为什么填充扩展一个flex项目? [英] Why is padding expanding a flex item?
问题描述
在下面的代码片段中,第一行有两个div,其中 flex-grow:1
。正如所料,每个div占用了屏幕的50%。
在向左div添加填充时,情况不再是这样。有人可以解释为什么吗?
body> div {height:50px; display:flex;} body> div> div {flex:1; box-sizing:border-box;}#a {background-color:red;}#b {background-color:green;}#c {padding:10px;
code>< DIV> < div id =a>< / div> < div id =b>< / div>< / div>< div> < div id =c>< / div> < div id =d>< / div>< / div>
弹性项目的大小与填充和<$ c 解决方案
$ c> flex-grow 由中的计算确定flexbox规格。
这些计算类似于使用填充和 flex-shrink
的弹性项目大小。
坦率地说,这个数学技术性很强,并不是世界上最容易理解的。
但是如果你想进入它的细节如下:
示例
下面是一些希望使行为更清晰的例子。 请记住, flex-grow
不是直接建立flex项目长度的工具。这是一个在柔性物品中分配容器空间的工具。 flex-basis
属性设置flex项目的初始主要大小。如果 flex-grow
与 flex-basis
一起使用,则问题中的问题已解决(请参阅下面的示例#4 )。
$ b $ p 示例#1
在块容器,您有 box-sizing:border-box
,代码中的框将平均呈现,不管填充情况如何。
body> div {height:50px; / *显示:flex; * / font-size:0; / *删除内嵌块空白* /} body> div> div {/ * flex:1; * / box-sizing:border-box; height:50px;显示:inline-block; width:50%;}#a {background-color:red;}#b {background-color:green;}#c {padding:10px; background-color:blue;}#d {background-color:yellow;
< DIV> < div id =a>< / div> < div id =b>< / div>< / div>< div> < div id =c>< / div> < div id =d>< / div>< / div>
示例2
在 flex容器中,其中你有 box-sizing:border-box
和 width
或 > flex-basis
来计算不管填充情况如何,这些方块都会呈现均匀。
body> div {height:50px;显示:flex; } body> div> div {flex-basis:50%; / *宽度:50%;这个工程,以及* / box-sizing:border-box;}#a {background-color:red;}#b {background-color:green;}#c {padding:10px; background-color:blue;}#d {background-color:yellow;
< DIV> < div id =a>< / div> < div id =b>< / div>< / div>< div> < div id =c>< / div> < div id =d>< / div>< / div>
示例#3 在Flex容器中,您有 box-sizing:border-box
和 flex-grow
,它会出现 box-sizing code>不起作用...
body> div {height:50px;显示:flex; } body> div> div {flex:1; / * flex-basis:50%; * / / *宽度:50%;这个工程,以及* / box-sizing:border-box;}#a {background-color:red;}#b {background-color:green;}#c {padding:10px; background-color:blue;}#d {background-color:yellow;
< DIV> < div id =a>< / div> < div id =b>< / div>< / div>< div> < div id =c>< / div> < div id =d>< / div>< / div>
但这并不正确......
示例#4
flex-grow
根据flex容器中的可用空间展开Flex项目的宽度。换句话说,它忽略填充(和边框)。然而,如果您只是指定 flex-grow
以及 flex-basis code>,
边界框
可以工作:
flex:1 1 50%; / * flex-grow,flex-shrink,flex-basis * /
body> div {height:50px;显示:flex; } body> div> div {flex:1 1 50%; / * flex-grow,flex-shrink,flex-basis * / / * flex-basis:50%; * / / *宽度:50%;这个工程,以及* / box-sizing:border-box;}#a {background-color:red;}#b {background-color:green;}#c {padding:10px; background-color:blue;}#d {background-color:yellow;
< DIV> < div id =a>< / div> < div id =b>< / div>< / div>< div> < div id =c>< / div> < div id =d>< / div>< / div>
In the snippet below, the first row has two divs with flex-grow: 1
. As expected, each div takes up 50% of the screen.
When adding padding to the left div, that is no longer the case. Can someone explain why?
body > div {
height: 50px;
display: flex;
}
body > div > div {
flex: 1;
box-sizing: border-box;
}
#a {
background-color: red;
}
#b {
background-color: green;
}
#c {
padding: 10px;
background-color: blue;
}
#d {
background-color: yellow;
}
<div>
<div id="a"></div>
<div id="b"></div>
</div>
<div>
<div id="c"></div>
<div id="d"></div>
</div>
The calculations are defined in the spec.
A flex item's size with padding and flex-grow
is determined by calculations in the flexbox spec.
These calculations are similar to the sizing of flex items with padding and flex-shrink
.
Frankly, the math is quite technical and not the easiest thing in the world to understand.
But if you want to get into it, here are the details:
Examples
Below are examples that hopefully make the behavior more clear.
NOTE: Keep in mind that flex-grow
is not a tool for directly establishing the length of a flex item. It's a tool for distributing space in the container among flex items. The flex-basis
property sets the initial main size of a flex item. If flex-grow
is used with flex-basis
, the problem in the question is resolved (see example #4 below).
Example #1
In a block container, where you have box-sizing: border-box
, the boxes in your code will render evenly regardless of padding.
body > div {
height: 50px;
/* display: flex; */
font-size: 0; /* remove inline block whitespace */
}
body > div > div {
/* flex: 1; */
box-sizing: border-box;
height: 50px;
display: inline-block;
width: 50%;
}
#a {
background-color: red;
}
#b {
background-color: green;
}
#c {
padding: 10px;
background-color: blue;
}
#d {
background-color: yellow;
<div>
<div id="a"></div>
<div id="b"></div>
</div>
<div>
<div id="c"></div>
<div id="d"></div>
</div>
Example #2
In a flex container, where you have box-sizing: border-box
, and the width
or flex-basis
is used to calculate length, the boxes will render evenly regardless of padding.
body > div {
height: 50px;
display: flex;
}
body > div > div {
flex-basis: 50%;
/* width: 50%; this works, as well */
box-sizing: border-box;
}
#a {
background-color: red;
}
#b {
background-color: green;
}
#c {
padding: 10px;
background-color: blue;
}
#d {
background-color: yellow;
<div>
<div id="a"></div>
<div id="b"></div>
</div>
<div>
<div id="c"></div>
<div id="d"></div>
</div>
Example #3
In a flex container, where you have box-sizing: border-box
and flex-grow
, it will appear that box-sizing
doesn't work...
body > div {
height: 50px;
display: flex;
}
body > div > div {
flex: 1;
/* flex-basis: 50%; */
/* width: 50%; this works, as well */
box-sizing: border-box;
}
#a {
background-color: red;
}
#b {
background-color: green;
}
#c {
padding: 10px;
background-color: blue;
}
#d {
background-color: yellow;
<div>
<div id="a"></div>
<div id="b"></div>
</div>
<div>
<div id="c"></div>
<div id="d"></div>
</div>
but that's not really correct...
Example #4
flex-grow
expands the width of a flex item based on available space in the flex container. In other words, it ignores padding (and borders).
However, if you simply specify flex-grow
along with flex-basis
, the border-box
will work:
flex: 1 1 50%; /* flex-grow, flex-shrink, flex-basis */
body > div {
height: 50px;
display: flex;
}
body > div > div {
flex: 1 1 50%; /* flex-grow, flex-shrink, flex-basis */
/* flex-basis: 50%; */
/* width: 50%; this works, as well */
box-sizing: border-box;
}
#a {
background-color: red;
}
#b {
background-color: green;
}
#c {
padding: 10px;
background-color: blue;
}
#d {
background-color: yellow;
<div>
<div id="a"></div>
<div id="b"></div>
</div>
<div>
<div id="c"></div>
<div id="d"></div>
</div>
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