Flutter 调用 Android Native 的方法，是通过MethodChannel的方式来实现的:

在Android端：

• 创建一个Class，实现FlutterPlugin和MethodCallHandler接口
• 重写onAttachedToEngine()，onDetachedFromEngine()，onMethodCall()
• onAttachedToEngine()中，根据自定义的CHANNEL_NAME创建MethodChannel， onDetachedFromEngine中，释放MethodChannel
• onMethodCall中，通过自定义的METHOD_NAME，来响应Flutter中，invokeMethod对Native的通信，代码如下

class MethodChannelPlugin : FlutterPlugin, MethodChannel.MethodCallHandler { private var methodChannel: MethodChannel? = null private var mNoteForFlutterListener: NoteForFlutterListener? = null companion object { private const val CHANNEL_NAME = "method_channel" private const val METHOD_NAME = "saveNote" val instance: MethodChannelPlugin by lazy(mode = LazyThreadSafetyMode.SYNCHRONIZED) { MethodChannelPlugin() } } override fun onAttachedToEngine(binding: FlutterPlugin.FlutterPluginBinding) { methodChannel = MethodChannel(binding.binaryMessenger, CHANNEL_NAME) methodChannel?.setMethodCallHandler(this) } override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) { methodChannel?.setMethodCallHandler(null) methodChannel = null } override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) { if (call.method == METHOD_NAME) { val content = call.argument<String>("content") mNoteForFlutterListener?.sendData(content!!) result.success("success") } else { result.notImplemented() } } fun setListener(noteForFlutterListener: NoteForFlutterListener) { mNoteForFlutterListener = noteForFlutterListener }

在Flutter端：

• 根据Native中定义的METHOD_NAME来创建MethodChannel
• 通过MethodChannel.invokeMethod(METHOD_NAME,params)，参数METHOD_NAME为Native中定义的METHOD_NAME，params为传递的参数，就可以和Native进行通信了，在Native的onMethodCall方法中，通过call.method == METHOD_NAME来确定，Flutter是否调用的是Native中定义的METHOD_NAME的方法，代码如下

class NoteMainFulState extends State<NoteMainFul> { //flutter 和 native 通信 static const _methodMessageChannel = MethodChannel("method_channel"); TextField textField; TextEditingController textEditingController; @override Widget build(BuildContext context) { return Scaffold( body: Container( margin: EdgeInsets.fromLTRB(20.0, 60.0, 20.0, 20.0), child: Column( children: [ Container( child: Column( children: [ textField = TextField( //去掉下划线 decoration: InputDecoration(border: InputBorder.none), enabled: true, controller: textEditingController = NoteTextEditingController(), keyboardType: TextInputType.multiline, textInputAction: TextInputAction.newline, maxLines: null, ), RichText( text: TextSpan(), ), ], ), ), Container( color: Colors.deepPurple, height: 50, child: Row( mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [ GestureDetector( child: Icon( Icons.forward, ), onTap: clickOut, ) ], ), ) ], ), ), ); } void clickOut() async { //调用native方法，返回首页 var content = textEditingController.text; Map<String, dynamic> map = {"content": content}; var result = await _methodMessageChannel.invokeMethod("saveNote", map); print("result $result"); }

以上就是Flutter 调用 Android Native 的方法的过程，有时间再分析下他们的实现原理
待续....
附，我当前的Flutter版本是 ：
Flutter 1.22.3 • channel stable • https://github.com/flutter/flutter
Framework • revision 8874f21e79 (3 months ago) • 2020-10-29 14:14:35 -0700
Engine • revision a1440ca392
Tools • Dart 2.10.3

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