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Jun 24, 2016 am 11:37 AM

我们经常用伪类来清除浮动，比如这样

.clearfix:after {  content: "";  display: block;  clear: both;  height: 0;}.clearfix {  *zoom: 1; }//hack IE6我们来看一下样例：

<!DOCTYPE html><html><head>    <title></title>    <style>        *{            padding: 0px ;            margin: 0px ;        }        .block{            width: 100px ;            height: 100px ;            float: left ;            margin:10px;            border: solid 1px ;        }        .clearfix:after{            content: "" ;            display: block;            clear: both ;        }    </style></head><body><div class="clearfix">    <div class="block"></div>    <div class="block"></div>    </div>    <div class="block"></div>    <div class="block"></div></body></html>

本来四个格子是同行排列的，清除了浮动后就在清除浮动的地方换行了。

注意一定要是在父类添加清除浮动的clearfix类，如果不加在父类上是没有用的。我个人的理解是这样的，像before和after这样的伪类其实就是在元素内部的前面或后面添加一个元素，这样效果是一样的

<!DOCTYPE html><html><head>    <title></title>    <style>        *{            padding: 0px ;            margin: 0px ;        }        .block{            width: 100px ;            height: 100px ;            float: left ;            margin:10px;            border: solid 1px ;        }        .clear{            clear: both;        }    </style></head><body><div>    <div class="block"></div>    <div class="block"></div>    <div class="clear"></div>    </div>    <div class="block"></div>    <div class="block"></div></body></html>

但注意下面这样是不行的

<body>    <div class="block"></div>    <div class="block clearfix"></div>        <div class="block"></div>    <div class="block"></div></body>

还可以用overflow来清除浮动

<!DOCTYPE html><html><head>    <title></title>    <style>        *{            padding: 0px ;            margin: 0px ;        }        .block{            width: 100px ;            height: 100px ;            float: left ;            margin:10px;            border: solid 1px ;        }        .clear{            overflow: hidden;        }    </style></head><body><div class="clear">    <div class="block"></div>    <div class="block"></div>    </div>    <div class="block"></div>    <div class="block"></div></body></html>

清除浮动的另外一个原因就是要把浮动元素的父元素撑开，为什么用overflow能清除浮动我查到了以下这段话:是因为overflow除了(visible)会重新给他里面的元素建立块级格式化(block formatting context)floats, position absolute, inline-block, table-cell和table-caption都不是块级样式，所以才会用到clear来控制浮动overflow也可以清除浮动是因为当在父级元素设置overflow时候，除了visible，就是只有auto, hidden或者scroll时候，也会建立新的块级格式给他的子元素, 从而起到清楚浮动效果具体信息可以在这里看虽然clear是旧的方式，但还是推荐用clear来做，有些情况会比overflow处理的要好.

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