从抽屉里调用 setState？

Question

上下文

使用标准的 flutter 演示我添加了一个抽屉。我把抽屉里的东西放在另一个 class 的另一个文件里。两者都是有状态的小部件。我在抽屉中使用了一个浮动操作按钮，setState 增加了主屏幕上显示的数字的全局变量。

会发生什么

当我按下它时没有任何反应。

在我使用主 page/main.dart 上的浮动操作按钮之前，它不会更新主 page/main.dart 上的文本。然后它也添加了我在抽屉中添加的所有增量。

所以它只是没有重建小部件。

如何获取它来重建小部件？我以为你需要的只是它们都在一个 setstate 中？

我想出的最佳可能原因

是否因为即使我在有状态小部件内部使用有状态小部件，setstate 仅适用于嵌入式有状态小部件，因为嵌入式小部件在技术上是 main.dart 中创建的对象？

main.dart

代码

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

DrawerClass _drawer = DrawerClass();

int counter = 0;

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(
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  void _incrementCounter() {
    setState(() {
      counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      endDrawer: SafeArea(child: Drawer(child: Container(child: _drawer,),)),
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          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),
      ),
    );
  }
}

抽屉代码

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

class DrawerClass extends StatefulWidget {
  @override
  _DrawerClassState createState() => _DrawerClassState();
}

class _DrawerClassState extends State<DrawerClass> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Color(0xFF222831),
      body: Container(
        width: 100,
        child: Center(
          child: FloatingActionButton(
            tooltip: 'Increment',
            child: Icon(Icons.add),
            onPressed: () {
              setState(() {
                counter++;
              });
            },
          ),
        ),
      ),
    );
  }
}

Answer 1

只需将 _incrementCounter 传递给 DrawerClass。通过此更改，您的 DrawerClass 现在可以是 StatelessWidget，并且不需要将 counter 和 _drawer 变量设置为全局变量。请看下面的代码：

main.dart

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

//DrawerClass _drawer = DrawerClass();

//int counter = 0;

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(),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int counter = 0;
  void _incrementCounter() {
    setState(() {
      counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    final DrawerClass _drawer = DrawerClass(
      increment: _incrementCounter,
    );
    return Scaffold(
      endDrawer: SafeArea(
          child: Drawer(
        child: Container(
          child: _drawer,
        ),
      )),
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          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),
      ),
    );
  }
}

drawer.dart

import 'package:flutter/material.dart';

class DrawerClass extends StatelessWidget {
  final Function increment;

  const DrawerClass({Key key, this.increment}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Color(0xFF222831),
      body: Container(
        width: 100,
        child: Center(
          child: FloatingActionButton(
            tooltip: 'Increment',
            child: Icon(Icons.add),
            onPressed: increment,
          ),
        ),
      ),
    );
  }
}

从抽屉里调用 setState？

calling setState from drawer?

flutter

dart

flutter-state

上下文

会发生什么