flex
布局是 css3 中使用最频繁也是最出色的功能,有点复杂,分为应用在容器上的属性和项目上的属性,即父元素上的与子元素上的属性。
父元素上的属性
- display: flex
<style>
div{display: flex; background-color: yellow;}
b{background-color: red;}
</style>
<body>
<div>
<b>a</b><b>b</b><b>c</b><b>d</b><b>e</b><b>f</b><b>g</b><b>h</b><b>i</b>
</div>
</body>
当父元素设置为 flex
后,其父元素自身会表现成块级元素,如果想表现为行内元素,可以使用 inline-flex
。 所有子元素不管是块级的还是行内的,会立即变成行内布局,这是其他属性的默认值所致的,后面可以修改。
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- flex-direction
<style>
div{display: flex; background-color: yellow; margin: 5px;}
div.row{ flex-direction: row;}
div.row-reverse{ flex-direction: row-reverse;}
div.column{ flex-direction: column;}
div.column-reverse{ flex-direction: column-reverse;}
b{background-color: red;}
</style>
<body>
<div class="row">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="row-reverse">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="column">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="column-reverse">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
</body>
flex-direction
决定子元素的排列方向,默认值 row
。
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- flex-wrap
<style>
div{display: flex; background-color: yellow; margin: 5px; }
div.nowrap{ flex-wrap: nowrap;}
div.wrap{ flex-wrap: wrap;}
div.wrap-reverse{ flex-wrap: wrap-reverse;}
b{background-color: red; width: 100px;}
</style>
<body>
<div class="nowrap">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="wrap">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="wrap-reverse">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
</body>
flex-wrap
决定子元素超出一行时应该如何处理,默认值 nowrap
会压缩子元素的宽度,wrap
是换行,wrap-reverse
则是向上增加新一行。注意:这是在主轴为X轴的前提下讨论的。
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- justify-content
<style>
b{background-color: red; }
div{display: flex; background-color: yellow; margin: 5px; }
div.start{ justify-content: flex-start;}
div.end{justify-content: flex-end;}
div.center{ justify-content: center;}
div.space-between{ justify-content: space-between;}
div.space-around{ justify-content: space-around;}
</style>
<body>
<div class="start">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="end">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="center">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="space-between">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="space-around">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
</body>
justify-content
决定子元素在主轴(当前是X轴)上的位置,默认值 flex-start
。space-between
与 space-around
的间隔是多余空间平分出来的,但后者会为左右端也计入空间。
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- align-items
<style>
b{background-color: red; width: 40px;}
b:nth-child(1){}
b:nth-child(2){font-size: 30px; height: 40px;}
b:nth-child(3){height: 50px;}
b:nth-child(4){height: 60px;}
div{display: flex; flex-wrap: wrap; background-color: yellow; margin: 5px; }
div.start{ align-items: flex-start;}
div.end{ align-items: flex-end;}
div.center{ align-items: center;}
div.baseline{ align-items: baseline;}
div.stretch{ align-items: stretch;}
</style>
<body>
<div class="start">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="end">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="center">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="baseline">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="stretch">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
</body>
align-items
决定副轴(当前为Y轴)上元素的对其方式。默认值 stretch
,表示当子元素不设置高度时,充满父类高度。
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- align-content
<style>
b{background-color: red; width: 100px;}
div{display: flex; flex-wrap: wrap; background-color: yellow; margin: 5px; height: 70px;}
div.start{ align-content: flex-start;}
div.end{ align-content: flex-end;}
div.center{ align-content: center;}
div.space-between{ align-content: space-between;}
div.space-around{ align-content: space-around;}
div.stretch{ align-content: stretch;}
</style>
<body>
<div class="start">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="end">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="center">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="space-between">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="space-around">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
<div class="stretch">
<b>a</b><b>b</b><b>c</b><b>d</b>
</div>
</body>
align-content
表示子元素有多行时,每行在副轴(当前为Y轴)上的位置。默认值 stretch
,表示变动子元素每行的高度,直到充满父元素。
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子元素上的属性
- order
<style>
div{display: flex; background-color: yellow; margin: 5px;}
b{background-color: red; }
b.test{order: -1;}
</style>
<body>
<div class="start">
<b>a</b><b>b</b><b class="test">c</b><b>d</b>
</div>
</body>
order
表示从小到大排列同级元素,默认值 0
。
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- flex-grow
<style>
div{display: flex; background-color: yellow; margin: 5px;}
b{background-color: red; }
b.test{flex-grow: 1; background-color: green;}
</style>
<body>
<div class="start">
<b>a</b><b>b</b><b class="test">c</b><b>d</b>
</div>
</body>
flex-grow
表示当主轴(当前为X轴)上有剩余空间时,平分空间时所占的比例。默认值 0
,表示不占空间。当前空间平分比例为 0 : 0 : 1 : 0
,所以 c 占据所有剩余空间。
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- flex-shrink
<style>
div{display: flex; background-color: yellow; margin: 5px;}
b{background-color: red; width: 100px; flex-shrink: 0;}
b.test{flex-shrink: 1; background-color: green;}
</style>
<body>
<div class="start">
<b>a</b><b>b</b><b class="test">c</b><b>d</b>
</div>
</body>
flex-shrink
表示当主轴(当前为X轴)空间不足以填充所有子元素时,应该如何压缩子元素,默认值 1
,表示 1 : 1 : 1 : 1
,即等比压缩,当前比例为 0 : 0 : 1 : 0
,表示所有空间由 c 来压缩。
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- flex-basis
<style>
div{display: flex; background-color: yellow; margin: 5px;}
b{background-color: red; flex-grow: 1;}
b.test{flex-basis: 100px; background-color: green;}
</style>
<body>
<div class="start">
<b>a</b><b>b</b><b class="test">c</b><b>d</b>
</div>
</body>
flex-basis
表示当主轴(当前为X轴)上平分空间前,先占据的位置,当主轴为X轴,与设置 width
是等效的,当主轴为Y轴,与设置 height
是等效的。默认值 auto
,表示与 width
或 height
相等。
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- align-self
<style>
div{display: flex; background-color: yellow; margin: 5px;}
b{background-color: red; flex-grow: 1;}
b:nth-child(1){height: 20px;}
b:nth-child(2){height: 40px;}
b:nth-child(3){height: 50px;}
b:nth-child(4){height: 60px;}
b.test{align-self: flex-end; background-color: green;}
</style>
<body>
<div class="start">
<b>a</b><b>b</b><b class="test">c</b><b>d</b>
</div>
</body>
align-self
表示当前元素可以覆盖父元素 align-items
所决定的副轴(当前为Y轴)上的方向。默认 auto
,即不设置。可选择与 align-items
一致,auto | flex-start | flex-end | center | baseline | stretch
。
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