未處理的異常：MissingPluginException（在通道 * 上找不到方法 getBatteryLevel 的實現）與 flutter1.12

Question

我們最近遷移到了flutter1.12 ，我們認為它使用了 Add2App 功能，但是當開始測試方法通道時，它總是給我一個錯誤說

未處理的異常：MissingPluginException（在頻道 com.app.test/channel 上找不到方法 getBatteryLevel 的實現）

我試圖通過創建一個模塊來使用相同的代碼仍然沒有運氣。 有人可以幫助我理解這個問題並獲得相同的解決方案。

這是我一直在嘗試的

我的main.dart 代碼

    import 'package:flutter/material.dart';
    import 'package:flutter/services.dart';

    void main() => runApp(MyApp());

    class MyApp extends StatelessWidget {
    // This widget is the root of your application.
    @override
    Widget build(BuildContext context) {
     return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or press Run > Flutter Hot Reload in a Flutter IDE). Notice that the
        // counter didn't reset back to zero; the application is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
    }
   }

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
 }

class _MyHomePageState extends State<MyHomePage> {
  static const platform = const MethodChannel("com.app.test/channel");
  int _counter = 0;

  String _batteryLevel = 'Unknown battery level.';

  Future<void> _getBatteryLevel() async {
    String batteryLevel;
    try {
      final int result = await platform.invokeMethod('getBatteryLevel');
      batteryLevel = 'Battery level at $result % .';
    } on PlatformException catch (e) {
      batteryLevel = "Failed to get battery level: '${e.message}'.";
    }

    setState(() {
      _batteryLevel = batteryLevel;
    });
  }
  void _incrementCounter() {

    setState(() {

      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),

            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
            RaisedButton(
              child: Text('Get Battery Level'),
              onPressed: _getBatteryLevel,
            ),
            Text(_batteryLevel),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

這是我的MainActivity.java ，其中存在獲取電池電量的實際方法

import android.content.ContextWrapper;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.BatteryManager;
import android.os.Build.VERSION;
import android.os.Build.VERSION_CODES;
import android.os.Bundle;

import java.nio.ByteBuffer;

import androidx.annotation.NonNull;
import io.flutter.embedding.android.FlutterActivity;
import io.flutter.embedding.engine.FlutterEngine;
import io.flutter.plugin.common.BinaryMessenger;
import io.flutter.plugin.common.MethodCall;
import io.flutter.plugin.common.MethodChannel;
import io.flutter.plugins.GeneratedPluginRegistrant;


public class MainActivity extends FlutterActivity {

    @Override
    public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine);
    }
    private int getBatteryLevel() {
        int batteryLevel = -1;
        if (VERSION.SDK_INT >= VERSION_CODES.LOLLIPOP) {
            BatteryManager batteryManager = (BatteryManager) getSystemService(BATTERY_SERVICE);
            batteryLevel = batteryManager.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY);
        } else {
            Intent intent = new ContextWrapper(getApplicationContext()).
                    registerReceiver(null, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
            batteryLevel = (intent.getIntExtra(BatteryManager.EXTRA_LEVEL, -1) * 100) /
                    intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1);
        }

        return batteryLevel;
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);


        BinaryMessenger binaryMessenger = new BinaryMessenger() {
            @Override
            public void send(String channel, ByteBuffer message) {
            }

            @Override
            public void send(String channel, ByteBuffer message, BinaryReply callback) {

            }

            @Override
            public void setMessageHandler(String channel, BinaryMessageHandler handler) {

            }
        };
        new MethodChannel(binaryMessenger, "com.app.test/channel").setMethodCallHandler(
                new MethodChannel.MethodCallHandler() {
                    @Override
                    public void onMethodCall(MethodCall call, MethodChannel.Result result) {
                        if (call.method.equals("getBatteryLevel")) {
                            int batteryLevel = getBatteryLevel();

                            if (batteryLevel != -1) {
                                result.success(batteryLevel);
                            } else {
                                result.error("UNAVAILABLE", "Battery level not available.", null);
                            }
                        } else {
                            result.notImplemented();
                        }
                    }
                });
    }
}

過去 2 天我一直在思考這個問題，因為我已經嘗試了很多可能的修復方法，例如 flutter clean 和 flutter pub cache repair 以及我可以使用的所有其他選項。

Answer 1

最后，我能夠通過替換以下代碼來使其工作。 文檔中沒有提到這一點，如果有人遇到同樣的問題，這可能會很方便

public class MainActivity extends FlutterActivity {

    @Override
    public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine);
        new MethodChannel(flutterEngine.getDartExecutor(), "com.app.test/channel").setMethodCallHandler(
                new MethodChannel.MethodCallHandler() {
                    @Override
                    public void onMethodCall(MethodCall call, MethodChannel.Result result) {
                        if (call.method.equals("getBatteryLevel")) {
                            int batteryLevel = getBatteryLevel();

                            if (batteryLevel != -1) {
                                result.success(batteryLevel);
                            } else {
                                result.error("UNAVAILABLE", "Battery level not available.", null);
                            }
                        } else {
                            result.notImplemented();
                        }
                    }
                });

    }
    private int getBatteryLevel() {
        int batteryLevel = -1;
        if (VERSION.SDK_INT >= VERSION_CODES.LOLLIPOP) {
            BatteryManager batteryManager = (BatteryManager) getSystemService(BATTERY_SERVICE);
            batteryLevel = batteryManager.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY);
        } else {
            Intent intent = new ContextWrapper(getApplicationContext()).
                    registerReceiver(null, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
            batteryLevel = (intent.getIntExtra(BatteryManager.EXTRA_LEVEL, -1) * 100) /
                    intent.getIntExtra(BatteryManager.EXTRA_SCALE, -1);
        }

        return batteryLevel;
    }


    }

最初，我使用 binaryMessenger 作為方法通道，但這就是問題所在
我用new MethodChannel(flutterEngine.getDartExecutor(), "com.app.test/channel")替換了下面的代碼new MethodChannel(binaryMessenger, "com.app.test/channel") new MethodChannel(flutterEngine.getDartExecutor(), "com.app.test/channel")

根據文檔

使用 DartExecutor 連接任何需要的消息通道和方法通道 * 以促進 Android 和 Dart/Flutter 之間的通信。