【Flutter】Flutter 混合开发 ( Flutter 与 Native 通信 | Android 端实现 EventChannel 通信 )

public final class EventChannel {
  private static final String TAG = "EventChannel#";

  private final BinaryMessenger messenger;
  private final String name;
  private final MethodCodec codec;

  /**
   * Creates a new channel associated with the specified {@link BinaryMessenger} and with the
   * specified name and the standard {@link MethodCodec}.
   *
   * @param messenger a {@link BinaryMessenger}.
   * @param name a channel name String.
   */
  public EventChannel(BinaryMessenger messenger, String name) {
    this(messenger, name, StandardMethodCodec.INSTANCE);
  }

  /**
   * Creates a new channel associated with the specified {@link BinaryMessenger} and with the
   * specified name and {@link MethodCodec}.
   *
   * @param messenger a {@link BinaryMessenger}.
   * @param name a channel name String.
   * @param codec a {@link MessageCodec}.
   */
  public EventChannel(BinaryMessenger messenger, String name, MethodCodec codec) {
    if (BuildConfig.DEBUG) {
      if (messenger == null) {
        Log.e(TAG, "Parameter messenger must not be null.");
      }
      if (name == null) {
        Log.e(TAG, "Parameter name must not be null.");
      }
      if (codec == null) {
        Log.e(TAG, "Parameter codec must not be null.");
      }
    }
    this.messenger = messenger;
    this.name = name;
    this.codec = codec;
  }
}

  /**
   * Registers a stream handler on this channel.
   *
   * <p>Overrides any existing handler registration for (the name of) this channel.
   *
   * <p>If no handler has been registered, any incoming stream setup requests will be handled
   * silently by providing an empty stream.
   *
   * @param handler a {@link StreamHandler}, or null to deregister.
   */
  @UiThread
  public void setStreamHandler(final StreamHandler handler) {
    messenger.setMessageHandler(
        name, handler == null ? null : new IncomingStreamRequestHandler(handler));
  }

  /**
   * Handler of stream setup and teardown requests.
   *
   * <p>Implementations must be prepared to accept sequences of alternating calls to {@link
   * #onListen(Object, EventSink)} and {@link #onCancel(Object)}. Implementations should ideally
   * consume no resources when the last such call is not {@code onListen}. In typical situations,
   * this means that the implementation should register itself with platform-specific event sources
   * {@code onListen} and deregister again {@code onCancel}.
   */
  public interface StreamHandler {
    /**
     * Handles a request to set up an event stream.
     *
     * <p>Any uncaught exception thrown by this method will be caught by the channel implementation
     * and logged. An error result message will be sent back to Flutter.
     *
     * @param arguments stream configuration arguments, possibly null.
     * @param events an {@link EventSink} for emitting events to the Flutter receiver.
     */
    void onListen(Object arguments, EventSink events);

    /**
     * Handles a request to tear down the most recently created event stream.
     *
     * <p>Any uncaught exception thrown by this method will be caught by the channel implementation
     * and logged. An error result message will be sent back to Flutter.
     *
     * <p>The channel implementation may call this method with null arguments to separate a pair of
     * two consecutive set up requests. Such request pairs may occur during Flutter hot restart. Any
     * uncaught exception thrown in this situation will be logged without notifying Flutter.
     *
     * @param arguments stream configuration arguments, possibly null.
     */
    void onCancel(Object arguments);
  }

  /**
   * Event callback. Supports dual use: Producers of events to be sent to Flutter act as clients of
   * this interface for sending events. Consumers of events sent from Flutter implement this
   * interface for handling received events (the latter facility has not been implemented yet).
   */
  public interface EventSink {
    /**
     * Consumes a successful event.
     *
     * @param event the event, possibly null.
     */
    void success(Object event);

    /**
     * Consumes an error event.
     *
     * @param errorCode an error code String.
     * @param errorMessage a human-readable error message String, possibly null.
     * @param errorDetails error details, possibly null
     */
    void error(String errorCode, String errorMessage, Object errorDetails);

    /**
     * Consumes end of stream. Ensuing calls to {@link #success(Object)} or {@link #error(String,
     * String, Object)}, if any, are ignored.
     */
    void endOfStream();
  }

// 初始化 EventChannel 实例对象
EventChannel mEventChannel = new EventChannel(
        mFlutterFragment.getFlutterEngine().getDartExecutor(),
        "EventChannel");

mEventChannel.setStreamHandler(new EventChannel.StreamHandler() {
    /**
     * 事件流建立成功会回调该方法
     * @param arguments
     * @param events
     */
    @Override
    public void onListen(Object arguments, EventChannel.EventSink events) {
        mEventSink = events;
        Log.i(TAG, "事件流建立成功");
    }
    
    @Override
    public void onCancel(Object arguments) {
        mEventSink = null;
    }
});

findViewById(R.id.channel2).setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Log.i(TAG, "Native 通过 EventChannel 通道发送消息 , mEventSink : " + mEventSink);
        // 点击按钮 , 向 Flutter 端发送数据
        if (mEventSink != null) {
            mEventSink.success("Native 通过 EventChannel 通道发送消息 Hello !");
        }
    }
});

// 初始化 EventChannel 实例对象
mEventChannel = new EventChannel(
        mFlutterFragment.getFlutterEngine().getDartExecutor(),
        "EventChannel");

mEventChannel.setStreamHandler(new EventChannel.StreamHandler() {
    /**
     * 事件流建立成功会回调该方法
     * @param arguments
     * @param events
     */
    @Override
    public void onListen(Object arguments, EventChannel.EventSink events) {
        mEventSink = events;
        Log.i(TAG, "事件流建立成功");
    }
    @Override
    public void onCancel(Object arguments) {
        mEventSink = null;
    }
});

// 注册 EventChannel 监听
_streamSubscription = _eventChannel
    .receiveBroadcastStream()
/// StreamSubscription<T> listen(void onData(T event)?,
///   {Function? onError, void onDone()?, bool? cancelOnError});
    .listen(
  /// EventChannel 接收到 Native 信息后 , 回调的方法
        (message) {
      print("Flutter _eventChannel listen 回调");
      setState(() {
        /// 接收到消息 , 显示在界面中
        showMessage = message;
      });
    },
    onError: (error){
      print("Flutter _eventChannel listen 出错");
      print(error);
    }
);

/**
 * 事件流建立成功会回调该方法
 * @param arguments
 * @param events
 */
@Override
public void onListen(Object arguments, EventChannel.EventSink events) {
    mEventSink = events;
    Log.i(TAG, "事件流建立成功");
}

// 点击按钮 , 向 Flutter 端发送数据
if (mEventSink != null) {
    mEventSink.success("Native 通过 EventChannel 通道发送消息 Hello !");
}

(message) {
  print("Flutter _eventChannel listen 回调");
  setState(() {
    /// 接收到消息 , 显示在界面中
    showMessage = message;
  });

- **Flutter Module 工程 :** [https://github.com/han1202012/flutter\_module](https://github.com/han1202012/flutter_module)
- **Android 应用 :** [https://github.com/han1202012/flutter\_native](https://github.com/han1202012/flutter_native)
- **注意 : 上面两个工程要放在同一个目录中 , 否则编译不通过 ;**