Flutter 實例 - 從本地到Flutter通訊 - Event Channels

public class MainActivity extends FlutterActivity {
    public static final String STREAM = "com.yourcompany.eventchannelsample/stream"; 

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        new EventChannel(getFlutterView(), STREAM).setStreamHandler(
                new EventChannel.StreamHandler() {
                    @Override
                    public void onListen(Object args, final EventChannel.EventSink events) {
                        Log.w(TAG, "adding listener");
                    }

                    @Override
                    public void onCancel(Object args) {
                        Log.w(TAG, "cancelling listener");
                    }
                }
        );
    }
}
複製代碼

爲了保證例子大多數手機能夠運行，咱們選用RxJava庫，將時間間隔做爲事件發送出來。注意你能夠將任何的信息發送到Flutter應用。

public void onListen(Object args, EventChannel.EventSink events) {
    Log.w(TAG, "adding listener");
    timerSubscription = Observable
            .interval(0, 1, TimeUnit.SECONDS)
            .subscribe(
                    (Long timer) -> {
                        Log.w(TAG, "emitting timer event " + timer);
                        events.success(timer);// 發送事件
                    },
                    (Throwable error) -> {
                        Log.e(TAG, "error in emitting timer", error);
                        events.error("STREAM", "Error in processing observable", error.getMessage());
                    },
                    () -> Log.w(TAG, "closing the timer observable")
            );
}

@Override
public void onCancel(Object args) {
    Log.w(TAG, "cancelling listener");
    if (timerSubscription != null) {
        timerSubscription.dispose();
        timerSubscription = null;
    }
}
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Dart 接受信息

Dart內置支持Stream，EventChannel使用Stream的功能通知什麼時候本地代碼開始發送事件和中止發送事件。爲了從本地開始發送事件，只須要給platform channel流添加監聽器。

static const stream =
    const EventChannel('com.yourcompany.eventchannelsample/stream');

StreamSubscription _timerSubscription = null;

void _enableTimer() {
  if (_timerSubscription == null) {
    _timerSubscription = stream.receiveBroadcastStream().listen(_updateTimer); // 添加監聽
  }
}

void _disableTimer() {
  if (_timerSubscription != null) {
    _timerSubscription.cancel();
    _timerSubscription = null;
  }
}
複製代碼

爲了顯示從本地來的更新次數，_updateTimer()方法這是修改_timer狀態

void _updateTimer(timer) {
  debugPrint("Timer $timer");
  setState(() => _timer = timer);
}
複製代碼

下面的log展現了，添加監聽，事件發送，事件接受，以及取消channel。

W/eventchannelsample(32641): adding listener
W/eventchannelsample(32641): emitting timer event 0
I/flutter (32641): Timer 0
W/eventchannelsample(32641): emitting timer event 1
I/flutter (32641): Timer 1
W/eventchannelsample(32641): emitting timer event 2
I/flutter (32641): Timer 2
W/eventchannelsample(32641): emitting timer event 3
I/flutter (32641): Timer 3
W/eventchannelsample(32641): emitting timer event 4
I/flutter (32641): Timer 4
W/eventchannelsample(32641): emitting timer event 5
I/flutter (32641): Timer 5
W/eventchannelsample(32641): cancelling listener
W/eventchannelsample(32641): adding listener
W/eventchannelsample(32641): emitting timer event 0
I/flutter (32641): Timer 0
W/eventchannelsample(32641): emitting timer event 1
I/flutter (32641): Timer 1
複製代碼