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

public final class BasicMessageChannel<T> {

  @NonNull private final BinaryMessenger messenger;
  @NonNull private final String name;
  @NonNull private final MessageCodec<T> codec;

  /**
   * Creates a new channel associated with the specified {@link BinaryMessenger} and with the
   * specified name and {@link MessageCodec}.
   *
   * @param messenger a {@link BinaryMessenger}.
   * @param name a channel name String.
   * @param codec a {@link MessageCodec}.
   */
  public BasicMessageChannel(
      @NonNull BinaryMessenger messenger, @NonNull String name, @NonNull MessageCodec<T> 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 message handler on this channel for receiving messages sent from the Flutter
   * application.
   *
   * <p>Overrides any existing handler registration for (the name of) this channel.
   *
   * <p>If no handler has been registered, any incoming message on this channel will be handled
   * silently by sending a null reply.
   *
   * @param handler a {@link MessageHandler}, or null to deregister.
   */
  @UiThread
  public void setMessageHandler(@Nullable final MessageHandler<T> handler) {
    messenger.setMessageHandler(name, handler == null ? null : new IncomingMessageHandler(handler));
  }

  /** A handler of incoming messages. */
  public interface MessageHandler<T> {

    /**
     * Handles the specified message received from Flutter.
     *
     * <p>Handler implementations must reply to all incoming messages, by submitting a single reply
     * message to the given {@link Reply}. Failure to do so will result in lingering Flutter reply
     * handlers. The reply may be submitted asynchronously.
     *
     * <p>Any uncaught exception thrown by this method, or the preceding message decoding, will be
     * caught by the channel implementation and logged, and a null reply message will be sent back
     * to Flutter.
     *
     * <p>Any uncaught exception thrown during encoding a reply message submitted to the {@link
     * Reply} is treated similarly: the exception is logged, and a null reply is sent to Flutter.
     *
     * @param message the message, possibly null.
     * @param reply a {@link Reply} for sending a single message reply back to Flutter.
     */
    void onMessage(@Nullable T message, @NonNull Reply<T> reply);
  }

public final class BasicMessageChannel<T> {
  /**
   * Sends the specified message to the Flutter application on this channel.
   *
   * @param message the message, possibly null.
   */
  public void send(@Nullable T message) {
    send(message, null);
  }

  /**
   * Sends the specified message to the Flutter application, optionally expecting a reply.
   *
   * <p>Any uncaught exception thrown by the reply callback will be caught and logged.
   *
   * @param message the message, possibly null.
   * @param callback a {@link Reply} callback, possibly null.
   */
  @UiThread
  public void send(@Nullable T message, @Nullable final Reply<T> callback) {
    messenger.send(
        name,
        codec.encodeMessage(message),
        callback == null ? null : new IncomingReplyHandler(callback));
  }
}

FlutterFragment mFlutterFragment = FlutterFragment.withNewEngine().
        initialRoute("嵌入 FlutterFragment").build();

mFlutterFragment.getFlutterEngine();

// 初始化
BasicMessageChannel mBasicMessageChannel = new BasicMessageChannel(
        mFlutterFragment.getFlutterEngine().getDartExecutor(),
        "BasicMessageChannel",
        StringCodec.INSTANCE);

// 设置消息接收监听
mBasicMessageChannel.setMessageHandler(new BasicMessageChannel.MessageHandler<String>() {
    @Override
    public void onMessage(@Nullable String message, @NonNull BasicMessageChannel.Reply reply) {
        show_message.setText("Dart 通过 BasicMessageChannel 通道向 Native 发送 " + message + " 信息");
    }
});

// 点击按钮发送消息 , 并设置 Reply 接收 Dart 返回的消息
findViewById(R.id.channel1).setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        mBasicMessageChannel.send(
                "Native 通过 BasicMessageChannel 通道发送消息 Hello !",
                new BasicMessageChannel.Reply() {
                    @Override
                    public void reply(@Nullable Object reply) {
                        show_message.setText("Native 通过 BasicMessageChannel 通道发送消息 Hello 后 , Dart 反馈的信息 ");
                    }
                }
        );
    }
});

- **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 ;**