html - 为什么 flex 元素不包装？

Question

我正在尝试制作具有相同高度的多行正方形(每行 3 个)。

我为此编写了一些 HTML 和 CSS，但这些框都在同一行上。

这是我目前所拥有的:

#list-wrapper {
  display: flex;
  width: 100%;
}
#list-wrapper div {
  width: 33.33%;
}
#list-wrapper div img {
  flex: 1;
}

<div id="list-wrapper">
  <div>
    <img src="images/1.png" alt="image one" />
  </div>
  <div>
    <img src="images/2.png" alt="image two" />
  </div>
  <div>
    <img src="images/1.png" alt="image one" />
  </div>
  <div>
    <img src="images/2.png" alt="image two" />
  </div>
  <div>
    <img src="images/1.png" alt="image one" />
  </div>
  <div>
    <img src="images/2.png" alt="image two" />
  </div>
</div>

当我用这个加载页面时，所有框都会出现，但它们都在一行上，超过父 div 的 100% 宽度。

Answer 1

flex 容器的初始设置是 flex-wrap: nowrap .

这意味着当您创建一个 flex 容器时(通过将 display: flex 或 display: inline-flex 应用于元素)所有子元素(“flex 元素” ) 仅限于一行。

使用 flex-wrap: wrap 来启用 flex items 的包装。

---

以下是 flex 属性如何工作的几个示例:

一个简单的 flex 容器，带有包含图像的各种 flex 元素:

#list-wrapper {
    display: flex;
    border: 1px solid black;
}

#list-wrapper div {}

#list-wrapper div img {
    height: 150px;
    width: 150px;
}

<div id="list-wrapper">
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
</div>

请注意，只声明了一个 flex 属性:display: flex。这建立了 flex 容器。以下行为是默认的:

• flex-wrap: nowrap
• flex-direction: row
• justify-content: flex-start

要允许元素换行，请添加 flex-wrap: wrap:

#list-wrapper {
    display: flex;
    flex-wrap: wrap; /* NEW */
    border: 1px solid black;
}

#list-wrapper div { }

#list-wrapper div img {
    height: 150px;
    width: 150px;
}

<div id="list-wrapper">
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
</div>

要每行只允许三个元素，请使用 flex属性:

#list-wrapper {
    display: flex;
    flex-wrap: wrap;
    border: 1px solid black;
}

#list-wrapper div {
    margin: 10px;
    flex: 1 1 calc(33.33% - 20px); /* flex-grow, flex-shrink, 
                                      flex-basis: (width - margin) */
}

#list-wrapper div img {
    height: 150px;
    width: 150px;
}

<div id="list-wrapper">
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
</div>

此外，默认情况下所有 flex 元素都具有相同的高度(align-items: stretch)。

#list-wrapper {
    display: flex;
    flex-wrap: wrap;
    border: 1px solid black;
}

#list-wrapper div {
    margin: 10px;
    flex: 1 1 calc(33.33% - 30px);
    border: 1px solid #ccc;
    background-color: lightgreen;
    text-align: center;
}

#list-wrapper div img {
    height: 150px;
    width: 150px;
}

<div id="list-wrapper">
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
</div>

如果恢复 flex-wrap: nowrap 并给容器一个高度，拉伸(stretch)会更明显:

#list-wrapper {
    display: flex;
    /* flex-wrap: wrap; */
    border: 1px solid black;
    height: 600px;
}

#list-wrapper div {
    margin: 10px;
    flex: 1 1 calc(33.33% - 30px);
    border: 1px solid #ccc;
    background-color: lightgreen;
    text-align: center;
}

#list-wrapper div img {
    height: 150px;
    width: 150px;
}

<div id="list-wrapper">
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
    <div><img src="http://i.imgur.com/60PVLis.png" alt=""></div>
</div>