255 lines
5.1 KiB
Markdown
255 lines
5.1 KiB
Markdown
# 浮动（float）
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## 为什么需要浮动
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- 最初浮动是为了像word有文字环绕，图片嵌入的功能出现的
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- 让多个块级元素水平排列成一行
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- 实现两个块级盒子的左对齐和右对齐
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## 浮动的本质
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1. 浮动的包裹性
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抛开浮动的破坏性先不谈，浮动就是个带有方位的display:inline-block的属性。
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display:inline-block 某种意义上的作用就是包裹，浮动也有类似的效果
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但是 float和display:inline-block 无法完全等同
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原因：
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- float可以自定义方向（从左往右或从右往左） inline-block只有从左到右一个水平排列的方向
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- float会使周围文字环绕元素 inline-block不会
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2. 浮动的破坏性
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flex破坏性指的是，父元素高度塌陷 。
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把一张图片放在div里显示：
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```
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<div class="outer">
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<img src="./images/2.jpg" width="150px" height="100px">x
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</div>
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```
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```
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.outer{
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width: 400px;
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background-color: lightblue;
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}
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```
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这时候如果给图片加上float:left ,父元素蓝色框就只有x占据的宽度
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```
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.outer{
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width: 400px;
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background-color: lightblue;
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float:left;
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}
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```
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这时候如果把x去掉 那么父元素（蓝色框） 就直接没了
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## float 使用
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```
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float:left 左浮动
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float:right 右浮动
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```
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float:left 实现块级元素水平排列
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```
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>Document</title>
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<style>
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*{
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margin:0;
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padding: 0;
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}
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.box{
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width: 1000px;
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height: 300px;
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background: gold;
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margin: 20px;
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}
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.box1{
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/* width:60px;
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height: 60px; */
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background: red;
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/* background: rgba(255, 0, 0, 0.363); */
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/* float: left; */
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}
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.box2{
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width: 120px;
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height:80px;
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background: gray;
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border: 1px solid pink;
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/* float:right */
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float: left;
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}
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.a{
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/* width: 70px;
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height: 70px;
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border: 1px solid blue;
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background: pink; */
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clear: right;
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}
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</style>
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</head>
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<body>
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<div class="box">
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<div class="box1">asaaaa</div>
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<div class="box2"></div>
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<div class="box2"></div>
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<div class="box2"></div>
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<div class="box2"></div>
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<div class="box2"></div>
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<div class="box2"></div>
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</div>
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</body>
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</html>
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```
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## 清除浮动
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```
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clear:left(清除左浮动)/right(清除右浮动)/both(清除左浮动+右浮动)
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```
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哪边不允许有浮动元素，clear就是对应方向的值，两边都不允许就是`both`
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方案1：给需要清浮动的元素加clear属性
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```
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.box4{
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width: 120px;
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height:80px;
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background: blue;
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border: 1px solid pink;
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clear: left;
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}
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```
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方案2：
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html:
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```
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<div class="box">
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<div class="box1">asaaaa</div>
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<div class="box2"></div>
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<div class="box2">4</div>
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<div class="box2">5</div>
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<!-- <div class="box2" style="height: 180px;">6</div> -->
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<div class="blank"></div>
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<div class="box4"></div>
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</div>
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```
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css:
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```
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.blank{
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clear: left;
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}
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```
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方案3：使用伪元素清除浮动
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css:
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```
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.boxes:after {
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content: '.';
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height: 0;
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display: block;
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clear: both;
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}
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```
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html:
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```
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<div class="box">
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<div class="boxes clearfix">
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<div class="box1">asaaaa</div>
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<div class="box2"></div>
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<div class="box2">4</div>
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<div class="box2 blankdiv">5</div>
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<!-- <div class="box2" style="height: 180px;">6</div> -->
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<div class="blank"></div>
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</div>
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<div class="box4"></div>
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</div>
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```
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方案4：overflow 清除浮动
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html：
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```
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<div class="box">
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<div class="boxes clearfix">
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<div class="box1">asaaaa</div>
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<div class="box2"></div>
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<div class="box2">4</div>
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<div class="box2 blankdiv">5</div>
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<!-- <div class="box2" style="height: 180px;">6</div> -->
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<div class="blank"></div>
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</div>
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<div class="box4"></div>
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</div>
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```
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css:
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```
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.boxes{
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overflow: auto;
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}
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```
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