying to decode the data into specified type, the first one that is able to decode, will be used. You will need pass a decoder parameter to return instance of your object given 1 dynamic parameter depending on the adapter (JSONMessageAdapter pass you Map<String, dynamic>, BytesMessageAdapter pass you Uint8List)

Optionally you can pass MessageAdapter If this is passed, it will use it decode the data to `T`` type, otherwise it will use the messageAdapters list passed when initializing CourierClient.

/// This uses BytesMessageAdapter passed when initializing CourierClient and constructor tear-offs TestData.fromBytes
courierClient
    .courierMessageStream<TestData>(
        "orders/6b57d4e5-0fce-4917-b343-c8a1c77405e5/update",
        decoder: TestData.fromBytes)
    .listen((event) {
  print("Message received testData: ${event.textMessage}");
});

/// This uses passed JSONMessageAdapter and constructor tear-offs Person.fromJson
courierClient
    .courierMessageStream<Person>(
        "person/6b57d4e5-0fce-4917-b343-c8a1c77405e5/update",
        decoder: Person.fromJson,
        adapter: const JSONMessageAdapter())
    .listen((person) {
  print("Message received person: ${person.name}");

Receive Bytes(Uint8List) from Subscribed Topic​

After you have subscribed to the topic, you need to listen to a message stream passing the associated topic. The type of the parameter in the courierBytesStream listen callback is byte array UInt8List.

courierClient.courierBytesStream("chat/user1").listen((message) {
    print("Message received: ${event}");
});

Unsubscribe from Topic​

To unsubscribe from a topic, simply invoke unsubscribe passing the topic string.

courierClient.unsubscribe("chat/user/1");