Flutter基础—定位对齐之大小比例

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SizedBox控件能强制子控件具有特定宽度、高度或两者都有

import 'package:flutter/material.dart';class LayoutDemo extends StatelessWidget {  @override  Widget build(BuildContext context) {    return new Scaffold(      appBar: new AppBar(        title: new Text('强制大小'),      ),      body: new SizedBox(        width: 250.0,        height: 250.0,        child: new Container(          decoration: new BoxDecoration(            backgroundColor: Colors.lightBlueAccent[100],          ),        ),      ),    );  }}void main() {  runApp(    new MaterialApp(      title: 'Flutter教程',      home: new LayoutDemo(),    ),  );}

AspectRatio控件能强制子小部件的宽度和高度具有给定的宽高比，以宽度与高度的比例表示。

import 'package:flutter/material.dart';class LayoutDemo extends StatelessWidget {  @override  Widget build(BuildContext context) {    return new Scaffold(      appBar: new AppBar(        title: new Text('强制比例'),      ),      body: new AspectRatio(        aspectRatio: 3.0 / 2.0,        child: new Container(          decoration: new BoxDecoration(            backgroundColor: Colors.lightBlueAccent[100],          ),        ),      ),    );  }}void main() {  runApp(    new MaterialApp(      title: 'Flutter教程',      home: new LayoutDemo(),    ),  );}

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