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

问题描述

我一直试图在Flutter中获取整个上下文视图的大小。但是，每次尝试时，我都会遇到上述错误。
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：我也尝试使用 StatefulWidget 。
请帮我在这里找到我在做错什么。

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

推荐答案

您需要一个您的小部件周围的> MaterialApp 或 WidgetsApp 。他们提供了 MediaQuery 。当您调用 .of（context）时，flutter会始终在小部件树中查找该小部件。

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.

您通常在您的main.dart中有以下内容：

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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