CSS实现等高布局

等高布局是指子元素在父元素中高度相等的布局方式。等高布局的实现包括伪等高和真等高，伪等高只是看上去等高而已，真等高是实实在在的等高。本文将介绍边框模拟、负margin这两种伪等高以及table实现、absolute实现、flex实现、grid实现和js判断这五种真等高布局

1.边框模拟(伪等高)

因为元素边框和元素高度始终是相同高度，用元素的边框颜色来伪装左右两个兄弟元素的背景色。然后将左右两个透明背景的元素使用absolute覆盖在中间元素的左右边框上，实现视觉上的等高效果

[注意]左右两侧元素的内容高度不能大于中间元素内容高度，否则无法撑开容器高度

<style>
body,p{margin: 0;}
.parent{
    position: relative;
}
.center{
    box-sizing:border-box;
    padding: 0 20px;
    background-clip: content-box;
    border-left: 210px solid lightblue;
    border-right: 310px solid lightgreen;
}
.left{
    position: absolute;
    top: 0;
    left: 0;
    width: 200px;
}
.right{
    position: absolute;
    top: 0;
    right: 0;
    width: 300px;
}
</style>

<div class="parent" style="background-color: lightgrey;">
    <div class="left">
        <p>left</p>
    </div>  
    <div class="center" style="background-color: pink;">
        <p>center</p>
        <p>center</p>
    </div>          
    <div class="right">
        <p>right</p>
    </div>        
</div>

2。负margin(伪等高)

　　因为背景是在padding区域显示的，设置一个大数值的padding-bottom，再设置相同数值的负的margin-bottom，使背景色铺满元素区域，又符合元素的盒模型的计算公式，实现视觉上的等高效果

　　[注意]如果页面中使用<a>锚点跳转时，将会隐藏部分文字信息

　　[注意]如果页面中的背景图片定位到底部，将会看不到背景图片

<style>
body,p{margin: 0;}
.parent{
    overflow: hidden;
}
.left,.centerWrap,.right{
    float: left;
    width: 50%;
    padding-bottom: 9999px;
    margin-bottom: -9999px;
}
.center{
    margin: 0 20px;
}
.left,.right{
    width: 25%;
}
</style>

<div class="parent" style="background-color: lightgrey;">
    <div class="left" style="background-color: lightblue;">
        <p>left</p>
    </div>  
    <div class="centerWrap">
        <div class="center" style="background-color: pink;">
            <p>center</p>
            <p>center</p>
        </div>         
    </div>
         
    <div class="right" style="background-color: lightgreen;">
        <p>right</p>
    </div>        
</div>

3.table(真等高)

table元素中的table-cell元素默认就是等高的

  <style>
    body,
    p {
      margin: 0;
    }
    .parent {
      display: table;
      width: 100%;
      table-layout: fixed;
    }
    .left,
    .centerWrap,
    .right {
      display: table-cell;
    }
    .center {
      margin: 0 20px;
    }
  </style>

  <div class="parent" style="background-color: lightgrey;">
    <div class="left" style="background-color: lightblue;">
      <p>left</p>
    </div>
    <div class="centerWrap">
      <div class="center" style="background-color: pink;">
        <p>center</p>
        <p>center</p>
      </div>
    </div>
    <div class="right" style="background-color: lightgreen;">
      <p>right</p>
    </div>
  </div>

4.absolute(真等高)

设置子元素的top:0;bottom:0;使得所有子元素的高度都和父元素的高度相同，实现等高效果

<style>
body,p{margin: 0;}
.parent{
    position: relative;
    height: 40px;
}
.left,.center,.right{
    position: absolute;
    top: 0;
    bottom: 0;
}
.left{
    left: 0;
    width: 100px;
}
.center{
    left: 120px;
    right: 120px;
}
.right{
    width: 100px;
    right: 0;
}
</style>

<div class="parent" style="background-color: lightgrey;">
    <div class="left" style="background-color: lightblue;">
        <p>left</p>
    </div>  
    <div class="center" style="background-color: pink;">
        <p>center</p>
        <p>center</p>
    </div>          
    <div class="right" style="background-color: lightgreen;">
        <p>right</p>
    </div>        
</div>

5.flex(真等高)

flex中的伸缩项目默认都拉伸为父元素的高度，也实现了等高效果

<style>
body,p{margin: 0;}
.parent{
    display: flex;
}
.left,.center,.right{
    flex: 1;
}
.center{
    margin: 0 20px;
}
</style>

<div class="parent" style="background-color: lightgrey;">
    <div class="left" style="background-color: lightblue;">
        <p>left</p>
    </div>  
    <div class="center" style="background-color: pink;">
        <p>center</p>
        <p>center</p>
    </div>          
    <div class="right" style="background-color: lightgreen;">
        <p>right</p>
    </div>        
</div>

 6.grid(真等高)

<style>
body,p{margin: 0;}
.parent{
    display: grid;
    grid-auto-flow: column;
    grid-gap:20px;
}
</style>

<div class="parent" style="background-color: lightgrey;">
    <div class="left" style="background-color: lightblue;">
        <p>left</p>
    </div>  
    <div class="center" style="background-color: pink;">
        <p>center</p>
        <p>center</p>
    </div>          
    <div class="right" style="background-color: lightgreen;">
        <p>right</p>
    </div>        
</div>

7.js(真等高)

当子元素高度不同时，进行js判断，增加较低子元素的padding-bottom，使得各个子元素实现等高效果

<style>
body,p{margin: 0;}
.parent{overflow: hidden;}
.left,.center,.right{
    float: left;
    width: 25%;
}    
.center{
    width: 50%;
    padding: 0 20px;
    background-clip: content-box;
    box-sizing: border-box;
}
</style>

<div class="parent" id="parent" style="background-color: lightgrey;">
    <div class="left" style="background-color: lightblue;">
        <p>left</p>
    </div>  
    <div class="center" style="background-color: pink;">
        <p>center</p>
        <p>center</p>
    </div>          
    <div class="right" style="background-color: lightgreen;">
        <p>right</p>
    </div>        
</div>

<script>
function getCSS(obj,style){
    if(window.getComputedStyle){
        return getComputedStyle(obj)[style];
    }
    return obj.currentStyle[style];
}
var oParent = document.getElementById('parent');
var oLeft = oParent.getElementsByTagName('div')[0];
var oCenter = oParent.getElementsByTagName('div')[1];
var oRight = oParent.getElementsByTagName('div')[2];
function eqHeight(obj1,obj2){
    var oDis = obj1.clientHeight - obj2.clientHeight;
    if(oDis > 0){
        obj2.style.paddingBottom = parseFloat(getCSS(obj2,'padding-bottom')) + oDis + 'px';
    }else{
        obj1.style.paddingBottom = parseFloat(getCSS(obj1,'padding-bottom')) +  Math.abs(oDis) + 'px';
    }
}
eqHeight(oLeft,oCenter);
eqHeight(oLeft,oRight);
</script>

转载于https://www.cnblogs.com/xiaohuochai/p/5457127.html