详解Flutter 调用 Android Native 的方法

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("content")
      mNoteForFlutterListener?.sendData(content!!)
      result.success("success")
    } else {
      result.notImplemented()
    }
  }

  fun setListener(noteForFlutterListener: NoteForFlutterListener) {
    mNoteForFlutterListener = noteForFlutterListener
  }

class NoteMainFulState extends State {
 //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 map = {"content": content};
  var result = await _methodMessageChannel.invokeMethod("saveNote", map);
  print("result $result");
 }