flex-start 和基线有什么区别? [英] What's the difference between flex-start and baseline?

问题描述

使用 flex align-* 属性时，flex-start 和 baseline 有什么区别?

下面的代码片段为 align-self: flex-start 和 align-self:baseline 提供相同的输出.

在哪些情况下 align-self: flex-start 和 align-self:baseline 的行为会不同?

.flex-container {白颜色;显示:-webkit-flex；显示:弹性；宽度:350px；高度:200px；背景颜色:黄色；}.flex-item {背景颜色:绿色；宽度:50px；最小高度:100px；边距:10px；}.item1 {-webkit-align-self: flex-start;align-self: flex-start;}.item2 {-webkit-align-self: flex-end;align-self: flex-end;}.item3 {-webkit-align-self:居中；对齐自我:居中；}.item4 {-webkit-align-self:基线；对齐自我:基线；}.item5 {-webkit-align-self:拉伸；对齐自我:伸展；}

<div class="flex-item item1">flex-start</div><div class="flex-item item4">baseline</div><div class="flex-item item2">flex-end</div><div class="flex-item item3">center</div><div class="flex-item item5">stretch</div>

解决方案

请看以下两张图片.除了 align-items 规则外，两者的代码是相同的.

align-items: flex-start

align-items: 基线

当使用 align-items 或 align-self 时，flex-start 值将在 align-items 的起始边缘对齐弹性项目a href="https://stackoverflow.com/q/32551291/3597276">flex 容器的横轴.

baseline 值将沿其内容的基线对齐弹性项目.

<块引用>

^{来源:Wikipedia.org}

在许多情况下，当项目之间的字体大小相同(如问题中)，或者内容相同时，则 flex-start 和 baseline 将无法区分.

但是如果内容大小因弹性项目而异，那么 baseline 可以产生明显的差异.

就基线对齐发生的位置而言，由行中最高的项目决定.

来自规范:

<块引用>

8.3.跨轴对齐:align-items 和 align-self属性

基线

flex item 参与基线对齐:线上所有参与的 flex item 对齐，使得它们的基线对齐，并且其基线和它的 cross-start margin 之间距离最大的 item 被放置在与交叉对齐的位置线的起始边缘.

.flex-container {白颜色;显示:弹性；高度:300px；背景颜色:黄色；对齐内容:间隔；对齐项目:基线；}.flex-item {背景颜色:绿色；宽度:110px；最小高度:100px；边距:10px；box-sizing: 边框框；填充:5px；文本对齐:居中；}.item1 { 字体大小:2em;}.item2 { 字体大小:7em;}.item3 { 字体大小:.5em;}.item4 { 字体大小:3em;}.item5 { 字体大小:10em;}/*.item1 { align-self: flex-start;}.item2 { align-self: flex-end;}.item3 { 对齐自我:居中；}.item4 { align-self: 基线；}.item5 { align-self: 拉伸；}*/#虚线{边框:1px 红色虚线；位置:绝对；宽度:100%；顶部:170px；}

<div class="flex-item item1">A</div><div class="flex-item item2">B</div><div class="flex-item item3">C</div><div class="flex-item item4">D</div><div class="flex-item item5">E</div>
<div id="dashed-line"></div>

jsFiddle 版本

When working with flex align-* properties, what's the difference between flex-start and baseline?

The below code snippet gives same output for align-self: flex-start and align-self: baseline.

In which cases will align-self: flex-start and align-self: baseline behave differently?

.flex-container {
  color: white;
  display: -webkit-flex;
  display: flex;
  width: 350px;
  height: 200px;
  background-color: yellow;
}
.flex-item {
  background-color: green;
  width: 50px;
  min-height: 100px;
  margin: 10px;
}
.item1 {
  -webkit-align-self: flex-start;
  align-self: flex-start;
}
.item2 {
  -webkit-align-self: flex-end;
  align-self: flex-end;
}
.item3 {
  -webkit-align-self: center;
  align-self: center;
}
.item4 {
  -webkit-align-self: baseline;
  align-self: baseline;
}
.item5 {
  -webkit-align-self: stretch;
  align-self: stretch;
}

<div class="flex-container">
  <div class="flex-item item1">flex-start</div>
  <div class="flex-item item4">baseline</div>
  <div class="flex-item item2">flex-end</div>
  <div class="flex-item item3">center</div>
  <div class="flex-item item5">stretch</div>
</div>

解决方案

See the following two images. The code is identical for both, except for the align-items rule.

align-items: flex-start

align-items: baseline

When using align-items or align-self, the flex-start value will align flex items at the starting edge of the cross-axis of the flex container.

The baseline value will align flex items along their content's baseline.

baseline

The line upon which most letters "sit" and below which descenders extend.

^{Source: Wikipedia.org}

In many cases, when the font size is the same among items (like in the question), or the content is otherwise the same, then flex-start and baseline will be indistinguishable.

But if content size varies among flex items, then baseline can make a noticeable difference.

In terms of where baseline alignment occurs, that is determined by the tallest item in the row.

From the spec:

8.3. Cross-axis Alignment: the align-items and align-self properties

baseline

The flex item participates in baseline alignment: all participating flex items on the line are aligned such that their baselines align, and the item with the largest distance between its baseline and its cross-start margin edge is placed flush against the cross-start edge of the line.

.flex-container {
  color: white;
  display: flex;
  height: 300px;
  background-color: yellow;
  justify-content: space-between;
  align-items: baseline;
}
.flex-item {
  background-color: green;
  width: 110px;
  min-height: 100px;
  margin: 10px;
  box-sizing: border-box;
  padding: 5px;
  text-align: center;
}
.item1 {  font-size: 2em;  }
.item2 {  font-size: 7em;  }
.item3 {  font-size: .5em; }
.item4 {  font-size: 3em;  }
.item5 {  font-size: 10em; }

/*
.item1 {  align-self: flex-start; }
.item2 {  align-self: flex-end; }
.item3 {  align-self: center; }
.item4 {  align-self: baseline; }
.item5 {  align-self: stretch; }
*/

#dashed-line {
  border: 1px dashed red;
  position: absolute;
  width: 100%;
  top: 170px;
}

<div class="flex-container">
  <div class="flex-item item1">A</div>
  <div class="flex-item item2">B</div>
  <div class="flex-item item3">C</div>
  <div class="flex-item item4">D</div>
  <div class="flex-item item5">E</div>
</div>

<div id="dashed-line"></div>

jsFiddle version

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