浅谈flex布局

读阮大神的文章整理，原文请移步。

学习小建议：flex布局在实战之前，需要了解相关属性，在进行实战的训练，你会感觉到倍爽。

传统的布局基于盒子模型，依赖display属性和position属性和float属性，它在实现一些布局的时候非常的不方便，如垂直居中。

1.flex布局是弹性布局的意思，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；
}

行内元素也可使用：

.box{
	display:inline-flex;
}

2.采用flex布局，称flex为容器，它的所有子元素自动成为容器成员。

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。

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

3.容器的属性

  • flex-direction
  • flex-wrap
  • flex-flow
  • justify-content
  • align-items
  • align-content

3.1flex-direction属性决定主轴的方向，即项目的排列放方向。

.box {
  flex-direction: row | row-reverse | column | column-reverse;
}
  • 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。

3.2flex-wrap属性，flex容器中的元素是否按照轴线排列。

.box{
  flex-wrap: nowrap | wrap | wrap-reverse;
}
  • 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。

3.3 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

.box {
  flex-flow: <flex-direction> || <flex-wrap>;
}

3.4 justify-content属性定义了项目在主轴上的对齐方式。

.box {
  justify-content: flex-start | flex-end | center | space-between | space-around;
}
  • 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。

3.5 align-items属性定义项目在交叉轴上如何对齐。

.box {
  align-items: flex-start | flex-end | center | baseline | stretch;
}
  • 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。

3.6 align-content属性定义了多根轴线的对齐方式。如果项目只有一根轴线，该属性不起作用。

.box {
  align-content: flex-start | flex-end | center | space-between | space-around | stretch;
}
  • 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。
  • stretch（默认值）：轴线占满整个交叉轴。

项目实战： 一个子元素##

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>flex</title>
    <style type="text/css">
        .box{
            width: 100px;
            height: 100px;
            background: gainsboro;
            margin: 50px auto;
            border-radius: 20px;
        }


        .item{
            width: 20px;
            height: 20px;
            background: black;
            border-radius: 10px;
            margin: 5px 5px;
        }



        .box{
            display: flex;  /*左上角默认首行左对齐*/
        }

        .box{
            display: flex;
            justify-content: center;  /*设置元素的对齐方式*/
        }

        .box{
            display: flex;
            justify-content: flex-end;
        }


        .box{
            display: flex;
            align-items: center;  /*设置主轴对齐方式*/
        }

        .box{
            display: flex;
            justify-content: center;
            align-items: center;
        }


        .box{
            display: flex;
            justify-content: center;
            align-items: flex-end;
        }

        .box{
            display: flex;
            justify-content: flex-end;
            align-items: flex-end;
        }
    </style>
</head>
<body>
<div class="box">
    <span class="item"></span>
</div>
</body>
</html>

项目实战：两个子元素

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>flex</title>
    <style type="text/css">
        .box{
            width: 100px;
            height: 100px;
            background: gainsboro;
            margin: 50px auto;
            border-radius: 20px;
        }


        .item{
            width: 20px;
            height: 20px;
            background: black;
            border-radius: 10px;
            margin: 10px 10px;
        }

        .box{
            display: flex;
            justify-content: space-between;
        }

        .box{
            display: flex;
            flex-direction: column;
            justify-content: space-between;
        }

        .box{
            display: flex;
            flex-direction: column;
            justify-content: space-between;
            align-items: center;
        }

        .box{
            display: flex;
            flex-direction: column;
            justify-content: space-between;
            align-items: flex-end;
        }

        .box{
            display: flex;
        }

        .item:nth-child(2){
            align-self: center;
        }


        .box{
            display: flex;
            justify-content: space-between;
        }
        .item:nth-child(2){
            align-self: flex-end;
        }
    </style>
</head>
<body>
<div class="box">
    <span class="item"></span>
    <span class="item"></span>
</div>
</body>
</html>

项目实战：三个子元素

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>flex</title>
    <style type="text/css">
        .box{
            width: 100px;
            height: 100px;
            background: gainsboro;
            margin: 50px auto;
            border-radius: 20px;
        }


        .item{
            width: 10px;
            height: 10px;
            background: black;
            border-radius: 10px;
            margin: 10px 10px;
        }

        .box{
            display: flex;
        }

        .item:nth-child(2){
            align-self: center;
        }
        .item:nth-child(3){
            align-self: flex-end;
        }

    </style>
</head>
<body>
<div class="box">
    <span class="item"></span>
    <span class="item"></span>
    <span class="item"></span>
</div>
</body>
</html>

项目实战：四个子元素

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>flex</title>
    <style type="text/css">
        .box{
            width: 100px;
            height: 100px;
            background: gainsboro;
            margin: 50px auto;
            border-radius: 20px;
        }


        .item{
            width: 20px;
            height: 20px;
            background: black;
            border-radius: 10px;
            margin: 5px 5px;
        }

        .box{
            display: flex;
            flex-wrap: wrap;
            justify-content: flex-end;
            align-content: space-between;
        }

    </style>
</head>
<body>
<div class="box">
    <span class="item"></span>
    <span class="item"></span>
    <span class="item"></span>
    <span class="item"></span>
</div>
</body>
</html>


<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>flex</title>
    <style type="text/css">
        .box{
            width: 100px;
            height: 100px;
            background: gainsboro;
            margin: 50px auto;
            border-radius: 20px;
            display: flex;
            flex-wrap: wrap;
            align-content: space-between;
        }

        .column {
            flex-basis: 100%;
            display: flex;
            justify-content: space-between;
        }


        .item{
            width: 20px;
            height: 20px;
            background: black;
            border-radius: 10px;
            margin: 5px 5px;
        }

    </style>
</head>
<body>
<div class="box">
    <div class="column">
        <span class="item"></span>
        <span class="item"></span>
    </div>
    <div class="column">
        <span class="item"></span>
        <span class="item"></span>
    </div>
</div>
</body>
</html>

项目是实战：六个子元素

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>flex</title>
    <style type="text/css">
        .box{
            width: 100px;
            height: 100px;
            background: gainsboro;
            margin: 50px auto;
            border-radius: 20px;
            display: flex;
            flex-wrap: wrap;
        }

        .row{
            flex-basis: 100%;
            display:flex;
        }

        .row:nth-child(2){
            justify-content: center;
        }

        .row:nth-child(3){
            justify-content: space-between;
        }


        .item{
            width: 20px;
            height: 20px;
            background: black;
            border-radius: 10px;
            margin: 5px 5px;
        }

    </style>
</head>
<body>
<div class="box">
    <div class="row">
        <span class="item"></span>
        <span class="item"></span>
        <span class="item"></span>
    </div>
    <div class="row">
        <span class="item"></span>
    </div>
    <div class="row">
        <span class="item"></span>
        <span class="item"></span>
    </div>
</div>
</body>
</html>

实战布局：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>流式布局</title>
    <style type="text/css">
        .parent{
            width: 200px;
            height: 150px;
            background: black;
            display: flex;
            flex-flow: row wrap;
            align-content: flex-start;
        }

        .child{
            box-sizing: border-box;
            background-color: white;
            flex: 0 0 25%;
            height: 50px;
            border:  1px solid rebeccapurple;
        }
    </style>
</head>
<body>
<div class="parent">
    <div class="child"></div>
    <div class="child"></div>
    <div class="child"></div>
    <div class="child"></div>
    <div class="child"></div>
    <div class="child"></div>
    <div class="child"></div>
    <div class="child"></div>
    <div class="child"></div>
</div>
</body>
</html>

最后来一道大菜：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>flex</title>
    <style type="text/css">
        .first-face {
            display: flex;
            justify-content: center;
            align-items: center;
        }

        .second-face {
            display: flex;
            justify-content: space-between;
        }

        .second-face .pip:nth-of-type(2) {
            align-self: flex-end;
        }

        .third-face {
            display: flex;
            justify-content: space-between;
        }

        .third-face .pip:nth-of-type(2) {
            align-self: center;
        }

        .third-face .pip:nth-of-type(3) {
            align-self: flex-end;
        }

        .fourth-face, .sixth-face {
            display: flex;
            justify-content: space-between;
        }

        .fourth-face .column, .sixth-face .column {
            display: flex;
            flex-direction: column;
            justify-content: space-between;
        }

        .fifth-face {
            display: flex;
            justify-content: space-between;
        }

        .fifth-face .column {
            display: flex;
            flex-direction: column;
            justify-content: space-between;
        }

        .fifth-face .column:nth-of-type(2) {
            justify-content: center;
        }

        /* OTHER STYLES */

        * {
            box-sizing: border-box;
        }

        html, body {
            height: 100%;
        }

        body {
            display: flex;
            align-items: center;
            justify-content: center;
            vertical-align: center;
            flex-wrap: wrap;
            align-content: center;
            font-family: 'Open Sans', sans-serif;

            background: linear-gradient(top, #222, #333);
        }

        [class$="face"] {
            margin: 16px;
            padding: 4px;

            background-color: #e7e7e7;
            width: 104px;
            height: 104px;
            object-fit: contain;

            box-shadow:
                    inset 0 5px white,
                    inset 0 -5px #bbb,
                    inset 5px 0 #d7d7d7,
                    inset -5px 0 #d7d7d7;

            border-radius: 10%;
        }

        .pip {
            display: block;
            width: 24px;
            height: 24px;
            border-radius: 50%;
            margin: 4px;

            background-color: #333;
            box-shadow: inset 0 3px #111, inset 0 -3px #555;
        }
    </style>
</head>
<body>
    <div class="first-face">
        <span class="pip"></span>
    </div>
    <div class="second-face">
        <span class="pip"></span>
        <span class="pip"></span>
    </div>
    <div class="third-face">
        <span class="pip"></span>
        <span class="pip"></span>
        <span class="pip"></span>
    </div>
    <div class="fourth-face">
        <div class="column">
            <span class="pip"></span>
            <span class="pip"></span>
        </div>
        <div class="column">
            <span class="pip"></span>
            <span class="pip"></span>
        </div>
    </div>
    <div class="fifth-face">
        <div class="column">
            <span class="pip"></span>
            <span class="pip"></span>
        </div>
        <div class="column">
            <span class="pip"></span>
        </div>
        <div class="column">
            <span class="pip"></span>
            <span class="pip"></span>
        </div>
    </div>
    <div class="sixth-face">
        <div class="column">
            <span class="pip"></span>
            <span class="pip"></span>
            <span class="pip"></span>
        </div>
        <div class="column">
            <span class="pip"></span>
            <span class="pip"></span>
            <span class="pip"></span>
        </div>
    </div>
</body>
</html>

粘贴到你的编辑器里面即可看到效果。