前端从零开始（69）flex-direction 排列方向

flex-direction 排列方向

弹性和模型中内部的子元素的排列方向可以通过这个属性修改，那么我们就一起看下它的使用吧。

1. 官方定义

flex-direction 属性规定项目的排列方向。

2. 慕课解释

flex-direction 用来调整主轴的方向，我们知道主轴默认是水平方向且从左到右，而我们可以通过这个属性设置主轴的方向，即项目是水平方向从左到右还是垂直方向从上到下或者从下到上排列。

3. 语法

div{
    flex-direction: row|row-reverse|column|column-reverse|initial|inherit;
}

<div class="demo">
    <div class="item">1</div>
    <div class="item">2</div>
    <div class="item">3</div>
</div>

.demo{
    display:flex; // 让容器变成弹性盒
    flex-direction:row-reverse; 改变项目的排列方向
}

4. 兼容性

IE	Edge	Firefox	Chrome	Safari	Opera	ios	android
10+	12+	28+	4+	6.1+	12.1+	7+	4.4

5. 实例

让子元素从上到下垂直方向排列

.demo{
    display:flex;
    flex-direction:column;
    text-align: center;
    line-height: 100px;
}
.item{
    background:#ccc;
    height:100px;
    border-bottom:1px solid #fff;
}

效果图

从上到下排列效果图

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .demo{
            display:flex;
            flex-direction:column;
            text-align: center;
            line-height: 100px;
        }
        .item{
            background:#ccc;
            height:100px;
            border-bottom:1px solid #fff;
        }
    </style>
</head>
<body>
    <div class="demo">
        <div class="item">1</div>
        <div class="item">2</div>
        <div class="item">3</div>
    </div>
</body>
</html>

让子元素从下到上反向排列

.demo{
    display:flex;
    flex-direction:column-reverse;
    text-align: center;
    line-height: 100px;
}
.item{
    background:#ccc;
    height:100px;
    border-bottom:1px solid #fff;
}

效果图

从上到下反向排列效果图

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .demo{
            display:flex;
            flex-direction:column-reverse;
            text-align: center;
            line-height: 100px;
        }
        .item{
            background:#ccc;
            height:100px;
            border-bottom:1px solid #fff;
        }
    </style>
</head>
<body>
    <div class="demo">
        <div class="item">1</div>
        <div class="item">2</div>
        <div class="item">3</div>
    </div>
</body>
</html>

让子元素从左到右排列

.demo{
    display:flex;
    flex-direction:row;
}
.item{
    background:#ccc;
    height:100px;
    width: 100px;
    border-right:1px solid #fff;
}

效果图

从左到右排列效果图

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .demo{
            display:flex;
            flex-direction:row;
            text-align: center;
            line-height: 100px;
        }
        .item{
            background:#ccc;
            height:100px;
            width: 100px;
            border-right:1px solid #fff;
        }
    </style>
</head>
<body>
    <div class="demo">
        <div class="item">1</div>
        <div class="item">2</div>
        <div class="item">3</div>
    </div>
</body>
</html>

让子元素从左到右反向排列

.demo{
    display:flex;
    flex-direction:row-reverse;
}
.item{
    background:#ccc;
    height:100px;
    width: 100px;
    border-right:1px solid #fff;
}

效果图

从左到右反向排列效果图

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .demo{
            display:flex;
            flex-direction:row-reverse;
            text-align: center;
            line-height: 100px;
        }
        .item{
            background:#ccc;
            height:100px;
            width: 100px;
            border-right:1px solid #fff;
        }
    </style>
</head>
<body>
    <div class="demo">
        <div class="item">1</div>
        <div class="item">2</div>
        <div class="item">3</div>
    </div>
</body>
</html>

6. 经验分享

通过 flex 可以做一个上下固定，中间自适应的布局，它常常用于登录页那类的布局设置。

<div class="demo">
    <div class="head">头部</div>
    <div class="content">内容</div>
    <div class="foot">尾部</div>
</div>

html,body{
    padding:0;
    margin:0;
    height: 100%;
    color:#fff;
}
.demo{
    height: 100%;
    display: flex;
    flex-direction: column;
}
.head,.foot{

    flex:0 1 100px;
    background: #000;
}
.content{
    flex: 1;
    background: red;
}

案例：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>demo</title>
    <style>
    html,body{
        padding:0;
        margin:0;
        height: 100%;
        color:#fff;
    }
    .demo{
        height: 100%;
        display: flex;
        flex-direction: column;
    }
    .head,.foot{

        flex:0 1 100px;
        background: #000;
    }
    .content{
        flex: 1;
        background: red;
    }
    </style>
</head>
<body>
<div class="demo">
    <div class="head">头部</div>
    <div class="content">内容</div>
    <div class="foot">尾部</div>
</div>
</body>
</html>