SizedBox控制元件能強制子控制元件具有特定寬度、高度或兩者都有

import 'package:flutter/material.dart';
class LayoutDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('強制大小'),
      ),
      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控制元件能強制子小部件的寬度和高度具有給定的寬高比，以寬度與高度的比例表示。

import 'package:flutter/material.dart';
class LayoutDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('強制比例'),
      ),
      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(),
    ),
  );
}