Flutter 总是重启而不是热重载

Question

我在 Windows 10 上安装了 Flutter 2.2 并将 Flutter 扩展添加到 VSCode。在启动新项目时，我可以运行由 Flutter 扩展创建的样板代码。

在代码中有一条评论鼓励您尝试热重载。请参阅下面的代码，您可以在其中将 Primary Swatch 更改为与蓝色不同的颜色。

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  String name = 'Paps';

  @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 simply save your changes to "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, required 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.arrow_circle_down),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

问题在于它总是在更改时重新启动应用程序，而不是热重载。

我已尝试 F5 进行调试，也尝试 Ctrl-F5 启动而不进行调试。我还从命令行尝试了flutter run，然后按下r。输出总是一样的：

Restarted application in 490ms.
Restarted application in 224ms.
Restarted application in 218ms.

因此，每次我对代码进行更改时，应用程序状态都会丢失。关于可能出错的任何想法？

Answer 1

网络上目前不支持热重载。你可以参考这个FAQ

Answer 2

其实 Flutter in web 直到现在都不支持热重载： 如果您想要热重载以提高时间效率，请使用 android 或 ios 模拟器。您还可以使用像 ld player 这样的低规格模拟器： https://www.ldplayer.net/

Answer 3

你应该降级你的 Flutter 版本命令在这里

在 Flutter 安装目录下执行

git checkout v0.1.9

then run

flutter doctor

您可以在 Flutter GitHub 存储库https://github.com/flutter/flutter 中查看哪些版本可用