flutter页面布局一

Padding组件

在 html 中常见的布局标签都有 padding 属性，但是 Flutter 中很多 Widget 是没有 padding 属性。这个时候我们可以用 Padding 组件处理容器与子元素直接的间距。 

该组件接收两个属性：

• padding ：padding 值, EdgeInsetss 设置填充的值
• child ：子组件

例如，要实现前面的网格布局里面的单元格之间的间距，就可以使用Padding组件。

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return MaterialApp(
        home: Scaffold(
      appBar: AppBar(title: Text('FlutterDemo')),
      body: LayoutDemo(),
    ));
  }
}

class LayoutDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.fromLTRB(0, 0, 10, 0),
      child: GridView.count(
        crossAxisCount: 2,
        childAspectRatio: 1.7,
        children: <Widget>[
          Padding(
            padding: EdgeInsets.fromLTRB(10, 10, 0, 0),
            child: Image.network('https://img.ivsky.com/img/tupian/li/201810/30/motianlun-005.jpg',
                fit: BoxFit.cover),
          ),
          Padding(
            padding: EdgeInsets.fromLTRB(10, 10, 0, 0),
            child: Image.network('https://img.ivsky.com/img/tupian/li/201811/06/xiaosongshu-002.jpg',
                fit: BoxFit.cover),
          ),
          Padding(
            padding: EdgeInsets.fromLTRB(10, 10, 0, 0),
            child: Image.network('https://img.ivsky.com/img/tupian/li/201811/06/ludeng-006.jpg',
                fit: BoxFit.cover),
          ),
          Padding(
            padding: EdgeInsets.fromLTRB(10, 10, 0, 0),
            child: Image.network('https://img.ivsky.com/img/tupian/li/201811/06/seattle-005.jpg',
                fit: BoxFit.cover),
          ),
          Padding(
            padding: EdgeInsets.fromLTRB(10, 10, 0, 0),
            child: Image.network('https://img.ivsky.com/img/tupian/li/201811/07/osaka-005.jpg',
                fit: BoxFit.cover),
          ),
          Padding(
            padding: EdgeInsets.fromLTRB(10, 10, 0, 0),
            child: Image.network('https://img.ivsky.com/img/tupian/li/201811/07/mushroom.jpg',
                fit: BoxFit.cover),
          ),
        ],
    ));
  }
}

Row 水平布局组件

Row组件用于实现水平布局，相比于ListView的水平排列而言，这个Row的宽度是可控的，二者之间的参数也是不一样的，Row组件技术的参数为：

• mainAxisAlignment ：主轴的排序方式 
• crossAxisAlignment：次轴的排序方式 
• children：组件子元素 

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(
      height: 800.0,
       400.0,
      color: Colors.pink,
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,    
        crossAxisAlignment: CrossAxisAlignment.start,     
        children: <Widget>[
          IconContainer(Icons.search,color: Colors.blue),
          IconContainer(Icons.home,color: Colors.orange),
          IconContainer(Icons.select_all,color: Colors.red),
        ],
      ),
    );
  }
}


class IconContainer extends StatelessWidget{
  double size=32.0;
  Color color=Colors.red;
  IconData icon;
  IconContainer(this.icon,{this.color,this.size});
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Container(
      height: 100.0,
       100.0,
      color: this.color,
      child: Center(
        child: Icon(this.icon,size: this.size,color: Colors.white)
      ),
    );
  }
}

Column 垂直布局组件 

Column组件是区别于Row组件的，用于实现垂直布局，接收的参数和上面的Row是一样的。

class LayoutDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      height: 800.0,
       400.0,
      color: Colors.pink,
      child: Column(    
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        crossAxisAlignment: CrossAxisAlignment.end,   
        children: <Widget>[
          IconContainer(Icons.search,color: Colors.blue),
          IconContainer(Icons.home,color: Colors.orange),
          IconContainer(Icons.select_all,color: Colors.red),
        ],
      ),
    );
  }
}

Expanded组件

Expanded 可以用在 Row 和 Column 布局中 ，用于实现类似web中的Flex布局。

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return MaterialApp(
        home: Scaffold(
      appBar: AppBar(title: Text('FlutterDemo')),
      body: LayoutDemo(),
    ));
  }
}

class LayoutDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Row(    
     
        children: <Widget>[
          Expanded(
            flex: 1,
            child: IconContainer(Icons.search,color: Colors.blue)
          ),
           Expanded(
            flex: 2,
            child: IconContainer(Icons.home,color: Colors.orange),  
          ),
           Expanded(
            flex: 1,
            child: IconContainer(Icons.select_all,color: Colors.red),  
          ),
               
        ],    
    );
  }
}

class IconContainer extends StatelessWidget{
  double size=32.0;
  Color color=Colors.red;
  IconData icon;
  IconContainer(this.icon,{this.color,this.size});
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Container(
      height: 100.0,
       100.0,
      color: this.color,
      child: Center(
        child: Icon(this.icon,size: this.size,color: Colors.white)
      ),
    );
  }
}

上面是实现等分的，既然是类似于Flex的，那么，也可以实现部分固定宽度，剩余部分自适应的效果：

class LayoutDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Row(   
        children: <Widget>[
          Expanded(
            flex: 1,
            child: IconContainer(Icons.home,color: Colors.orange),  
          ),
          IconContainer(Icons.search,color: Colors.blue)
        ],    
    );
  }
}

最后，我们就可以结合上面的知识，实现下面的布局了：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return MaterialApp(
        home: Scaffold(
      appBar: AppBar(title: Text('FlutterDemo')),
      body: LayoutDemo(),
    ));
  }
}

class LayoutDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[

        Row(
          children: <Widget>[
            Expanded(
              child:   Container(
                height: 180,
                color: Colors.black,
                child: Text('你好Flutter'),
              ),
            )
          ],
        ),
        SizedBox(height: 10),
        Row(
          children: <Widget>[
            Expanded(
              flex: 2,
              child: Container(
                height: 180,
                child: Image.network("https://ss3.bdstatic.com/70cFv8Sh_Q1YnxGkpoWK1HF6hhy/it/u=2606512668,2361120991&fm=27&gp=0.jpg",fit: BoxFit.cover),

              )
            ),
            SizedBox( 10),
            Expanded(
              flex: 1,
              child: Container(
                height: 180,
                child: ListView(
                  children: <Widget>[
                    Container(
                      height: 85,
                      child: Image.network("https://ss3.bdstatic.com/70cFv8Sh_Q1YnxGkpoWK1HF6hhy/it/u=2606512668,2361120991&fm=27&gp=0.jpg",fit: BoxFit.cover),

                    ),
                    SizedBox(height: 10),
                    Container(
                      height: 85,
                      child: Image.network("https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=2191520521,2689315141&fm=27&gp=0.jpg",fit: BoxFit.cover),

                    )
                  ],
                )
              )
            ),

          ],
        )
      ],
    );
  }
}