Flutter-OpenHarmony Native Interaction (Part 2)

Harmony OS Next

Flutter-OpenHarmony Native Interaction (Part 2)

Flutter's Three Fundamental Channels

• MethodChannel: Primary method for calling native methods and receiving return values, suitable for one-time calls.
• EventChannel: For continuous communication via event/data streams, e.g., monitoring sensor data.
• BasicMessageChannel: Transmits strings or binary information, ideal for bidirectional communication and rapid transfer of simple data.

BasicMessageChannel (Bidirectional Channel)

1. Flutter Side Code

• Create BasicMessageChannel instance
• Send messages to platform and receive responses

// Create instance
final _basicChannel = const BasicMessageChannel(
      "flutter.ohos.example/base_test", StandardMessageCodec());

// Call method and receive response from platform
final String? reply = await _basicChannel.send('increment');

1. OpenHarmony Side Code

• Implement FlutterPlugin's onAttachedToEngine method
• Create matching BasicMessageChannel instance
• Handle messages in onMessage callback
• Reply with response data

export default class TestPlugin implements FlutterPlugin {

  private basicChannel?: BasicMessageChannel<Any>;
  private counter = 0;

  onAttachedToEngine(binding: FlutterPluginBinding): void {
    this.basicChannel = new BasicMessageChannel(
      binding.getBinaryMessenger(),
      "flutter.ohos.example/base_test", 
      new StandardMessageCodec()
    );

    this.basicChannel.setMessageHandler({
      onMessage(message: Any, reply: Reply<Any>) {
        Log.i(TAG, "Received message from Flutter. Current counter: $counter");
        // Process message from Flutter
        counter++;
        reply.reply("Counter value: $counter");
      }
    })
  }
}

EventChannel (Event Monitoring)

1. Flutter Side Code

• Create EventChannel instance
• Listen for event broadcasts

// Create instance
final _eventChannel = const EventChannel('flutter.ohos.example/event_test');

// Listen for event callbacks
_eventChannel.receiveBroadcastStream().listen((event) {
    print("EventChannel event: $event")
});

1. OpenHarmony Side Code

• Implement FlutterPlugin's onAttachedToEngine method
• Create matching EventChannel instance
• Set up eventSink for data streaming
• Use eventSink to send data to Flutter

export default class TestPlugin implements FlutterPlugin {

  private eventChannel?: EventChannel;
  private eventSink?: EventSink;

  onAttachedToEngine(binding: FlutterPluginBinding): void {
    this.eventChannel = new EventChannel(
      binding.getBinaryMessenger(), 
      "flutter.ohos.example/event_test"
    );

    this.eventChannel.setStreamHandler({
      onListen(args: Any, events: EventSink): void {
        that.eventSink = events;  // Store event sink
      },
      onCancel(args: Any): void {
        that.eventSink = undefined;  // Clear reference
      }
    });
  }
}

Sending Data to Flutter

// ...
// Using eventSink sends data to Flutter's event listener
that.eventSink?.success("Event message from OHOS");