CSS3 flex布局
2018-10-10 本文已影响4人
Lia代码猪崽
- 布局的传统解决方案，基于盒状模型，依赖 display属性 + position属性 + float属性。
- 它对于那些特殊布局非常不方便，比如，垂直居中就不容易实现。
- 2009年，W3C提出了一种新的方案—-Flex布局，可以简便、完整、响应式地实现各种页面布局。目前，它已经得到了所有浏览器的支持，这意味着，现在就能很安全地使用这项功能。
一、什么是Flex布局
Flex是Flexible Box的缩写，意为”弹性布局”，用来为盒状模型提供最大的灵活性。
任何一个容器都可以指定为Flex布局。
.box{
display: flex;
}
行内元素也可以使用Flex布局。
.box{
display: inline-flex;
}
Webkit内核的浏览器，必须加上-webkit前缀。
.box{
display: -webkit-flex; /* Safari */
display: flex;
}
注意，设为Flex布局以后，子元素的float、clear和vertical-align属性将失效。
二、基本概念
1.容器、项目
采用Flex布局的元素，称为Flex容器（flex container），简称”容器”。它的所有子元素自动成为容器成员，称为Flex项目（flex item），简称”项目”。
2.主轴、交叉轴
容器默认存在两根轴：水平的主轴（main axis）和垂直的交叉轴（cross axis）。
- 主轴的开始位置（与边框的交叉点）叫做main start，结束位置叫做main end；
- 交叉轴的开始位置叫做cross start，结束位置叫做cross end。
- 项目默认沿主轴排列。
- 单个项目占据的主轴空间叫做main size，占据的交叉轴空间叫做cross size。
image.png
三、容器的属性
以下6个属性设置在容器上。
- flex-direction
- flex-wrap
- flex-flow
- justify-content
- align-items
- align-content
以下都沿用这一套代码：
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
width: 48px;
height: 48px;
line-height: 48px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">1</div>
<div class="children">2</div>
<div class="children">3</div>
<div class="children">4</div>
<div class="children">5</div>
<div class="children">6</div>
<div class="children">7</div>
<div class="children">8</div>
<div class="children">9</div>
</div>
</body>
</html>
1.flex-direction属性
flex-direction属性决定主轴的方向（即项目的排列方向），它可能有4个值：
- row（默认值）：主轴为水平方向，起点在左端。
- row-reverse：主轴为水平方向，起点在右端。
- column：主轴为垂直方向，起点在上沿。
- column-reverse：主轴为垂直方向，起点在下沿。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的flex-direction属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
flex-direction: row;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
width: 48px;
height: 48px;
line-height: 48px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">1</div>
<div class="children">2</div>
<div class="children">3</div>
<div class="children">4</div>
<div class="children">5</div>
<div class="children">6</div>
<div class="children">7</div>
<div class="children">8</div>
<div class="children">9</div>
</div>
</body>
</html>
属性值为row
属性值为row-reverse
属性值为column
属性值为column-reverse
2.flex-wrap属性
默认情况下，项目都排在一条线（又称”轴线”）上。
flex-wrap属性定义，如果一条轴线排不下，如何换行，它可能有3个值：
- nowrap（默认）：不换行。
- wrap：换行，第一行在上方。
- wrap-reverse：换行，第一行在下方。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的flex-wrap属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
flex-wrap: wrap ;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
width: 48px;
height: 48px;
line-height: 48px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">1</div>
<div class="children">2</div>
<div class="children">3</div>
<div class="children">4</div>
<div class="children">5</div>
<div class="children">6</div>
<div class="children">7</div>
<div class="children">8</div>
<div class="children">9</div>
<div class="children">10</div>
<div class="children">11</div>
<div class="children">12</div>
<div class="children">13</div>
<div class="children">14</div>
</div>
</body>
属性值为row
属性值为wrap
属性值为wrap-reverse
3.flex-flow
flex-flow属性是flex-direction属性和flex-wrap属性的简写形式，默认值为row nowrap。
4.justify-content
justify-content属性定义了项目在主轴上的对齐方式。
它可能取5个值，具体对齐方式与轴的方向有关。下面假设主轴为从左到右：
- flex-start（默认值）：左对齐
- flex-end：右对齐
- center： 居中
- space-between：两端对齐，项目之间的间隔都相等。
- space-around：每个项目两侧的间隔相等。所以，项目之间的间隔比项目与边框的间隔大一倍。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的justify-content属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
justify-content: flex-start ;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
margin: 10px;
width: 48px;
height: 48px;
line-height: 48px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">1</div>
<div class="children">2</div>
<div class="children">3</div>
<div class="children">4</div>
<div class="children">5</div>
<!--<div class="children">6</div>-->
<!--<div class="children">7</div>-->
<!--<div class="children">8</div>-->
<!--<div class="children">9</div>-->
<!--<div class="children">10</div>-->
<!--<div class="children">11</div>-->
<!--<div class="children">12</div>-->
<!--<div class="children">13</div>-->
<!--<div class="children">14</div>-->
</div>
</body>
</html>
属性值为flex-start
属性值为flex-end
属性值为center
属性值为space-between
属性值为space-around
5.align-items
align-items属性定义项目在交叉轴上如何对齐。
它可能取5个值。具体的对齐方式与交叉轴的方向有关，下面假设交叉轴从上到下：
- flex-start：交叉轴的起点对齐。
- flex-end：交叉轴的终点对齐。
- center：交叉轴的中点对齐。
- baseline: 项目的第一行文字的基线对齐。
- stretch（默认值）：如果项目未设置高度或设为auto，将占满整个容器的高度。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的align-items属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
align-items: flex-start ;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
margin: 10px;
width: 48px;
height: 48px;
line-height: 48px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">1</div>
<div class="children">2</div>
<div class="children">3</div>
<div class="children">4</div>
<div class="children">5</div>
<!--<div class="children">6</div>-->
<!--<div class="children">7</div>-->
<!--<div class="children">8</div>-->
<!--<div class="children">9</div>-->
<!--<div class="children">10</div>-->
<!--<div class="children">11</div>-->
<!--<div class="children">12</div>-->
<!--<div class="children">13</div>-->
<!--<div class="children">14</div>-->
</div>
</body>
</html>
属性值为flex-start
属性值为flex-end
属性值为center
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的align-items属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
align-items: baseline ;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
margin: 10px;
width: 48px;
height: 88px;
line-height: 20px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">
<p>1</p>
<p>2</p>
</div>
<div class="children">2</div>
<div class="children">3</div>
<div class="children">4</div>
<div class="children">5</div>
<!--<div class="children">6</div>-->
<!--<div class="children">7</div>-->
<!--<div class="children">8</div>-->
<!--<div class="children">9</div>-->
<!--<div class="children">10</div>-->
<!--<div class="children">11</div>-->
<!--<div class="children">12</div>-->
<!--<div class="children">13</div>-->
<!--<div class="children">14</div>-->
</div>
</body>
</html>
属性值为baseline
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的flex-direction属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
align-items: stretch;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
margin: 10px;
width: 48px;
/*height: 88px;*/
line-height: 20px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">
<p>1</p>
<p>2</p>
</div>
<div class="children">2</div>
<div class="children">3</div>
<div class="children">4</div>
<div class="children">5</div>
<!--<div class="children">6</div>-->
<!--<div class="children">7</div>-->
<!--<div class="children">8</div>-->
<!--<div class="children">9</div>-->
<!--<div class="children">10</div>-->
<!--<div class="children">11</div>-->
<!--<div class="children">12</div>-->
<!--<div class="children">13</div>-->
<!--<div class="children">14</div>-->
</div>
</body>
</html>
属性值为stretch
6.align-content
align-content属性定义了多根轴线的对齐方式，该属性可能取6个值。
注意：如果项目只有一根轴线，该属性不起作用。所以要搭配flex-direction: row;flex-wrap: wrap;
- stretch（默认值）：轴线占满整个交叉轴。
- flex-start：与交叉轴的起点对齐。
- flex-end：与交叉轴的终点对齐。
- center：与交叉轴的中点对齐。
- space-between：与交叉轴两端对齐，轴线之间的间隔平均分布。
- space-around：每根轴线两侧的间隔都相等。所以，轴线之间的间隔比轴线与边框的间隔大一倍。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的flex-direction属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
flex-wrap: wrap;
align-content: stretch;
align-content: flex-start;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
margin: 5px;
width: 88px;
height: 88px;
line-height: 20px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">
<p>1</p>
<p>2</p>
</div>
<div class="children">2</div>
<div class="children">3</div>
<div class="children">4</div>
<div class="children">5</div>
<div class="children">6</div>
<div class="children">7</div>
<div class="children">8</div>
<div class="children">9</div>
<div class="children">10</div>
<div class="children">11</div>
<div class="children">12</div>
<div class="children">13</div>
<div class="children">14</div>
</div>
</body>
</html>
属性值为stretch
属性值为flex-start
属性值为flex-end
属性值为center
属性值为space-between
属性值为space-around
四、项目的属性
- order
- flex-grow
- flex-shrink
- flex-basis
- flex
- align-self
1.order属性
默认情况下，Flex项目按源顺序排列。
但是，order属性控制它们在Flex容器中的显示顺序。值越小，越靠前。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的order属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
flex-direction: row;
flex-wrap: wrap;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
margin: 5px;
width: 88px;
height: 88px;
line-height: 20px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
.children1 {
order: -1;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">
<p>1</p>
<p>2</p>
</div>
<div class="children children1">2</div>
<div class="children">3</div>
<div class="children children1">4</div>
<div class="children">5</div>
<div class="children children1">6</div>
<div class="children">7</div>
<div class="children children1">8</div>
<div class="children">9</div>
<div class="children children1">10</div>
<div class="children">11</div>
<div class="children children1">12</div>
<div class="children">13</div>
<div class="children children1">14</div>
</div>
</body>
</html>
加了children1类的模块顺序在前面了
2.flex-grow
- flex-grow属性定义项目的放大比例，默认为0，即如果存在剩余空间，也不放大。
- 如果所有项目的flex-grow属性都为1，则它们将等分剩余空间（如果有的话）。
- 如果一个项目的flex-grow属性为2，其他项目都为1，则前者占据的剩余空间将比其他项多一倍。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的flex-grow属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
flex-direction: row;
flex-wrap: wrap;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
margin: 5px;
width: 88px;
height: 88px;
line-height: 20px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
.children1 {
flex-grow: 1;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">
<p>1</p>
<p>2</p>
</div>
<div class="children children1">2</div>
<div class="children">3</div>
<div class="children children1">4</div>
<div class="children">5</div>
<div class="children children1">6</div>
<div class="children">7</div>
<div class="children children1">8</div>
<div class="children">9</div>
<div class="children children1">10</div>
<div class="children">11</div>
<div class="children children1">12</div>
<div class="children">13</div>
<div class="children children1">14</div>
</div>
</body>
</html>
只有有足够空间的最后一行加了children1的模块放大了一倍
3.flex-shrink
- flex-shrink属性定义了项目的缩小比例，默认为1，即如果空间不足，该项目将缩小。
- 如果所有项目的flex-shrink属性都为1，当空间不足时，都将等比例缩小。
- 如果一个项目的flex-shrink属性为0，其他项目都为1，则空间不足时，前者不缩小。
- 负值对该属性无效。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的flex-shrink属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
flex-direction: row;
/*flex-wrap: wrap;*/
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
margin: 5px;
width: 88px;
height: 88px;
line-height: 20px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
.children1 {
flex-shrink: 0;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">
<p>1</p>
<p>2</p>
</div>
<div class="children children1">2</div>
<div class="children">3</div>
<div class="children children1">4</div>
<div class="children">5</div>
<div class="children children1">6</div>
<div class="children">7</div>
<div class="children children1">8</div>
<div class="children">9</div>
<div class="children children1">10</div>
<div class="children">11</div>
<div class="children children1">12</div>
<div class="children">13</div>
<div class="children children1">14</div>
</div>
</body>
</html>
添加了children1的模块都没有缩小
4.flex-basis
- flex-basis属性定义了在分配多余空间之前，项目占据的主轴空间（main size）。
- 浏览器根据这个属性，计算主轴是否有多余空间。它的默认值为auto，即项目的本来大小。
- 它可以设为跟width或height属性一样的值（比如350px），则项目将占据固定空间。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的flex-basis属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
flex-direction: row;
flex-wrap: wrap;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
margin: 5px;
width: 88px;
height: 88px;
line-height: 20px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
.children1 {
flex-basis: 60px;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">
<p>1</p>
<p>2</p>
</div>
<div class="children children1">2</div>
<div class="children">3</div>
<div class="children children1">4</div>
<div class="children">5</div>
<div class="children children1">6</div>
<div class="children">7</div>
<div class="children children1">8</div>
<div class="children">9</div>
<div class="children children1">10</div>
<div class="children">11</div>
<div class="children children1">12</div>
<div class="children">13</div>
<div class="children children1">14</div>
</div>
</body>
</html>
模块宽度变为60px
5.flex
- flex属性是flex-grow, flex-shrink 和 flex-basis的简写，默认值为0 1 auto。后两个属性可选。
- 该属性有两个快捷值：auto (1 1 auto) 和 none (0 0 auto)。
- 建议优先使用这个属性，而不是单独写三个分离的属性，因为浏览器会推算相关值。
6.align-self
- align-self属性允许单个项目有与其他项目不一样的对齐方式，可覆盖align-items属性。
- 默认值为auto，表示继承父元素的align-items属性，如果没有父元素，则等同于stretch。
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Flex布局的align-self属性</title>
<style>
body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.parent {
display: flex;
flex-direction: row;
flex-wrap: wrap;
width: 500px;
height: 500px;
background-color: palevioletred;
}
.children {
margin: 5px;
width: 88px;
height: 88px;
line-height: 20px;
text-align: center;
color: #fff;
background-color: rebeccapurple;
border: 1px solid red;
}
.children1 {
align-self: flex-end;
}
</style>
</head>
<body>
<div class="parent">
<div class="children">
<p>1</p>
<p>2</p>
</div>
<div class="children children1">2</div>
<div class="children">3</div>
<div class="children children1">4</div>
<div class="children">5</div>
<div class="children children1">6</div>
<div class="children">7</div>
<div class="children children1">8</div>
<div class="children">9</div>
<div class="children children1">10</div>
<div class="children">11</div>
<div class="children children1">12</div>
<div class="children">13</div>
<div class="children children1">14</div>
</div>
</body>
</html>
加了children1类的模块对齐方式发生改变
参考资料
https://css-tricks.com/snippets/css/a-guide-to-flexbox/
https://www.runoob.com/w3cnote/flex-grammar.html
