如何将颤动页面（小部件）重置为初始状态（应用程序首次构建时的状态）

Question

假设我的页面上有一些滑块和开关，我更改了它们的状态并修改了它们，我知道我们执行setState来显示小部件树的更改状态并重建它，但我想知道是否有办法撤消所有这些更改并返回到初始状态（应用程序最初构建时的状态）？

Answer 1

如果你想开箱即用

---

void main() => runApp(MaterialApp(home: DummyWidget()));

class DummyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) => HomePage();
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  bool _enabled = false; // For Switch
  double _value = 0; // For Slider

  // This is the trick!
  void _reset() {
    Navigator.pushReplacement(
      context,
      PageRouteBuilder(
        transitionDuration: Duration.zero,
        pageBuilder: (_, __, ___) => DummyWidget(),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: [
          Switch(
            value: _enabled,
            onChanged: (newValue) => setState(() => _enabled = newValue),
          ),
          Slider(
            value: _value,
            onChanged: (newValue) => setState(() => _value = newValue),
          ),
          FlatButton(
            onPressed: _reset,
            child: Text('RESET'),
          ),
        ],
      ),
    );
  }
}

更好的方法可能是使用密钥。 这是关键方法

Answer 2

一个简单的技巧是使用相同的路线弹出和推送。 像这样：

Navigator.popAndPushNamed(context, "same_route");

Answer 3

截屏：

---

使用key来改变状态。

void main() => runApp(MaterialApp(home: HomePage()));

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int _count = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: KeyedSubtree(
        key: ValueKey<int>(_count),
        child: Column(
          children: [
            MainPage(),
            FlatButton(
              onPressed: () => setState(() => ++_count),
              child: Text('RESET'),
            )
          ],
        ),
      ),
    );
  }
}

class MainPage extends StatefulWidget {
  @override
  _MainPageState createState() => _MainPageState();
}

class _MainPageState extends State<MainPage> {
  bool _enabled = false; // For Switch
  double _value = 0; // For Slider.

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Switch(
          value: _enabled,
          onChanged: (newValue) => setState(() => _enabled = newValue),
        ),
        Slider(
          value: _value,
          onChanged: (newValue) => setState(() => _value = newValue),
        ),
      ],
    );
  }
}

Answer 4

这是重置为初始数据的众多方法中的一种

import 'package:flutter/material.dart';

List<String> initialData = ['First', 'Second', 'Third'];

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark(),
      home: Example(),
    );
  }
}

class Example extends StatefulWidget {
  @override
  _ExampleState createState() => _ExampleState();
}

class _ExampleState extends State<Example> {
  List<String> items = [];

  @override
  void initState() {
    fillInitialData();
    super.initState();
  }

  fillInitialData() {
    items.addAll(initialData);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Example')),
      body: Column(
        children: <Widget>[
          Expanded(
            child: ListView.builder(
              itemCount: items.length,
              itemBuilder: (context, index) {
                return Card(
                  child: Padding(
                    padding: EdgeInsets.all(16.0),
                    child: Text(items[index]),
                  ),
                );
              },
            ),
          ),
          Row(
            children: <Widget>[
              FlatButton(
                onPressed: () {
                  setState(() {
                    items.add('A new item');
                  });
                },
                child: Text('Add an item'),
              ),
              FlatButton(
                onPressed: () {
                  setState(() {
                    items.clear();
                    fillInitialData();
                  });
                },
                child: Text('Reset'),
              ),
            ],
          ),
        ],
      ),
    );
  }
}

Answer 5

截屏：

完整代码：

void main() {
  runApp(
    MaterialApp(
      // Passing initial values
      home: HomePage(enabled: false, value: 0),
    ),
  );
}

class HomePage extends StatefulWidget {
  final bool enabled;
  final double value;

  HomePage({this.enabled = false, this.value = 0});

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

class _HomePageState extends State<HomePage> {
  bool _initialEnabled, _enabled; // For Switches
  double _initialValue, _value; // For Sliders

  @override
  void initState() {
    super.initState();

    // Assign them once (initial data)
    _initialEnabled ??= widget.enabled;
    _initialValue ??= widget.value;

    // These values can be changed by respective widgets
    _enabled = _initialEnabled;
    _value = _initialValue;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Padding(
        padding: const EdgeInsets.all(20),
        child: Column(
          children: [
            Switch(
              value: _enabled,
              onChanged: (value) => setState(() => _enabled = value),
            ),
            Slider(
              value: _value,
              onChanged: (value) => setState(() => _value = value),
            ),
            RaisedButton(
              onPressed: () {
                setState(() {
                  // Resetting the values to initial ones which were passed
                  _enabled = _initialEnabled;
                  _value = _initialValue;
                });
              },
              child: Text('RESET'),
            ),
          ],
        ),
      ),
    );
  }
}

Answer 6

您可以调用YourStateClass.initState()以恢复到其原始初始化状态。

还要确保在构造状态时，您需要在void initState()函数中初始化所有变量。

前任。

class FooState extends State<Foo> { 
    int someVariable;

    @override
    void initState() {
        someVariable = 0;
    }
}

您需要在initState()函数中为所有变量分配一个值才能使其正常工作。

有关更多信息，请查看以下文档： https : //api.flutter.dev/flutter/widgets/State/initState.html

Answer 7

在这种情况下，有几种古老的设计模式可能很有用。 有一个重置选项很酷，但更酷的是undo 。

通过以下教程了解如何在 Flutter 中实现命令和备忘录模式： 命令| 纪念