Flutter 与 Android原生 相互通信：BasicMessageChannel、MethodChannel、EventChannel

前言

本文主要讲解，使用不同的 Channel 让 Flutter 和 Android原生 进行通信，由于只是讲解两端通信，所以可视化效果不好；

不过我写了一篇专门讲解 Flutter 嵌入 Android原生View的文章

Flutter 页面嵌入 Android原生 View-CSDN博客

可以先看完，再结合案例自己改动一下，做到可视化，不过我还是建议优先看当前文章。

我采用在Android原生延时发送方式，来模拟Android原生向Flutter 发送消息。

1、BasicMessageChannel

主要应用于传输数据的通道，目前提供了以下几种消息类型：

JSONMessageCodec、StandardMessageCodec、StringCodec、BinaryCodec；

默认使用的消息类型是 StandardMessageCodec。

下面图片是 Flutter和Android原生，分别支持的数据类型 和 对应关系；

1.1 JSONMessageCodec

Json字符串。

1.2 StandardMessageCodec

标准类型，可以看作默认类型，支持的类型也是最多的。

1.3 StringCodec

字符串。

1.4 BinaryCodec

二进制，比如传输文件。

我挑了两个最常用的类型进行演示，比如Flutter向Android原生发送请求，Android原生收到请求后将数据响应给Flutter；

BasicMessageChannel的监听回调，没有提供具体调用了哪个函数的标识，所以在演示PUT时，我会先将GET相关代码注释，反之也一样；

如果和其他Channel配合使用可以解决这个注释问题， 比如BasicMessageChannel 和 MethodChannel 一起使用，这个案例我放在最后讲解，这一阶段先麻烦一下；

传输 BinaryCodec，我使用的是音频文件，传输完成默认开始播放，友情提示，戴耳机或者声音小点，避免社S。

在Flutter添加音频播放库，库的具体地址

just_audio | Flutter Package

just_audio: ^0.9.36

Android原生 需要的配置，app/build.gradle

defaultConfig {
     ... ...
    multiDexEnabled true
}

dependencies {
    def exoplayer_version = "2.18.5"
    implementation "com.google.android.exoplayer:exoplayer-core:$exoplayer_version"
    implementation "com.google.android.exoplayer:exoplayer-dash:$exoplayer_version"
    implementation "com.google.android.exoplayer:exoplayer-hls:$exoplayer_version"
    implementation "com.google.android.exoplayer:exoplayer-smoothstreaming:$exoplayer_version"

    implementation 'androidx.multidex:multidex:2.0.1'
}

传输JSONMessageCodec：

传输BinaryCodec

1.5 传输JSONMessageCodec

Flutter：main_json_basic_message_channel.dart

import 'dart:math';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

/// BasicMessageChannel
/// 使用Map类型，对应 Android端的 JSONObject类型
class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State createState() => _MyHomePageState();
}

class _MyHomePageState extends State {
  late BasicMessageChannel channel;

  // Android原生View 在Flutter引擎上注册的唯一标识，在Flutter端使用时必须一样
  static const String CHANNEL_NAME = 'flutter.mix.android/json_basic_message_channel';

  String msgState = "默认"; // 消息传递状态

  @override
  initState() {
    super.initState();
    initChannel();
  }

  /// 初始化消息通道
  initChannel() {
    channel = const BasicMessageChannel(CHANNEL_NAME,JSONMessageCodec()); // 创建 Flutter端和Android端的，相互通信的通道

    // 监听来自 Android端 的消息通道
    // Android端调用了函数，这个handler函数就会被触发
    channel.setMessageHandler(handler);
  }

  /// 监听来自 Android端 的消息通道
  /// Android端调用了函数，这个handler函数就会被触发
  Future handler(dynamic message) async {
    // PUT
    var androidCount = message['androidNum'];
    msgState = 'Flutter端接收Android端PUT请求成功，数据：$androidCount';
    setState(() {});
    return 0; // 返回给Android端

    // GET，这里模拟在Android端显示
    // var randomV = getRandomV();
    // Map map = {'flutterNum': randomV};
    // msgState = 'Flutter端接收Android端GET请求成功：$randomV';
    // setState(() {});
    // return map; // 返回给Android端
  }

  /// Flutter端 向 Android端 发送数据，PUT 操作
  flutterSendAndroidData() {
    var randomV = getRandomV();
    Map map = {'flutterNum': randomV};

    // Android端调用Reply相关回调函数后，then、catchError 会接收到

    channel.send(map).then((value) {
      var flutterNum = value['flutterNum'];
      msgState = 'Android端接收Flutter端PUT请求成功，数据：$flutterNum ----> 5秒后，Android端会向Flutter端发送PUT请求';
      setState(() {});
    }).catchError((e) {
      if (e is MissingPluginException) {
        debugPrint('flutterSendAndroidDataNotice --- Error：notImplemented --- 未找到Android端具体实现函数');
      } else {
        debugPrint('flutterSendAndroidDataNotice --- Error：$e');
      }
    });

  }

  ///  Flutter端 获取 Android端 数据，GET 操作
  flutterGetAndroidData() {

    // Android端调用Reply相关回调函数后，then、catchError 会接收到

    channel.send(null).then((value) {
      var androidCount = value['androidNum'];
      msgState = 'Android端接收Flutter端GET请求成功，数据：$androidCount ----> 5秒后，Android端会向Flutter端发送GET请求';
      setState(() {});
    }).catchError((e) {
      if (e is MissingPluginException) {
        debugPrint('flutterGetAndroidDataNotice --- Error：notImplemented --- 未找到Android端具体实现函数');
      } else {
        debugPrint('flutterGetAndroidDataNotice --- Error：$e');
      }
    });
  }

  /// 获取随机数
  int getRandomV() {
    return Random().nextInt(100); // 随机数范围(0-99)
  }

  @override
  Widget build(BuildContext context) {
    const defaultStyle = TextStyle(
      fontSize: 16,
      color: Colors.orangeAccent,
      fontWeight: FontWeight.bold,
    );
    return Scaffold(
        backgroundColor: Colors.blueGrey,
        body: SafeArea(
          top: true,
          child: SizedBox(
            width: MediaQuery.of(context).size.width,
            height: MediaQuery.of(context).size.height,
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [
                SizedBox(
                    width: 300,
                    child: Text(
                        msgState,
                        textAlign: TextAlign.center,
                        style: defaultStyle)
                ),
                Padding(
                  padding: const EdgeInsets.symmetric(vertical: 16),
                  child: ElevatedButton(
                    onPressed: flutterSendAndroidData,
                    child: const Text('Flutter端向Android端发送数据'),
                  ),
                ),
                ElevatedButton(
                  onPressed: flutterGetAndroidData,
                  child: const Text('Flutter端获取Android端数据'),
                ),
              ],
            ),
          ),
        ));
  }

}

Android原生：TestJsonBasicMessageChannel.kt

package com.example.flutter_android_channel.channel

import android.os.Handler
import android.os.Looper
import android.util.Log
import io.flutter.plugin.common.BasicMessageChannel
import io.flutter.plugin.common.BinaryCodec
import io.flutter.plugin.common.BinaryMessenger
import io.flutter.plugin.common.JSONMessageCodec
import io.flutter.plugin.common.MethodChannel
import io.flutter.plugin.common.StandardMessageCodec
import io.flutter.plugin.common.StringCodec
import org.json.JSONException
import org.json.JSONObject

/**
 * BasicMessageChannel
 *
 * 使用 JSONObject类型，对应 Flutter端的 Map类型
 */
class TestJsonBasicMessageChannel(messenger: BinaryMessenger) :
    BasicMessageChannel.MessageHandler {

    private lateinit var mChannel: BasicMessageChannel

    companion object {
        // Android原生View 在Flutter引擎上注册的唯一标识，在Flutter端使用时必须一样
        private const val CHANNEL_NAME = "flutter.mix.android/json_basic_message_channel"
    }

    init {
        initChannel(messenger)
    }

    /**
     * 初始化消息通道
     */
    private fun initChannel(messenger: BinaryMessenger) {
        // 创建 Android端和Flutter端的，相互通信的通道
        // 通道名称，两端必须一致
        mChannel = BasicMessageChannel(messenger, CHANNEL_NAME, JSONMessageCodec.INSTANCE)

        // 监听来自 Flutter端 的消息通道
        // Flutter端调用了函数，这个handler函数就会被触发
        mChannel.setMessageHandler(this)
    }

    // ========================== PUT 操作 ==========================

    /**
     * 监听来自 Flutter端 的消息通道
     *
     * message： Android端 接收到 Flutter端 发来的 数据对象
     * reply：Android端 给 Flutter端 执行回调的接口对象
     */
    override fun onMessage(message: Any?, reply: BasicMessageChannel.Reply) {
        // 回调结果对象
        // 获取Flutter端传过来的数据
        val flutterCount = getMap(message.toString())?.get("flutterNum")
        Log.d("TAG", "flutterCount：$flutterCount")

        // 回调状态接口对象，里面只有一个回调方法
        // reply.reply(@Nullable T reply)
        reply.reply(message) // 返回给Flutter端

        Handler(Looper.getMainLooper()).postDelayed({
            androidSendFlutterData()
        }, 5000)
    }

    /**
     * Android端 向 Flutter端 发送数据
     */
    private fun androidSendFlutterData() {
        val map: MutableMap = mutableMapOf()
        map["androidNum"] = getRandomV() // 随机数范围(0-99)

        mChannel.send(map, object : BasicMessageChannel.Reply {

            override fun reply(reply: Any?) {
                // 获取Flutter端传过来的数据
                Log.d("TAG", "reply：$reply")
            }

        })
    }

    // ========================== GET 操作 ==========================

//    /**
//     * 监听来自 Flutter端 的消息通道
//     *
//     * message： Android端 接收到 Flutter端 发来的 数据对象
//     * reply：Android端 给 Flutter端 执行回调的接口对象
//     */
//    override fun onMessage(message: Any?, reply: BasicMessageChannel.Reply) {
//        val map: MutableMap = mutableMapOf()
//        map["androidNum"] = getRandomV() // 随机数范围(0-99)
//        reply.reply(map) // 返回给Flutter端
//
//        Handler(Looper.getMainLooper()).postDelayed({
//            androidGetFlutterData()
//        }, 5000)
//    }
//
//    /**
//     * Android端 获取 Flutter端 数据
//     */
//    private fun androidGetFlutterData() {
//        mChannel.send(null, object : BasicMessageChannel.Reply {
//
//            override fun reply(reply: Any?) {
//                // 获取Flutter端传过来的数据
//                val flutterCount = getMap(reply.toString())?.get("flutterNum")
//                Log.d("TAG", "flutterCount：$flutterCount")
//            }
//
//        })
//    }

    /**
     * 获取随机数
     */
    private fun getRandomV() = (0..100).random()

    /**
     * 解除绑定
     */
    fun closeChannel() {
        mChannel.setMessageHandler(null)
    }

    /**
     * Json 转 Map
     */
    private fun getMap(jsonString: String?): HashMap? {
        val jsonObject: JSONObject
        try {
            jsonObject = JSONObject(jsonString)
            val keyIter: Iterator = jsonObject.keys()
            var key: String
            var value: Any
            var valueMap = HashMap()
            while (keyIter.hasNext()) {
                key = keyIter.next()
                value = jsonObject[key] as Any
                valueMap[key] = value
            }
            return valueMap
        } catch (e: JSONException) {
            e.printStackTrace()
        }
        return null
    }
}

Android原生：MainActivity.kt

package com.example.flutter_android_channel

import com.example.flutter_android_channel.channel.TestJsonBasicMessageChannel
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine

class MainActivity : FlutterActivity() {

    private lateinit var testJsonBasicMessageChannel: TestJsonBasicMessageChannel

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        testJsonBasicMessageChannel = TestJsonBasicMessageChannel(flutterEngine.dartExecutor.binaryMessenger)
    }

    override fun onDestroy() {
        super.onDestroy()
        testJsonBasicMessageChannel.closeChannel()
    }

}

1.6 传输BinaryCodec

Flutter：main_byte_basic_message_channel.dart

import 'package:just_audio/just_audio.dart';
import 'dart:typed_data';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

/// BasicMessageChannel
/// 使用ByteData类型，对应 Android端的 ByteBuffer类型
class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State createState() => _MyHomePageState();
}

class _MyHomePageState extends State {
  late BasicMessageChannel channel;

  // Android原生View 在Flutter引擎上注册的唯一标识，在Flutter端使用时必须一样
  static const String CHANNEL_NAME = 'flutter.mix.android/byte_basic_message_channel';

  String msgState = "默认"; // 消息传递状态

  @override
  initState() {
    super.initState();
    initChannel();
  }

  /// 初始化消息通道
  initChannel() {
    channel = const BasicMessageChannel(CHANNEL_NAME,BinaryCodec()); // 创建 Flutter端和Android端的，相互通信的通道

    // 监听来自 Android端 的消息通道
    // Android端调用了函数，这个handler函数就会被触发
    channel.setMessageHandler(handler);
  }

  /// 监听来自 Android端 的消息通道
  /// Android端调用了函数，这个handler函数就会被触发
  Future handler(dynamic message) async {
    // PUT
    var data = message as ByteData;
    loadMusic(data);
    msgState = 'Flutter端接收Android端PUT请求成功，音频加载完毕，开始播放';
    setState(() {});
    return ByteData.view(Uint8List(0).buffer); // 返回给Android端

    // GET，这里模拟在Android端播放音乐
    // final data = await rootBundle.load('assets/music/di_jia_a.mp3');
    // loadMusic(data);
    // msgState = 'Flutter端接收Android端GET请求成功，音频加载完毕，开始播放';
    // setState(() {});
    // return data; // 返回给Android端
  }

  /// Flutter端 向 Android端 发送数据，PUT 操作
  flutterSendAndroidData() async {
    final byteData = await rootBundle.load('assets/music/di_jia_a.mp3');

    // Android端调用Reply相关回调函数后，then、catchError 会接收到

    channel.send(byteData).then((value) {
      loadMusic(value);
      msgState = 'Android端接收Flutter端PUT请求成功，音频加载完毕，开始播放 --- 5秒钟后 Android端会向Flutter端发送PUT请求';
      setState(() {});
    }).catchError((e) {
      if (e is MissingPluginException) {
        debugPrint('flutterSendAndroidDataNotice --- Error：notImplemented --- 未找到Android端具体实现函数');
      } else {
        debugPrint('flutterSendAndroidDataNotice --- Error：$e');
      }
    });
  }

  ///  Flutter端 获取 Android端 数据，GET 操作
  flutterGetAndroidData() {

    // Android端调用Reply相关回调函数后，then、catchError 会接收到

    channel.send(null).then((value) {
      loadMusic(value);
      msgState = 'Android端接收Flutter端GET请求成功，音频加载完毕，开始播放 --- 5秒钟后 Android端会向Flutter端发送GET请求';
      setState(() {});
    }).catchError((e) {
      if (e is MissingPluginException) {
        debugPrint('flutterGetAndroidDataNotice --- Error：notImplemented --- 未找到Android端具体实现函数');
      } else {
        debugPrint('flutterGetAndroidDataNotice --- Error：$e');
      }
    });

  }

  final player = AudioPlayer();

  /// 加载音频
  loadMusic(ByteData data) async {
    var buffer = data.buffer;
    var uint8list = buffer.asUint8List(data.offsetInBytes,data.lengthInBytes);
    var audioSource = AudioSource.uri(Uri.dataFromBytes(uint8list));
    await player.setAudioSource(audioSource);
    player.play(); // 播放音乐
  }

  /// 播放或暂停
  palsyOrPause() {
    if(player.playing) {
      player.pause();
    }
  }

  @override
  Widget build(BuildContext context) {
    const defaultStyle = TextStyle(
      fontSize: 16,
      color: Colors.orangeAccent,
      fontWeight: FontWeight.bold,
    );
    return Scaffold(
        backgroundColor: Colors.blueGrey,
        body: SafeArea(
          top: true,
          child: SizedBox(
            width: MediaQuery.of(context).size.width,
            height: MediaQuery.of(context).size.height,
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [
                SizedBox(
                    width: 300,
                    child: Text(
                        msgState,
                        textAlign: TextAlign.center,
                        style: defaultStyle)
                ),
                Padding(
                  padding: const EdgeInsets.symmetric(vertical: 16),
                  child: ElevatedButton(
                    onPressed: flutterSendAndroidData,
                    child: const Text('Flutter端向Android端发送数据'),
                  ),
                ),
                Padding(
                  padding: const EdgeInsets.only(bottom: 16),
                  child: ElevatedButton(
                    onPressed: flutterGetAndroidData,
                    child: const Text('Flutter端获取Android端数据'),
                  ),
                ),
                ElevatedButton(
                  onPressed: palsyOrPause,
                  child: Text('暂停'),
                ),
              ],
            ),
          ),
        ));
  }

}

Android原生：TestByteBasicMessageChannel.kt

package com.example.flutter_android_channel.channel

import android.content.Context
import android.os.Handler
import android.os.Looper
import android.util.Log
import com.google.common.io.ByteStreams
import io.flutter.plugin.common.BasicMessageChannel
import io.flutter.plugin.common.BinaryCodec
import io.flutter.plugin.common.BinaryMessenger
import java.nio.ByteBuffer
import java.nio.ByteOrder

/**
 * BasicMessageChannel
 *
 * 使用 ByteBuffer类型，对应 Flutter端的 ByteData类型
 */
class TestByteBasicMessageChannel(messenger: BinaryMessenger, private val context: Context) :
    BasicMessageChannel.MessageHandler {

    private lateinit var mChannel: BasicMessageChannel

    companion object {
        // Android原生View 在Flutter引擎上注册的唯一标识，在Flutter端使用时必须一样
        private const val CHANNEL_NAME = "flutter.mix.android/byte_basic_message_channel"
    }

    init {
        initChannel(messenger)
    }

    /**
     * 初始化消息通道
     */
    private fun initChannel(messenger: BinaryMessenger) {
        // 创建 Android端和Flutter端的，相互通信的通道
        // 通道名称，两端必须一致
        mChannel = BasicMessageChannel(messenger, CHANNEL_NAME, BinaryCodec.INSTANCE)

        // 监听来自 Flutter端 的消息通道
        // Flutter端调用了函数，这个handler函数就会被触发
        mChannel.setMessageHandler(this)
    }

    // ========================== PUT 操作 ==========================

    /**
     * 监听来自 Flutter端 的消息通道
     *
     * byteBuffer： Android端 接收到 Flutter端 发来的 数据对象
     * reply：Android端 给 Flutter端 执行回调的接口对象
     */
    override fun onMessage(byteBuffer: ByteBuffer?, reply: BasicMessageChannel.Reply) {
        // 回调结果对象
        // 获取Flutter端传过来的数据
        Log.d("TAG", "byteBuffer：$byteBuffer")

        // 回调接口对象，里面只有一个回调方法
        // reply.reply(@Nullable T reply)
        byteBuffer?.order(ByteOrder.nativeOrder())
        val direct = ByteBuffer.allocateDirect(byteBuffer!!.capacity())
        direct.put(byteBuffer)
        reply.reply(direct) // 返回给Flutter端

        Handler(Looper.getMainLooper()).postDelayed({
            androidSendFlutterData()
        }, 5000)
    }

    /**
     * Android端 向 Flutter端 发送数据
     */
    private fun androidSendFlutterData() {
        // 读取assert目录下的音频文件
        val fileInputStream = context.assets.open("music/di_jia_b.mp3")
        val targetArray = ByteStreams.toByteArray(fileInputStream)
        val byteBuffer = ByteBuffer.wrap(targetArray)

        byteBuffer.order(ByteOrder.nativeOrder())
        val direct = ByteBuffer.allocateDirect(byteBuffer.capacity())
        direct.put(byteBuffer)

        mChannel.send(direct,object : BasicMessageChannel.Reply {

            override fun reply(reply: ByteBuffer?) {
                Log.d("TAG", "reply：$reply")
            }

        })
    }

    // ========================== GET 操作 ==========================

//    /**
//     * 监听来自 Flutter端 的消息通道
//     *
//     * byteBuffer： Android端 接收到 Flutter端 发来的 数据对象
//     * reply：Android端 给 Flutter端 执行回调的接口对象
//     */
//    override fun onMessage(byteBuffer: ByteBuffer?, reply: BasicMessageChannel.Reply) {
//        // 读取assert目录下的音频文件
//        val fileInputStream = context.assets.open("music/di_jia_b.mp3")
//        val targetArray = ByteStreams.toByteArray(fileInputStream)
//        val byteBuffer = ByteBuffer.wrap(targetArray)
//
//        byteBuffer.order(ByteOrder.nativeOrder())
//        val direct = ByteBuffer.allocateDirect(byteBuffer.capacity())
//        direct.put(byteBuffer)
//        reply.reply(direct) // 返回给Flutter端
//
//        Handler(Looper.getMainLooper()).postDelayed({
//            androidGetFlutterData()
//        }, 5000)
//    }
//
//    /**
//     * Android端 获取 Flutter端 数据
//     */
//    private fun androidGetFlutterData() {
//        mChannel.send(null,object : BasicMessageChannel.Reply {
//
//            override fun reply(reply: ByteBuffer?) {
//                // 获取Flutter端传过来的数据
//                Log.d("TAG", "reply：$reply")
//            }
//
//        })
//    }

    /**
     * 解除绑定
     */
    fun closeChannel() {
        mChannel.setMessageHandler(null)
    }

}

Android原生：MainActivity.kt

package com.example.flutter_android_channel

import com.example.flutter_android_channel.channel.TestByteBasicMessageChannel
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine

class MainActivity : FlutterActivity() {

    private lateinit var testByteBasicMessageChannel: TestByteBasicMessageChannel

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)        
        testByteBasicMessageChannel = TestByteBasicMessageChannel(flutterEngine.dartExecutor.binaryMessenger,this)        
    }

    override fun onDestroy() {
        super.onDestroy()
        testByteBasicMessageChannel.closeChannel()
    }

}

2、MethodChannel

主要应用于Flutter和Android原生之间函数相互调用，所以它提供methodName作为具体调用函数的标识，就不用像演示 BasicMessageChannel那样，需要注释代码。

默认使用的消息类型是 StandardMessageCodec。

Flutter：main_method_channel.dart

import 'dart:math';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

/// MethodChannel
class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State createState() => _MyHomePageState();
}

class _MyHomePageState extends State {
  late MethodChannel channel;

  // Android原生View 在Flutter引擎上注册的唯一标识，在Flutter端使用时必须一样
  static const String CHANNEL_NAME = 'flutter.mix.android/method_channel';
  static const String FLUTTER_SEND_ANDROID_DATA_NOTICE = 'flutterSendAndroidDataNotice'; // Flutter端 向 Android端 发送数据
  static const String FLUTTER_GET_ANDROID_DATA_NOTICE = 'flutterGetAndroidDataNotice'; // Flutter端 获取 Android端 数据
  static const String ANDROID_SEND_FLUTTER_DATA_NOTICE = 'androidSendFlutterDataNotice'; // Android端 向 Flutter端 发送数据
  static const String ANDROID_GET_FLUTTER_DATA_NOTICE = 'androidGetFlutterDataNotice'; // Android端 获取 Flutter端 数据

  String msgState = "默认"; // 消息传递状态

  @override
  initState() {
    super.initState();
    initChannel();
  }

  /// 初始化消息通道
  initChannel() {
    channel = const MethodChannel(CHANNEL_NAME); // 创建 Flutter端和Android端的，相互通信的通道

    // 监听来自 Android端 的消息通道
    // Android端调用了函数，这个handler函数就会被触发
    channel.setMethodCallHandler(handler);
  }

  /// 监听来自 Android端 的消息通道
  /// Android端调用了函数，这个handler函数就会被触发
  Future handler(MethodCall call) async {
    // 获取调用函数的名称
    final String methodName = call.method;
    switch (methodName) {
      case ANDROID_SEND_FLUTTER_DATA_NOTICE:
        {
          int androidCount = call.arguments['androidNum'];
          msgState = 'Flutter端接收Android端PUT请求成功，数据：$androidCount';
          setState(() {});

          return '$ANDROID_SEND_FLUTTER_DATA_NOTICE ---> success'; // 返回给Android端
        }
      case ANDROID_GET_FLUTTER_DATA_NOTICE:
      {
        msgState = 'Flutter端接收Android端GET请求成功，返回数据：${getRandomV()}';
        setState(() {});

        return '$ANDROID_GET_FLUTTER_DATA_NOTICE ---> success：${getRandomV()}'; // 返回给Android端
      }
      default:
        {
          return PlatformException(code: '-1', message: '未找到Flutter端具体实现函数', details: '具体描述'); // 返回给Android端
        }
    }
  }

  /// Flutter端 向 Android端 发送数据，PUT 操作
  flutterSendAndroidData() {
    var randomV = getRandomV();
    Map map = {'flutterNum': randomV};

    // Android端调用Result相关回调函数后，then、catchError 会接收到

    channel.invokeMethod(FLUTTER_SEND_ANDROID_DATA_NOTICE, map).then((value) {
      msgState = value;
      setState(() {});
    }).catchError((e) {
      if (e is MissingPluginException) {
        debugPrint('$FLUTTER_SEND_ANDROID_DATA_NOTICE --- Error：notImplemented --- 未找到Android端具体实现函数');
      } else {
        debugPrint('$FLUTTER_SEND_ANDROID_DATA_NOTICE --- Error：$e');
      }
    });

  }

  ///  Flutter端 获取 Android端 数据，GET 操作
  flutterGetAndroidData() {

    // Android端调用Result相关回调函数后，then、catchError 会接收到

    channel.invokeMethod(FLUTTER_GET_ANDROID_DATA_NOTICE).then((value) {
      msgState = value;
      setState(() {});
    }).catchError((e) {
      if (e is MissingPluginException) {
        debugPrint('$FLUTTER_GET_ANDROID_DATA_NOTICE --- Error：notImplemented --- 未找到Android端具体实现函数');
      } else {
        debugPrint('$FLUTTER_GET_ANDROID_DATA_NOTICE --- Error：$e');
      }
    });

  }

  /// 获取随机数
  int getRandomV() {
    return Random().nextInt(100); // 随机数范围(0-99)
  }

  @override
  Widget build(BuildContext context) {
    const defaultStyle = TextStyle(
        fontSize: 16,
        color: Colors.orangeAccent,
        fontWeight: FontWeight.bold,
    );
    return Scaffold(
        backgroundColor: Colors.blueGrey,
        body: SafeArea(
          top: true,
          child: SizedBox(
            width: MediaQuery.of(context).size.width,
            height: MediaQuery.of(context).size.height,
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [
                SizedBox(
                    width: 300,
                    child: Text(
                      msgState,
                      textAlign: TextAlign.center,
                      style: defaultStyle)
                ),
                Padding(
                  padding: const EdgeInsets.symmetric(vertical: 16),
                  child: ElevatedButton(
                    onPressed: flutterSendAndroidData,
                    child: const Text('Flutter端向Android端发送数据'),
                  ),
                ),
                ElevatedButton(
                  onPressed: flutterGetAndroidData,
                  child: const Text('Flutter端获取Android端数据'),
                ),
              ],
            ),
          ),
        ));
  }

}

Android原生：TestMethodChannel.kt

package com.example.flutter_android_channel.channel

import android.os.Handler
import android.os.Looper
import android.util.Log
import androidx.annotation.NonNull
import androidx.annotation.Nullable
import io.flutter.plugin.common.BinaryMessenger
import io.flutter.plugin.common.MethodCall
import io.flutter.plugin.common.MethodChannel
import kotlin.random.Random

/**
 * MethodChannel
 */
class TestMethodChannel(messenger: BinaryMessenger) : MethodChannel.MethodCallHandler {

    private lateinit var mChannel: MethodChannel

    companion object {
        // Android原生View 在Flutter引擎上注册的唯一标识，在Flutter端使用时必须一样
        private const val CHANNEL_NAME = "flutter.mix.android/method_channel"
        private const val ANDROID_SEND_FLUTTER_DATA_NOTICE: String = "androidSendFlutterDataNotice" // Android端 向 Flutter端 发送数据
        private const val ANDROID_GET_FLUTTER_DATA_NOTICE: String = "androidGetFlutterDataNotice" // Android端 获取 Flutter端 数据
        private const val FLUTTER_SEND_ANDROID_DATA_NOTICE: String = "flutterSendAndroidDataNotice" // Flutter端 向 Android端 发送数据
        private const val FLUTTER_GET_ANDROID_DATA_NOTICE: String = "flutterGetAndroidDataNotice" // Flutter端 获取 Android端 数据
    }

    init {
        initChannel(messenger)
    }

    /**
     * 初始化消息通道
     */
    private fun initChannel(messenger: BinaryMessenger) {
        // 创建 Android端和Flutter端的，相互通信的通道
        // 通道名称，两端必须一致
        mChannel = MethodChannel(messenger, CHANNEL_NAME)

        // 监听来自 Flutter端 的消息通道
        // Flutter端调用了函数，这个handler函数就会被触发
        mChannel.setMethodCallHandler(this)
    }

    /**
     * 监听来自 Flutter端 的消息通道
     *
     * call： Android端 接收到 Flutter端 发来的 数据对象
     * result：Android端 给 Flutter端 执行回调的接口对象
     */
    override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {
        // 获取调用函数的名称
        val methodName: String = call.method
        when (methodName) {
            FLUTTER_SEND_ANDROID_DATA_NOTICE -> {
                // 回调结果对象
                // 获取Flutter端传过来的数据
                val flutterCount: Int? = call.argument("flutterNum")
                result.success("Android端接收Flutter端PUT请求成功，数据：$flutterCount ----> 5秒后，Android端会向Flutter端发送PUT请求")

                Handler(Looper.getMainLooper()).postDelayed({
                    androidSendFlutterData()
                }, 5000)

                // 回调状态接口对象，里面有三个回调方法，都可以给Flutter端返回消息
                // result.success(result: Any?)
                // result.error(errorCode: String, errorMessage: String?, errorDetails: Any?)
                // result.notImplemented()
            }

            FLUTTER_GET_ANDROID_DATA_NOTICE -> {
                result.success("Android端接收Flutter端GET请求成功，返回数据：${getRandomV()} ----> 5秒后，Android端会向Flutter端发送GET请求")

                Handler(Looper.getMainLooper()).postDelayed({
                    androidGetFlutterData()
                }, 5000)
            }

            else -> {
                result.notImplemented()
            }
        }
    }

    /**
     * Android端 向 Flutter端 发送数据，相当于 PUT 操作
     */
    private fun androidSendFlutterData() {
        val map: MutableMap = mutableMapOf()
        map["androidNum"] = getRandomV() // 随机数范围(0-99)

        mChannel.invokeMethod(ANDROID_SEND_FLUTTER_DATA_NOTICE, map, object : MethodChannel.Result {
            override fun success(result: Any?) {
                Log.d("TAG", "$result")
            }

            override fun error(
                errorCode: String,
                errorMessage: String?,
                errorDetails: Any?
            ) {
                Log.d(
                    "TAG", "errorCode：$errorCode --- errorMessage：$errorMessage --- errorDetails：$errorDetails"
                )
            }

            /**
             * Flutter端 未实现 Android端 定义的接口方法
             */
            override fun notImplemented() {
                Log.d("TAG", "notImplemented")
            }
        })
    }

    /**
     * Android端 获取 Flutter端 数据，相当于 GET 操作
     */
    private fun androidGetFlutterData() {
        // 说一个坑，不传参数可以写null，
        // 但不能这样写，目前它没有这个重载方法，invokeMethod第二个参数是Object类型，所以编译器不会提示错误
        // mChannel.invokeMethod(ANDROID_GET_FLUTTER_DATA_NOTICE, object : MethodChannel.Result {

        // public void invokeMethod(@NonNull String method, @Nullable Object arguments)

        mChannel.invokeMethod(ANDROID_GET_FLUTTER_DATA_NOTICE, null, object : MethodChannel.Result {
            override fun success(result: Any?) {
                Log.d("TAG", "$result")
            }

            override fun error(
                errorCode: String,
                errorMessage: String?,
                errorDetails: Any?
            ) {
                Log.d(
                    "TAG", "errorCode：$errorCode --- errorMessage：$errorMessage --- errorDetails：$errorDetails"
                )
            }

            /**
             * Flutter端 未实现 Android端 定义的接口方法
             */
            override fun notImplemented() {
                Log.d("TAG", "notImplemented")
            }
        })
    }

    /**
     * 获取随机数
     */
    private fun getRandomV() = (0..100).random()

    /**
     * 解除绑定
     */
    fun closeChannel() {
        mChannel.setMethodCallHandler(null)
    }

}

Android原生：MainActivity.kt

package com.example.flutter_android_channel

import com.example.flutter_android_channel.channel.TestMethodChannel
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine

class MainActivity : FlutterActivity() {

TestByteBasicMessageChannel
    private lateinit var testMethodChannel: TestMethodChannel

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        testMethodChannel = TestMethodChannel(flutterEngine.dartExecutor.binaryMessenger)
    }

    override fun onDestroy() {
        super.onDestroy()
        testMethodChannel.closeChannel()
    }

}

3、EventChannel

主要应用于 原生端 向 Flutter 单向通信；

默认使用的消息类型是 StandardMessageCodec。

Flutter：main_single_event_channel.dart

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

/// EventChannel
/// 使用方式：单向通信
class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State createState() => _MyHomePageState();
}

class _MyHomePageState extends State {
  late EventChannel channel;

  // Android原生View 在Flutter引擎上注册的唯一标识，在Flutter端使用时必须一样
  static const String CHANNEL_NAME = 'flutter.mix.android/single_event_channel';

  StreamSubscription? streamSubscription;

  String msgState = "默认"; // 消息传递状态

  @override
  initState() {
    super.initState();
    initChannel();
  }

  /// 初始化消息通道
  initChannel() {
    channel = const EventChannel(CHANNEL_NAME); // 创建 Flutter端和Android端的，相互通信的通道

    // 监听来自 Android端 的消息通道
    // Android端调用了函数，这个handler函数就会被触发
    streamSubscription = channel
        .receiveBroadcastStream()
        .listen(onData, onError: onError, onDone: onDone);
  }

  /// 监听来自 Android端 的消息通道
  /// 这几个函数就会根据情况被触发

  /// 响应数据
  onData(dynamic data) {
    msgState = data;
    setState(() {});
  }

  /// 发生异常
  onError(dynamic error) {
    msgState = error;
    setState(() {});
  }

  /// 流被关闭
  onDone() {
    msgState = "流被关闭";
    setState(() {});
  }

  @override
  void dispose() {
    super.dispose();
    streamSubscription?.cancel();
  }

  @override
  Widget build(BuildContext context) {
    const defaultStyle = TextStyle(
      fontSize: 50,
      color: Colors.orangeAccent,
      fontWeight: FontWeight.bold,
    );
    return Scaffold(
        backgroundColor: Colors.blueGrey,
        body: SafeArea(
          top: true,
          child: SizedBox(
            width: MediaQuery.of(context).size.width,
            height: MediaQuery.of(context).size.height,
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [
                SizedBox(
                    width: 300,
                    child: Text(msgState,
                        textAlign: TextAlign.center, style: defaultStyle)),
              ],
            ),
          ),
        ));
  }
}

Android原生：TestSingleEventChannel.kt

package com.example.flutter_android_channel.channel

import android.os.CountDownTimer
import io.flutter.plugin.common.BinaryMessenger
import io.flutter.plugin.common.EventChannel

/**
 * EventChannel
 *
 * 使用方式：单向通信
 */
class TestSingleEventChannel(messenger: BinaryMessenger) : EventChannel.StreamHandler {

    private lateinit var mChannel: EventChannel

    companion object {
        // Android原生View 在Flutter引擎上注册的唯一标识，在Flutter端使用时必须一样
        private const val CHANNEL_NAME = "flutter.mix.android/single_event_channel"
    }

    init {
        initChannel(messenger)
    }

    /**
     * 初始化消息通道
     */
    private fun initChannel(messenger: BinaryMessenger) {
        // 创建 Android端和Flutter端的，相互通信的通道
        // 通道名称，两端必须一致
        mChannel = EventChannel(messenger, CHANNEL_NAME)

        // 监听来自 Flutter端 的消息通道
        // Flutter端调用了函数，这个handler函数就会被触发
        mChannel.setStreamHandler(this)
    }

    private var count: Int = 10

    override fun onListen(arguments: Any?, events: EventChannel.EventSink?) {

        // 一共10秒，每隔1秒执行一次
        object : CountDownTimer(10000, 1000) {
            override fun onTick(millisUntilFinished: Long) {
                // 还剩下多少秒，依次为2000、1000、0
                if (millisUntilFinished == 0L) {
                    cancel()
                }
                events?.success("${count--}")
            }

            override fun onFinish() { // 结束后的操作
                events?.success("${count--}")
            }
        }.start()

        // 给Flutter端返回消息
        // events?.endOfStream()
        // events?.success(event: Any?)
        // events?.error(errorCode: String?, errorMessage: String?, errorDetails: Any?)
        // events?.endOfStream() // 流结束
    }

    override fun onCancel(arguments: Any?) {

    }

    /**
     * 解除绑定
     */
    fun closeChannel() {
        mChannel.setStreamHandler(null)
    }

}

Android原生：MainActivity.kt

package com.example.flutter_android_channel

import com.example.flutter_android_channel.channel.TestSingleEventChannel
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine

class MainActivity : FlutterActivity() {

    private lateinit var testSingleEventChannel : TestSingleEventChannel

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        testSingleEventChannel = TestSingleEventChannel(flutterEngine.dartExecutor.binaryMessenger)
    }

    override fun onDestroy() {
        super.onDestroy()
        testSingleEventChannel.closeChannel()
    }

}

怀疑

• 它用到Stream，流在开发中，代表一连串数据，主要应用在传输文件，比如IO流；
• EventChannel.EventSink，它提供的那些函数名，一看就是返回操作，既然是返回，就需要前置条件，比如接收到请求；
• BinaryMessenger.send(String channel, ByteData? message)，我找到了方法，传输的数据类型是ByteData，结合前两项，逻辑通了，那是否意味着Flutter可以使用EventChannel主动向原生端发送请求？

1.0 撸起袖子，开始干

Flutter一切正常，成功发送数据，且Android原生也成功接收到数据，但遇到了解析异常；

17:53:44.737  E  Uncaught exception in binary message listener
                 java.lang.IllegalArgumentException: Message corrupted
                 	at io.flutter.plugin.common.StandardMessageCodec.readValueOfType(StandardMessageCodec.java:450)
                 	at io.flutter.plugin.common.StandardMessageCodec.readValue(StandardMessageCodec.java:340)
                 	at io.flutter.plugin.common.StandardMethodCodec.decodeMethodCall(StandardMethodCodec.java:48)
                 	at io.flutter.plugin.common.EventChannel$IncomingStreamRequestHandler.onMessage(EventChannel.java:195)
                 	at io.flutter.embedding.engine.dart.DartMessenger.invokeHandler(DartMessenger.java:295)
                 	at io.flutter.embedding.engine.dart.DartMessenger.lambda$dispatchMessageToQueue$0$io-flutter-embedding-engine-dart-DartMessenger(DartMessenger.java:322)
                 	at io.flutter.embedding.engine.dart.DartMessenger$$ExternalSyntheticLambda0.run(Unknown Source:12)
                 	at android.os.Handler.handleCallback(Handler.java:942)
                 	at android.os.Handler.dispatchMessage(Handler.java:99)
                 	at android.os.Looper.loopOnce(Looper.java:201)
                 	at android.os.Looper.loop(Looper.java:288)
                 	at android.app.ActivityThread.main(ActivityThread.java:7872)
                 	at java.lang.reflect.Method.invoke(Native Method)
                 	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
                 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:936)

1.1 异常分析

这个异常是在原生端触发的，默认使用的消息类型是 StandardMessageCodec，它的父类是MethodCodec抽象类，目前没有可以解析 ByteBuffer的子类，这就很矛盾，发送成功，接收成功，但不支持解析，于是我抱着侥幸的心态，跑去问官方，看看是不是我使用的方式不对。

StandardMessageCodec.java 中的数据解析方法；

 @Nullable
  protected Object readValueOfType(byte type, @NonNull ByteBuffer buffer) {
    final Object result;
    switch (type) {
      case NULL:
        result = null;
        break;
      case TRUE:
        result = true;
        break;
      case FALSE:
        result = false;
        break;
      case INT:
        result = buffer.getInt();
        break;
      case LONG:
        result = buffer.getLong();
        break;
      case BIGINT:
        {
          final byte[] hex = readBytes(buffer);
          result = new BigInteger(new String(hex, UTF8), 16);
          break;
        }
      case DOUBLE:
        readAlignment(buffer, 8);
        result = buffer.getDouble();
        break;
      case STRING:
        {
          final byte[] bytes = readBytes(buffer);
          result = new String(bytes, UTF8);
          break;
        }
      case BYTE_ARRAY:
        {
          result = readBytes(buffer);
          break;
        }
      case INT_ARRAY:
        {
          final int length = readSize(buffer);
          final int[] array = new int[length];
          readAlignment(buffer, 4);
          buffer.asIntBuffer().get(array);
          result = array;
          buffer.position(buffer.position() + 4 * length);
          break;
        }
      case LONG_ARRAY:
        {
          final int length = readSize(buffer);
          final long[] array = new long[length];
          readAlignment(buffer, 8);
          buffer.asLongBuffer().get(array);
          result = array;
          buffer.position(buffer.position() + 8 * length);
          break;
        }
      case DOUBLE_ARRAY:
        {
          final int length = readSize(buffer);
          final double[] array = new double[length];
          readAlignment(buffer, 8);
          buffer.asDoubleBuffer().get(array);
          result = array;
          buffer.position(buffer.position() + 8 * length);
          break;
        }
      case LIST:
        {
          final int size = readSize(buffer);
          final List