android - FlutterView 未在 Android 中显示 Widget UI

Question

我有一个集成了 Flutter 模块的 android SDK。 Dart 代码是来自 Flutter 的基本增量示例。
我正在尝试将 Dart 代码加载到 FlutterView 中。我注意到虽然调用了打印 Dart 代码，但未显示小部件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ffffff"
    android:orientation="vertical">

<io.flutter.embedding.android.FlutterView
    android:id="@+id/flutter_view"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />

</RelativeLayout>

加载 Dart 代码的代码(在 View.OnAttachStateChangeListener 中):

override fun onViewAttachedToWindow(v: View?) {
    v?.run {
        FlutterMain.startInitialization(context)
        FlutterMain.ensureInitializationComplete(context,null);

        val flutterEngine = FlutterEngine(context)
        flutterEngine.dartExecutor.executeDartEntrypoint(
                // set which of dart methode will be used here
                DartExecutor.DartEntrypoint(FlutterMain.findAppBundlePath(), "myMainDartMethod")
                // to set here the main methode you can use this function to do this
                // inteade of DartEntrypoint(FlutterMain.findAppBundlePath(),"myMainDartMethod")
                // write this mdethode DartEntrypoint.createDefault()
                //DartExecutor.DartEntrypoint.createDefault()
        )

        flutterView = findViewById(R.id.flutter_view)
        flutterView.attachToFlutterEngine(flutterEngine)
    }
}

我用过“myMainDartMethod”和 DartExecutor.DartEntrypoint.createDefault() 都不起作用
Dart 代码:

import 'package:flutter/material.dart';

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

@pragma('vm:entry-point') // say the release that this function must alos in the project used and it must not deleted
void myMainDartMethod() => runApp(MyApp()); // I use this function to show in the android activity

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    print("Flutter/MyApp in dart is called");
    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> {
  int _counter = 0;

  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.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

注意实际调用的打印，但 UI 在 Android 端 (FlutterView) 不可见。
我错过了什么？我可以添加/更改什么来显示代码？

Answer 1

问题是我缺少生命周期 channel 状态。
我在 FlutterEngine 实例化之后添加了以下行

val flutterEngine = FlutterEngine(context)
flutterEngine.lifecycleChannel.appIsResumed()
            

当然，您可能需要在正确的位置调用其他生命周期 channel 方法
来源:https://medium.com/@kassan424/sample-example-how-flutterview-in-a-android-activity-can-be-use-b9a887cd1d7