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

/// A named channel for communicating with platform plugins using asynchronous
/// message passing.
///
/// Messages are encoded into binary before being sent, and binary messages
/// received are decoded into Dart values. The [MessageCodec] used must be
/// compatible with the one used by the platform plugin. This can be achieved
/// by creating a basic message channel counterpart of this channel on the
/// platform side. The Dart type of messages sent and received is [T],
/// but only the values supported by the specified [MessageCodec] can be used.
/// The use of unsupported values should be considered programming errors, and
/// will result in exceptions being thrown. The null message is supported
/// for all codecs.
///
/// The logical identity of the channel is given by its name. Identically named
/// channels will interfere with each other's communication.
///
/// See: <https://flutter.dev/platform-channels/>
class BasicMessageChannel<T> {
}

  /// Creates a [BasicMessageChannel] with the specified [name], [codec] and [binaryMessenger].
  ///
  /// The [name] and [codec] arguments cannot be null. The default [ServicesBinding.defaultBinaryMessenger]
  /// instance is used if [binaryMessenger] is null.
  const BasicMessageChannel(this.name, this.codec, { BinaryMessenger? binaryMessenger })
  
  /// The logical channel on which communication happens, not null.
  final String name;

  /// The message codec used by this channel, not null.
  final MessageCodec<T> codec;

  /// Sets a callback for receiving messages from the platform plugins on this
  /// channel. Messages may be null.
  ///
  /// The given callback will replace the currently registered callback for this
  /// channel, if any. To remove the handler, pass null as the `handler`
  /// argument.
  ///
  /// The handler's return value is sent back to the platform plugins as a
  /// message reply. It may be null.
  void setMessageHandler(Future<T> Function(T? message)? handler) {
    if (handler == null) {
      binaryMessenger.setMessageHandler(name, null);
    } else {
      binaryMessenger.setMessageHandler(name, (ByteData? message) async {
        return codec.encodeMessage(await handler(codec.decodeMessage(message)));
      });
    }
  }

  /// Sends the specified [message] to the platform plugins on this channel.
  ///
  /// Returns a [Future] which completes to the received response, which may
  /// be null.
  Future<T?> send(T message) async {
    return codec.decodeMessage(await binaryMessenger.send(name, codec.encodeMessage(message)));
  }

import 'package:flutter/services.dart';

static const BasicMessageChannel _basicMessageChannel =
  	const BasicMessageChannel('BasicMessageChannel', StringCodec());

/// 接收 Native 消息 , 并进行回复
/// 从 BasicMessageChannel 通道获取消息
_basicMessageChannel.setMessageHandler((message) => Future<String>((){
  setState(() {
    showMessage = "BasicMessageChannel : $message";
  });
  return "BasicMessageChannel : $message";
}));

	/// 向 Native 发送消息
    try {
       String response = await _basicMessageChannel.send(value);
    } on PlatformException catch (e) {
      print(e);
    }