mFlutter2MethodChannel = new MethodChannel(flutter2Engine.getDartExecutor(), "flutter2/flutter2Java");//字符串的含义跟JsBridge中的js和native互相调用的含义差不多，flutter中要是用这个消息通道时，也要设置为一样的
 mFlutter2MethodChannel.setMethodCallHandler(new MethodChannel.MethodCallHandler() {
     @Override
     public void onMethodCall(MethodCall call, MethodChannel.Result result) {
         if (call == null || result == null){
             if (result!=null){
                 result.error("-1","MethodCall is null",new Exception("MethodCall is null"));
             }
             return;
         }
         if ("getJavaMethod".equals(call.method)){
             result.success("success ");
         } else {
             result.success(" unKnow");
         }
     }
 });

static const platform = const MethodChannel("flutter2/flutter2Java");//跟安卓代码中设置的通道名称字符串一样
Future<Null> _getJavaMethod() async {
  String str;
  try {
    print("dart -_getJavaMethod");
      //在通道上调用此方法
    final String intValue = await platform.invokeMethod("getJavaMethod");//这个参数是跟安卓协商的，相当于一个变量名，安卓用来筛选flutter需要调用的方法用的
    str = ‘getJavaMethod  $intValue .‘;
  } on Exception catch (e) {
    str = "Failed to getJavaMethod: ‘${e.toString()}‘.";
  }
  setState(() {
    print("dart -setState");
    _counter = str;
  });
}