Flutter 错误:使用不包含 MediaQuery 的上下文调用 MediaQuery.of()

问题描述

我一直在尝试获取 Flutter 中整个上下文视图的大小.但是每次我尝试时都会遇到上述错误.这是我的代码:

I have been trying to get the size of the whole context view in Flutter. But every time I try I'm getting the above mentioned error. Here's my code:

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {

    final size = MediaQuery.of(context).size;
    return new MaterialApp(
      home: new Scaffold(),
    );
  }
}

注意:我也尝试过使用 StatefulWidget.请帮我找出我在这里做错了什么.

Note: I also tried with a StatefulWidget. Please, help me find what I'm doing wrong here.

推荐答案

您需要一个 MaterialApp 或一个 WidgetsApp 围绕您的小部件.他们提供MediaQuery.当您调用 .of(context) 时，flutter 将始终查找小部件树以找到小部件.

You need a MaterialApp or a WidgetsApp around your widget. They provide the MediaQuery. When you call .of(context) flutter will always look up the widget tree to find the widget.

您通常在 main.dart 中有这个:

You usually have this in your main.dart:

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

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Title',
      theme: kThemeData,
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final size = MediaQuery.of(context).size;

    return Container(
      child: ...,
    );
  }
}

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