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About the flexible layout of css flex

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Release: 2018-06-14 17:05:24
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This article mainly introduces relevant information on the detailed explanation of css flex elastic layout. The editor thinks it is quite good, so I will share it with you now and give it as a reference. Let’s follow the editor to take a look

Basic layout of the case

html

    <ul class="box">
        <li class="item"></li>
        <li class="item"></li>
        <li class="item"></li>
        <li class="item"></li>
    </ul>
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css

        .box{
            display: -webkit-flex;
            display: flex;
        }
        .item{
            width: 200px;
            height: 300px;
            background: red;
            border: 1px solid #ccc;
            font-size: 50px;
            text-align: center;
            line-height: 300px;
            color:#fff;
        }
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Because flex is mainly convenient and Mobile layout, so the test uses Google to simulate the mobile side to see the effect:

Because flex layout is used, the sub-elements are arranged horizontally by default, so float is not required and will not work. ;

Exploration of parent box properties

flex-direction

flex-direction represents child elements The arrangement direction and order; default row (horizontal, left to right); row-reverse means horizontal right to left

.box{
            display: -webkit-flex;
            display: flex;
            flex-direction:row-reverse;    
        }
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If each li is set Width: 3000px; (current screen width 980px), effect:

# If the width of the child element exceeds, not only will there be no line wrapping, but it will automatically adapt to the size and be divided into 25%;

The above split will only be split equally in row. If it is arranged vertically:

flex-direction: column;
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The element will not be squeezed and has a width of 3000px ; But please note that it is not wrapped because of insufficient space, but the column value specifies its vertical arrangement.

The following values ​​can be adjusted to vertical arrangement in reverse order

flex-direction: column-reverse; //表示元素竖直 反向排
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flex -wrap

flex-wrap Default nowrap: no line wrapping. The above 3000px sub-element is precisely because this vertical position does not wrap by default, so the above setting is 3000px wide and will not wrap;

The same code, if you add an additional sentence

.box{
            display: -webkit-flex;
            display: flex;
            flex-direction: row-reverse;
            flex-wrap: wrap;    //换行,第一行在上方。
        }
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You can find that after setting it to wrap, the width of the sub-element becomes 100% of the screen width; this is like a flexible box stuffed into a box smaller than itself, and the flexible box automatically shrinks its own width.

If you write like this:

.box{
            display: -webkit-flex;
            display: flex;
            flex-direction: row-reverse;
            flex-wrap: wrap-reverse;    //换行,第一行在下方。
        }
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flex-flow

The flex-flow property is the flex-direction property and the abbreviation of flex-wrap property, the default value is row nowrap.

flex-flow:row wrap  ===  flex-direction:row; flex-wrap: wrap
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Change the code again:

.box{
      display: -webkit-flex;
      display: flex;
      flex-direction: row-reverse;
      flex-wrap: wrap-reverse;
    }
    
  可以写成

.box{
      display: -webkit-flex;
      display: flex;
      flex-flow:row-veverse wrap-reverse
    }
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justify-content

It has five values, among which if item is compared to the text of a word document , flex-star can be regarded as left-aligned, flex-end: right-aligned; flex-center: centered;

focus on the value space-around: equally divide the free space of the content, and the space on both sides of each item Equal;
Suppose the free space is an area and there are k sub-elements. How much margin is added to each sub-element? ==> area/2k

This example:

.item{
    width:200px;
}
.box{
       display: -webkit-flex;
       display: flex;
       justify-content: space-around;
}
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It is worth noting that the distance between items is one greater than the distance between the items and the border. times.

space-between: Align both ends, and the intervals between items are equal. Without the words

align-items

align, you can basically know that it is for the vertical direction;

.box{
            display: -webkit-flex;
            display: flex;
            justify-content: space-between;
            height: 1760px;
            align-items: center;

        }
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Remember to add a height to the parent; this way you can see that the element is vertically centered

Other similar attributes will not be written one by one

flex-start: Align the starting point of the cross axis.
flex-end: The end point alignment of the cross axis.
stretch (default value): If the item does not set a height or is set to auto, it will occupy the entire height of the container.

Look at the baseline attribute: the baseline alignment of the first line of text of the item.

This attribute is relatively new, you can try:

.box{
     align-items: baseline;
     }
     
    <ul class="box">
        <li class="item" style="height: 150px;line-height: 150px">1</li>
        <li class="item" style="height: 500px;line-height: 500px">2</li>
        <li class="item" style="height: 250px;line-height: 250px">3</li>
        <li class="item" style="height: 170px;line-height: 170px">4</li>
    </ul>
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Above I set different heights and line-heights for each item;

You can see that the container adjusts its position to align the text;

align-content

defines the alignment of multiple axes. This property has no effect if the project has only one axis.

.box{
            height: 1760px;   //高度要撑开
            display: -webkit-flex;
            display: flex;
            justify-content: space-between;
            flex-flow: row wrap; //横排 换行;产生多轴

        }
        
        
<ul class="box">
        <li class="item">1</li>
        <li class="item">2</li>
        <li class="item">3</li>
        <li class="item">4</li>
        <li class="item">5</li>
        <li class="item">6</li>
        <li class="item">7</li>
        <li class="item">8</li>
        <li class="item">9</li>
    </ul>
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Try to add code

align-content: flex-end;
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align-content:space-around;
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align-content:space-between;
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align-content : center;
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可以说,flex布局在父元素上对子元素垂直方向的控制还是非常到位和明确的;

子元素属性探究

order

大概可以理解为子元素的排队号码,默认都是0,越大排队越后;

<ul class="box">
        <li class="item" style="order:10">1</li>
        <li class="item" style="order:11">2</li>
        <li class="item">3</li>
        <li class="item">4</li>
        <li class="item">5</li>
        <li class="item">6</li>
        <li class="item">7</li>
        <li class="item">8</li>
        <li class="item">9</li>
    </ul>
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可以看到,1 号因为 order 设置为10排到了后面; 而2号因为更加大的order 而排到最后。

flex-grow 多余空间分配比例

它的值是一个number,默认为0;只要有一个同轴元素被设定了flex-grow ,所有多余空间都会按照这个比例分配,并让元素占满整行。这个被分配的空间,是算在自身里面的;

<ul class="box">
        <li class="item" style="flex-grow:1;">1</li>
        <li class="item" style="flex-grow:2;">2</li>
        <li class="item">3</li>
        <li class="item">4</li>
        <li class="item">5</li>
        <li class="item">6</li>
        <li class="item">7</li>
        <li class="item">8</li>
        <li class="item">9</li>
    </ul>
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盒子宽度变大了,(就是grow啦)

如果子元素有margin,那么会先计算横排多少个,再决定 flex-grow 分配的空间是多少

例如如下代码,

//没有设定 flex-grow 时
 <li class="item" style="flex-grow:0;margin: 0 100px;">1</li>
 <li class="item" style="flex-grow:0;">2</li>
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//设定了 flex-grow 时
 <li class="item" style="flex-grow:2;margin: 0 100px;">1</li>
 <li class="item" style="flex-grow:1;">2</li>
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所以,margin 并不算 多余空间 ,不会被重新分配;

flex-shrink

此属性与 flex-grow 有点相反的意思,用于处理 不换行时,内容超出屏幕了,应该决定谁来缩小;

值越大 缩小比例越大;默认是 1

改一下代码;

.box{
    flex-flow:row nowrap;
}

<ul class="box">
        <li class="item">1</li>
        <li class="item">2</li>
        <li class="item">3</li>
        <li class="item">4</li>
        <li class="item">5</li>
    </ul>
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此时 父盒子规定不能换行;但是5个item 宽度已经超过屏幕宽了;此时大家是等比缩小

下面设置1号 flex-shrink:600

<ul class="box">
        <li class="item" style="flex-shrink:600;">1</li>
        <li class="item">2</li>
        <li class="item">3</li>
        <li class="item">4</li>
        <li class="item">5</li>
    </ul>
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可以看到,尽管我把1号设置到缩放非常大了,但是实际宽度并没有很小;说明浏览器会自己决定内容是否已经足够放下,够了就停止缩放;

<ul class="box">
        <li class="item" style="flex-shrink:600;">1</li>
        <li class="item">2</li>
        <li class="item">3</li>
        <li class="item" style="flex-shrink:200;">4</li>
        <li class="item">5</li>
        <li class="item">6</li>
        <li class="item">7</li>
        <li class="item">8</li>
        <li class="item">9</li>
    </ul>
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当内容非常多时,1号就明显被缩放得非常厉害,同时我发现,4号尽管设置200,但是它的大小跟被设为600的 1号是一样的。

这是因为他们已经缩放到最后只能容纳文字的空间了;所以就不会再缩放下去;这跟文字占位一个道理

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。

简单来说,就是这个值会影响浏览器计算的输入值,有四种情况

1,本来就会超出,然后你设定的值比原值低(原值200px每个item),你的元素会被压缩。

 <ul class="box">
        <li class="item" style="flex-basis:100px;">1</li>
        <li class="item">2</li>
        <li class="item">3</li>
        <li class="item" style="">4</li>
        <li class="item">5</li>
        <li class="item">6</li>
        <li class="item">7</li>
        <li class="item">8</li>
        <li class="item">9</li>
    </ul>
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1,本来就会超出,然后你设定的值比原值大,你的元素会被相对放大些。

<ul class="box">
        <li class="item" style="flex-basis:600px;">1</li>
        <li class="item">2</li>
        <li class="item">3</li>
        <li class="item" style="">4</li>
        <li class="item">5</li>
        <li class="item">6</li>
        <li class="item">7</li>
        <li class="item">8</li>
        <li class="item">9</li>
    </ul>
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3 本来不会超出,你设定的值比原来小,你还是会小一点

 <ul class="box">
        <li class="item" style="flex-basis:100px;">1</li>
        <li class="item">2</li>
        <li class="item">3</li>
    </ul>
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4 本来不会超出,你设定的值比原来大,你就会更大

<ul class="box">
        <li class="item" style="flex-basis:600px;">1</li>
        <li class="item">2</li>
        <li class="item">3</li>
    </ul>
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这个值你可以当做宽度来看,当设定为 跟原来一样的值得时候,基本没有变化

<ul class="box">
        <li class="item" style="flex-basis:200px;">1</li>
        <li class="item">2</li>
        <li class="item">3</li>
    </ul>
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align-self

此子元素单独设置垂直方向对齐方式;默认auto 表示父亲怎么定义就怎么来;其他值跟align-items是一样的

<ul class="box">
        <li class="item" style="align-self: center">1</li>
        <li class="item" style="align-self: flex-end">2</li>
        <li class="item">3</li>
        <li class="item">4</li>
        <li class="item" style="align-self: center">5</li>
    </ul>
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此属性主要是方便特殊定位 某个字元素

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。

.item {
  flex: none | [ <&#39;flex-grow&#39;> <&#39;flex-shrink&#39;>? || <&#39;flex-basis&#39;> ]
}
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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。

最后

移动端使用flex 布局感觉还是非常给力的,并且通常满足各个屏幕自适应的要求;有机会还是要多实践起来。

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