flex布局学习笔记

最近学习跳槽面试,发现学习知识总是会遗忘的。不如总结记录下来,方便回忆。

flex布局定义

flex布局又叫弹性布局,伸缩布局,通过给父容器设置dispaly:flex属性,子元素实现弹性布局。父容器实现弹性布局后,子元素的一些属性也会消失,如子元素的float,clear,vertical-align属性

(学习前要了解,flex布局有主轴和副轴的概念,默认横向为主轴,纵向为副轴。)

设置flex  display:flex

设置父元素display:flex后,子元素沿主轴排列

<style>
    div {
        display: flex;
        background-color: pink;
        width: 400px;
        height: 400px;
    }
    div span {
        background-color: red;
        margin: 5px 5px;
        width:50px;
        height: 50px;
    }
</style>
<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
    </div>
</body>

设置主轴方向  flex-direction

flex-direction:row(colum)

row:横向排列 row-reverse:横向反向排列(从右至左)

colum:纵向排列 colum-reverse:纵向排列(从下至上)设置主轴方向

<style>
    div {
        display: flex;
        /* flex父元素属性设置 1.flex-direction 设置主轴方向 排列方式,默认为row横向排列 */
        /*  */
        flex-direction: row;
        /* flex-direction: row-reverse;
        flex-direction: column;
        flex-direction:colum-reverse; */
        background-color: pink;
        width: 400px;
        height: 400px;
    }
    div span {
        background-color: red;
        margin: 5px 5px;
        width:50px;
        height: 50px;
    }
</style>
<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
    </div>
</body>

设置主轴排列方式  justify-content

justify-content:flex-start|flex-end|center|space-around|space-between

 当主轴是row时,代码效果如下

justify-content:flex-start

<style>
    div {
        display: flex;
        /* flex父元素属性设置 1.flex-direction 设置主轴方向 排列方式,默认为row横向排列 */
        /*  */
        flex-direction: row;
        /* flex-direction: row-reverse;
        flex-direction: column;
        flex-direction:colum-reverse; */
        justify-content: flex-start;
        /* justify-content: flex-end; */
        /* justify-content: center;
        justify-content: space-around;
        justify-content: space-between; */
        background-color: pink;
        width: 400px;
        height: 400px;
    }
    div span {
        background-color: red;
        margin: 5px 5px;
        width:50px;
        height: 50px;
    }
</style>
<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
    </div>
</body>

效果如下 

 

justify-content:flex-end

 

 justify-content:center 

 

 justify-content:space-around

 justify-content:space-between

两端对齐后居中

设置副轴排列方式  align-item

align-item(单行) align-content(副轴换行时对齐方式)

设置换行  flex-wrap

flex-wrap:no-wrap|wrap(默认不换行)

如下图,当子元素宽度总和超过父容器宽度时,子元素宽度会沿着父容器方向被压缩。不足100px

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    div {
        display: flex;
        /* flex父元素属性设置 1.flex-direction 设置主轴方向 排列方式,默认为row横向排列 */
        /*  */
        flex-direction: row;
        /* flex-direction: row-reverse;
        flex-direction: column;
        flex-direction:colum-reverse; */
        justify-content: flex-start;
        /* justify-content: flex-end; */
         /* justify-content: center; */
        /* justify-content: space-around; */
        /* justify-content: space-between;  */
        background-color: pink;
        width: 400px;
        height: 400px;
    }
    div span {
        background-color: red;
        margin: 5px 5px;
        height: 50px;
        width: 100px;
    }
</style>
<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
        <span>4</span>
        <span>5</span>
        <span>6</span>
    </div>
</body>
</html>

设置flex-wrap:wrap后效果

 

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    div {
        display: flex;
        /* flex父元素属性设置 1.flex-direction 设置主轴方向 排列方式,默认为row横向排列 */
        /*  */
        flex-direction: row;
        /* flex-direction: row-reverse;
        flex-direction: column;
        flex-direction:colum-reverse; */
        justify-content: flex-start;
        /* justify-content: flex-end; */
         /* justify-content: center; */
        /* justify-content: space-around; */
        /* justify-content: space-between;  */
        background-color: pink;
        width: 400px;
        height: 400px;
        flex-wrap:wrap
    }
    div span {
        background-color: red;
        margin: 5px 5px;
        height: 50px;
        width: 100px;
    }
</style>
<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
        <span>4</span>
        <span>5</span>
        <span>6</span>
    </div>
</body>
</html>

 

flex-flow属性

flex-flow是flex-direction属性和flex-warp的组合写法。如flex-flow:row warp;即可实现行排列和换行操作。

子元素属性

flex属性

设置子盒子占用父盒子剩余空间比例.

如下图,设置父盒子宽度为80%,设置1 3 子容器宽度固定,给子元素2设置flex:1属性后。即可分配父盒子剩余空间,且会因为屏幕大小变化而自适应。

<!-- 设置主轴上元素排列方式 -->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    /* 元素跟着主轴走 */
    /* flex父元素属性设置 1.flex-direction 设置主轴方向 排列方式 */
    div {
        display: flex;
        /* 设置主轴方向,竖向排列,竖向相反排列 */
        flex-direction: row;
        /* flex-direction: column; */
        /* flex-direction: column-reverse;
        flex-direction: row;
        flex-direction: row-reverse; */
        /* justify-content: center; */
        /* justify-content: flex-end; */
        /* justify-content: left; */
        /* justify-content: space-around; */
        justify-content: space-between;
        align-items: center;
        align-content: space-between;
        /* align-items: stretch; */
        /* 是否自动换行 */
        flex-wrap: wrap;  

        background-color: pink;
        width: 80%;
        height: 400px;
    }
    div span:nth-child(1) {
        background-color: red;
        /* flex: 1; */
        margin: 5px 5px;
        height: 50px;
        width: 50px;
    }
    div span:nth-child(2) {
        background-color: red;
        flex: 1;
    }
    div span:nth-child(3) {
        background-color: red;
        /* flex: 1; */
        margin: 5px 5px;
        height: 50px;
        width: 50px;
    }
</style>
<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
    </div>
</body>
</html>

当不设置子元素宽度,设置flex:1时,即可实现子元素平均分配父元素空间操作。

<!-- 设置主轴上元素排列方式 -->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    /* 元素跟着主轴走 */
    /* flex父元素属性设置 1.flex-direction 设置主轴方向 排列方式 */
    div {
        display: flex;
        flex-direction: row;
        align-items: center;
        flex-wrap: wrap;  
        background-color: pink;
        width: 80%;
        height: 400px;
    }
    div span{
        background-color: red;
        flex: 1;
        height: 100px;
        border: 1px solid beige;
    }
    
</style>
<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
    </div>
</body>
</html>

效果如下:

 

align-self属性

设置子元素本身侧轴排列方式

<!-- 设置主轴上元素排列方式 -->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    /* 元素跟着主轴走 */
    /* flex父元素属性设置 1.flex-direction 设置主轴方向 排列方式 */
    div {
        display: flex;
        flex-direction: row;
        align-items: center;
        flex-wrap: wrap;  
        background-color: pink;
        width: 80%;
        height: 400px;
    }
    div span{
        background-color: red;
        flex: 1;
        height: 100px;
        border: 1px solid beige;
    }
    div span:nth-child(3){
        align-self: flex-end;
    }
    
</style>
<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
    </div>
</body>
</html>

效果如下:

order属性 

设置子元素顺序,数值越小,越靠前,默认为0;

<!-- 设置主轴上元素排列方式 -->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    /* 元素跟着主轴走 */
    /* flex父元素属性设置 1.flex-direction 设置主轴方向 排列方式 */
    div {
        display: flex;
        flex-direction: row;
        align-items: center;
        flex-wrap: wrap;  
        background-color: pink;
        width: 80%;
        height: 400px;
    }
    div span{
        background-color: red;
        flex: 1;
        height: 100px;
        border: 1px solid beige;
    }
    div span:nth-child(2){
        align-self: flex-start;
        order: -1;
    }
    div span:nth-child(3){
        align-self: flex-end;
    }
    
</style>
<body>
    <div>
        <span>1</span>
        <span>2</span>
        <span>3</span>
    </div>
</body>
</html>

效果如下:

总结

以上就是本次学习过程中常用的flex布局属性,后续会补充。

学习链接:【黑马!真的很详细!】CSS3-flex布局(flex布局的单个知识点忘记也可以复习)_哔哩哔哩_bilibili

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