CSS:CSS弹性盒子布局 Flexible Box

一、简介

flexbox:全称Flexible Box, 弹性盒子布局。可以简单实现各种伸缩性的设计,它是由伸缩容器和伸缩项目组成。任何一个元素都可以指定为flexbox布局。这种新的布局方案在2009年是由W3C组织提出来的,在此之前,Web开发一般使用基于盒子模型的传统页面布局,依赖定位属性、流动属性和显示属性来解决,参看链接:https://www.cnblogs.com/XYQ-208910/p/5810673.html。弹性盒子布局的出现,极大的方便了开发者,在如今的ReactNative开发中,也已经被引入使用。

伸缩流布局结构图如下:

弹性盒子布局具备的特征:

1、伸缩容器的子元素称为伸缩项目,伸缩项目使用伸缩布局来排版。伸缩布局和传统布局不一样,它按照伸缩流方向布局。

2、伸缩容器由两条轴构成,分别为主轴(main axis)和交叉轴(cross axis)。主轴既可以用水平轴,也可以是竖直轴,根据开发者需要来决定。

3、主轴的起点叫main start,终点叫main end,主轴的空间用main size表示。

4、交叉轴的起点叫cross start,终点叫cross end,交叉轴的空间用cross size表示。

5、默认情况下,伸缩项目总是沿着主轴方向排版,从开始位置到终点位置。至于换行显示,则通过设置伸缩属性来实现。

6、伸缩容器的属性有:display、flex-direction、flex-wrap、flex-flow、justify-content、align-items、align-content

7、伸缩项目的属性有: order、flex-grow、flex-shrink、flex-basis、flex、align-self

 

二、伸缩容器的属性,全局设置排版

HTML:[注意:下面的演示截图项目个数会根据需要选择性注释“flex-item”,有时用不到5个]

<!DOCTYPE html>
<html>
<head>
    <title>Flexbox</title>
    <!--  采用外联方式导入css文件 -->
    <link rel="stylesheet" type="text/css" href="./css_test.css">
</head>
<body>
    <span class="flex-container"> 
        <span class="flex-item" id="item1" style="color:white;font-size:20px">1</span>
        <span class="flex-item" id="item2" style="color:white;font-size:20px">2</span>
        <span class="flex-item" id="item3" style="color:white;font-size:20px">3</span>
        <span class="flex-item" id="item4" style="color:white;font-size:20px">4</span>
        <span class="flex-item" id="item5" style="color:white;font-size:20px">5</span>
    </span>
</body>
</html> 

1、display:决定元素是否为伸缩容器

  • flex:产生块级伸缩容器
    .flex-container {
         display: flex;
     }
  • inline-flex:产生行内块级伸缩容器
  •  .flex-container {
         display: inline-flex;
     }

2、flex-direction:指定伸缩容器主轴的方向

  • row:水平方向,从左到右
     .flex-container {
         display: flex;
         flex-direction: row;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px; 
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • row-reverse:水平方向,从右到左
     .flex-container {
         display: flex;
         flex-direction: row-reverse;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px; 
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • column:竖直方向,从上到下
     .flex-container {
         display: flex;
         flex-direction: column;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px; 
         background-color: green;
         margin: 1px;
     }

  • column-reverse:竖直方向,从下到上
     .flex-container {
         display: flex;
         flex-direction: column-reverse;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px; 
         background-color: green;
         margin: 1px;
     }

3、flex-wrap:指定伸缩容器主轴方向空间不足时,决定是否换行以及换行方式

  • nowarp:不换行
    .flex-container {
         display: flex;
         flex-direction: row;
         flex-wrap: nowrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px; //下图单行状态宽度被重新计算
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • warp:换行,若主轴为水平方向,换行方向是从上到下
     .flex-container {
         display: flex;
         flex-direction: row;
         flex-wrap: wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • wrap-reverse:换行,若主轴为水平方向,换行方向是从下到上
     .flex-container {
         display: flex;
         flex-direction: row;
         flex-wrap: wrap-reverse;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

4、flex-flow:flex-direction和flex-wrap的缩写,同时指定伸缩容器主轴方向和换行设置

  • row nowrap:默认主轴是水平方向,从左到右,且不换行
     .flex-container {
         display: flex;
         flex-flow: row nowrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px; //下图单行状态宽度被重新计算
         height: 50px;
         background-color: green;
         margin: 1px;
     }

5、justify-content:决定伸缩项目沿着主轴线的对齐方式

  • flex-start:与主轴线起始位置靠齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         justify-content: flex-start;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • flex-end:与主轴线结束位置靠齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         justify-content: flex-end;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • center:与主轴线中间位置靠齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         justify-content: center;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • space-between:平均分配到主轴线里,第一个项目靠齐起始位置,最后一个项目靠齐终点位置
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         justify-content: space-between;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • sapce-around:平均分配到主轴线里,两端保留一半的空间
    .flex-container {
         display: flex;
         flex-flow: row wrap;
         justify-content: space-around;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

6、align-items:决定伸缩项目不能换行时沿着交叉轴线的对齐方式

  • flex-start:与交叉轴线起始位置靠齐
     .flex-container {
         display: flex;
         flex-flow: row nowrap;
         align-items: flex-start;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px; //下图单行状态宽度被重新计算
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • flex-end:与交叉轴线结束位置靠齐
     .flex-container {
         display: flex;
         flex-flow: row nowrap;
         align-items: flex-end;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px; //下图单行状态宽度被重新计算
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • center:与交叉轴线中间位置靠齐
     .flex-container {
         display: flex;
         flex-flow: row nowrap;
         align-items: center;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • baseline:根据基线对齐
     .flex-container {
         display: flex;
         flex-flow: row nowrap;
         align-items: baseline;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item1 {
         padding-top: 25px;
     }
    
     #item2 {
         padding-top: 20px;
     }
      
     #item3 {
         padding-top: 15px;
     }
    
     #item4 {
         padding-top: 10px;
     }
      
     #item5 {
         padding-top: 5px;
     }

  • stretch:沿着交叉轴线拉伸填充整个伸缩容器
     .flex-container {
         display: flex;
         flex-flow: row nowrap;
         align-items: stretch;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;//此时可以设置宽度,但不能设置高度,否则无法拉伸
         background-color: green;
         margin: 1px;
     }

7、align-content:决定伸缩项目可以换行时沿着交叉轴线的对齐方式,flex-warp:warp一定要开启

  • flex-start:与交叉轴线起始位置靠齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         align-content:flex-start;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • flex-end:与交叉轴线结束位置靠齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         align-content:flex-end;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • center:与主轴线中间位置靠齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         align-content:center;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • space-between:平均分配到主轴线里,第一行项目靠齐起始位置,最后一行项目靠齐终点位置
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         align-content:space-between;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • sapce-around:所有行平均分配到主轴线里,两端保留一半的空间
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         align-content:space-around;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }

  • stretch:沿着交叉轴
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         align-content:stretch;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px; //不要设置高度,不然无法拉伸
         background-color: green;
         margin: 1px;
     }

 

三、伸缩项目的属性,单个设置排版

1、order:定义伸缩项目的排列顺序。数值越小,排列越靠前,默认值为0。

  • 表达式 order: integer;
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item4 {
         order: -1;
     }
    
     #item5 {
         order: -2;
     }

2、flex-grow:定义伸缩项目的放大比例,默认值为0,表示即使存在剩余空间,也不放大。

  • 表达式 flex-grow: number;
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item2 {
         flex-grow: 1; //空间不足,item2不会放大
     }
    
     #item4 {
         flex-grow: 1; //item4放大填满剩余空间
     }

3、flex-shrink:定义伸缩项目的收缩比例,默认值为1。

  • 表达式 flex-shrink: numer;
    .flex-container {
         display: flex;
         flex-flow: row nowrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item4 {
         flex-shrink:3; //单行,空间有限,item4缩小为原来的1/3
     }
    
     #item5 {
         flex-shrink:4;  //单行,空间有限,item5缩小为原来的1/5
    }

4、flex-basis:定义伸缩项目的基准值,剩余空间按照比例进行伸缩,默认auto。

  •  auto
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item5 {
         flex-basis:auto;
     }

            

  • flex-basis: length 
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item5 {
         flex-basis:200px;
     }

5、flex:是flex-grow、flex-shrink、flex-basis的缩写,默认值 0 1 auto。

  • none: 不设置
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item2 {
         flex: none; /* 等同于 flex: 0 0 auto */
     }

  • flex-grow flex-shrink flex-basis: 设置放大或缩小或基准线
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item2 {
         flex: 1; /* 等同于 flex: 1 1 auto 或者 等同于 flex: auto*/
     }

6、align-self:用来设置伸缩项目在交叉轴的对齐方式。

  • auto:自动对齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item3 {
         align-self: auto;
     }

  • flex-start: 向交叉轴的开始位置对齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item3 {
         align-self: flex-start;
     }

  • flex-end: 向交叉轴的结束位置对齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item3 {
         align-self: flex-end;
     }

  • center: 向交叉轴的中间位置对齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item3 {
         align-self: center;
     }

  • baseline:向交叉轴的基准线对齐
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         height: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item1 {
         align-self: baseline;
         margin-top: 50px;
     }
    
     #item2 {
         align-self: baseline;
     }

  • stretch: 在交叉轴拉伸填满伸缩容器
     .flex-container {
         display: flex;
         flex-flow: row wrap;
         width: 160px;
         height: 160px;
         background-color: red;
     }
    
     .flex-item {
         width: 50px;
         background-color: green;
         margin: 1px;
     }
    
     #item1 {
         align-self: stretch;
     }
    
     #item2 {
         align-self: stretch;
     }
    
     #item3 {
         align-self: stretch;
     }

 

posted @ 2019-11-22 11:01  XYQ全哥  阅读(1761)  评论(0编辑  收藏  举报