AspectRatio 的作用是根据设置调整子元素 child 的宽高比。

AspectRatio 首先会在布局限制条件允许的范围内尽可能的扩展，widget 的高度是由宽度和比率

aspectRatio 

决定的，类似于 BoxFit 中的 contain，按照固定比率去尽量占满区域。如果在满足所有限制条件过后无法找到一个可行的尺寸，AspectRatio 最终将会去优先适应布局限制条件，而忽略所设置的比率。

import 'package:flutter/material.dart';void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(title: Text('FlutterDemo')),
body: LayoutDemo(),
));
}
}
class LayoutDemo extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Container(
width: 200,
child: AspectRatio(
aspectRatio: 2.0/1.0,
child: Container(
color: Colors.red,
),
),

);  

}
}

在上面的例子中，给组件的父级设置了宽度200，然后设置该组件的宽高比为2:1，这样就得到了一个宽200，高100的容器，但是更多的时候，是用来做平铺的。

Card 是卡片组件块，内容可以由大多数类型的 Widget 构成，Card 具有圆角和阴影，这让它看起来有立体感。该组件有三个常用的可选参数：

• margin ：外边距
• child：子组件
• Shape ：Card 的阴影效果，默认的阴影效果为圆角的长方形边。

class LayoutDemo extends StatelessWidget {
@override
Widget build(BuildContext context) {
// TODO: implement build
return ListView(
children: [
Card(
margin: EdgeInsets.all(10),
child: Column(
children: [
ListTile(
title:Text("张三",style: TextStyle(fontSize: 28)) ,
subtitle: Text("高级工程师"),
),
ListTile(title:Text("电话：xxxxx") , ),
ListTile(title:Text("地址：xxxxxx") ,)
],
),
),
Card(
margin: EdgeInsets.all(10),
child: Column(
children: [
ListTile(
title:Text("李四",style: TextStyle(fontSize: 28)) ,
subtitle: Text("高级工程师"),
),
ListTile(title:Text("电话：xxxxx") , ),
ListTile(title:Text("地址：xxxxxx") ,)
],
),
),
Card(
margin: EdgeInsets.all(10),
child: Column(
children: [
ListTile(
title:Text("王五",style: TextStyle(fontSize: 28)) ,
subtitle: Text("高级工程师"),
),
ListTile(title:Text("电话：xxxxx") , ),
ListTile(title:Text("地址：xxxxxx") ,)
],
),
),
],
);
}
}

card下的图文混排

class LayoutDemo extends StatelessWidget {
@override
Widget build(BuildContext context) {
List listData=[
{
"title": 'Candy Shop',
"author": 'Mohamed Chahin',
"imageUrl": 'https://www.itying.com/images/flutter/1.png',
"description": 'Flutter is Google’s mobile UI framework for crafting high-quality native experiences on iOS and Android in record time. Flutter works with existing',
},
{
"title": 'Childhood in a picture',
"author": 'Google',
"imageUrl": 'https://www.itying.com/images/flutter/2.png',
"description": 'Flutter is Google’s mobile UI framework for crafting high-quality native experiences on iOS and Android in record time. Flutter works with existing',
},
];
return ListView(
children: listData.map((value){
return Card(
margin: EdgeInsets.all(10),
child:Column(
children: [
AspectRatio(
aspectRatio: 20/9,
child: Image.network(value["imageUrl"],fit: BoxFit.cover,),
),
ListTile(
leading: CircleAvatar(
backgroundImage:NetworkImage(value["imageUrl"])
),
title: Text(value["title"]),
subtitle: Text(value["description"],maxLines: 1,overflow: TextOverflow.ellipsis),
)
],
),

    );

  }).toList(),  
);  

}
}