详解Flutter 调用 Android Native 的方法

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 •
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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