Flutter 布局 - BoxConstraints：容器不会缩小到 maxWidth 以下

Posted 2023-02-23

【中文标题】Flutter 布局 - BoxConstraints：容器不会缩小到 maxWidth 以下

【英文标题】：Flutter Layout - BoxConstraints: Container won't shrink below maxWidth

【发布时间】：2020-03-11 00:39:54

【问题描述】：

我仍然在颤振中挣扎。我喜欢它，但是这个看起来应该很简单。

Row(
   mainAxisAlignment: MainAxisAlignment.center,
   children: <Widget>[
     Card(
      child: Container(
        constraints: BoxConstraints(maxWidth: 600,minHeight: 150),  
       ),
     )
   ]
)

所以我想做的是当屏幕更小时卡片缩小，但它停在 600。这对我来说似乎倒退了，

所以这里的卡做我想要的。

但在这里它给了我溢出的错误。

我觉得这需要 1 分钟，但我错过了一些东西。非常感谢任何帮助。

【参考方案1】：

用灵活的作品包装卡片 代码sn-p

Row(mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[
              Flexible(
                child: Card(
                  child: Container(
                    constraints: BoxConstraints(maxWidth: 600, minHeight: 150),
                  ),
                ),
              ),
            ]),

demo，设置容器颜色为蓝色，查看效果更方便

完整代码

    import 'package:flutter/material.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 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, 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>[
            Row(mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[
              Flexible(
                child: Card(
                  child: Container(
                    color: Colors.blue,
                    constraints: BoxConstraints(maxWidth: 600, minHeight: 150),
                  ),
                ),
              ),
            ]),
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  

【讨论】：

我知道这很容易谢谢！你能向我解释一下为什么会这样吗？

你可以参考这个***.com/questions/52645944/…Rémi Rousselet 的回答