Flutter 项目在 Android 中集成 Flutter module，Flutter 页面通过 MethodChannel 调用 Android 方法时抛出 MissingPluginException

在学习 Flutter，被一个问题折腾了好几天了，问题简化如下：

Flutter 版本是 v1.17.0；

现有 Android 工程，里面有两个 Activity：

1. MainActivity，该 Activity 中有一个按钮
2. NativeActivity 。

然后又按照官方文档集成了 Flutter module，里面有页面 FlutterRoute，FlutterRoute 中有一个按钮。

现在操作逻辑如下： 点击 MainActivity 中的按钮，跳转到 Flutter 页面，然后点击 FlutterRoute 中的按钮，再跳转到 NativeActivity 。

现在 MainActivity 代码如下：

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import androidx.annotation.NonNull;
import io.flutter.embedding.android.FlutterActivity;
import io.flutter.embedding.engine.FlutterEngine;
import io.flutter.plugin.common.MethodCall;
import io.flutter.plugin.common.MethodChannel;
import io.flutter.plugins.GeneratedPluginRegistrant;
public class MainActivity extends FlutterActivity implements View.OnClickListener, MethodChannel.MethodCallHandler {
private Button button;
private static final String CHANNEL_NAME = "TEST_CHANNEL_NAME";
private MethodChannel channel;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    button = findViewById(R.id.button);
    button.setOnClickListener(this);


}

@Override
public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
    super.configureFlutterEngine(flutterEngine);
    GeneratedPluginRegistrant.registerWith(flutterEngine);
    channel = new MethodChannel(flutterEngine.getDartExecutor().getBinaryMessenger(), CHANNEL_NAME);
    channel.setMethodCallHandler(this);
}

@Override
public void onClick(View v) {
    startActivity(
            FlutterActivity.withNewEngine().build(this)
    );
}


@Override
public void onMethodCall(@NonNull MethodCall methodCall, @NonNull MethodChannel.Result result) {
    if ("startNativeActivity".equals(methodCall.method)) {
        Intent intent = new Intent(MainActivity.this, NativeActivity.class);
        startActivity(intent);
    }
}
}

Flutter 代码如下：

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
void main(){
runApp(
MaterialApp(
routes: {
“/”:(BuildContext context)=>FlutterRoute(),
},
initialRoute: “/”,
)
);
}
class FlutterRoute extends StatefulWidget {
FlutterRouteState createState() {
return FlutterRouteState();
}
}
class FlutterRouteState extends State<FlutterRoute> {
static const channel = MethodChannel(“TEST_CHANNEL_NAME”);
Future<void> startNativeActivity() async{
await channel.invokeMethod(“startNativeActivity”);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(“Flutter 页面”),
),
body: Container(
color: Colors.lightGreenAccent,
child: Center(
child: Column(
children: <Widget>[
Text(“Flutter 页面”),
MaterialButton(
color: Colors.redAccent,
child: Text(“跳转到原生 Activity”),
onPressed: () {
startNativeActivity();
},
),
],
),
),
),
);
}
}

在 MainActivity 中点击按钮，可以跳转到 FlutterRoute，但是在 FlutterRoute 中点击按钮跳转到 NativeActivity 的时候却抛出：

E/flutter: [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: MissingPluginException(No implementation found for method startNativeActivity on channel TEST_CHANNEL_NAME)
    #0      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:154:7)
    <asynchronous suspension>
    #1      MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:329:12)
    #2      FlutterRouteState.startNativeActivity (package:fluttermodule/main.dart:27:19)
    #3      FlutterRouteState.build.<anonymous closure> (package:fluttermodule/main.dart:46:19)
    #4      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:779:19)
    #5      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:862:36)
    #6      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
    #7      TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:504:11)
    #8      BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:282:5)
    ......

究竟是哪里出了问题啊，折腾好几天了，始终不行，难道 MethodChannel 不是这么用的吗？

百度谷歌官方 githubStackOverflow 搜了个遍。。。

实在没辙了，求点醒求指教，感谢