让我们来看看如何使用 CSS3 的弹性布局写出 10 种常见的 UI 组件。
翻译自 Flexbox Patterns
Flexbox CSS 的基础属性就是 display: flex ，只需要给元素添加这个属性，你就用上了弹性布局了。就这么简单！
你也许会问，这个属性起了什么作用？默认情况下，它指定了容器中的子元素沿主轴（main axis）排列，主轴默认是水平方向的。
接下来，我们会用两个实例来介绍这个属性是如何用在我们的 UI 组件的。
我们要介绍的第一个例子是步进输入框组件。当绑定 JavaScript 代码之后，点击 + / - 号，输入框中的值将会对应增加 / 减少。
译注：此处计数器的实现也可以使用 CSS Counters 来代替 JavaScript，具体例子可以参考 使用 CSS 的 counter-increment 做的游戏 。
按照以往的思路，你可能会选择用 display: inline-block 或者 float: left 来实现这种内联样式。然而，这样做的话，你还需要给这些元素统统添加特定的选择器。让我们使用弹性盒子吧，只需要往容器添加 display: flex 属性，就可以实现相同的效果了。
当你添加这个属性时，相当于对元素说：“嘿伙计，你就负责按照 flexbox 的规则排列你的子元素就好了！”。在最基本的形式下，元素沿主轴（main axis）排列，默认就是 x 轴，从左到右。
CSS 代码
.stepperInput { /** * Setting display to flex makes this container lay * out its children using flexbox. By default, it * orders items horizontally, top-aligned. * This has a similar effect to setting the children * to have display: inline-block. */ display: flex;}.stepperInput__input { border-left: 0; border-right: 0; width: 60px; text-align: center;}.button { cursor: pointer; padding: 5px 15px; color: #FFFFFF; background-color: #4EBBE4; font-size: 12px; border: 1px solid #16A2D7; border-radius: 4px;}.button--addOnLeft { border-top-right-radius: 0; border-bottom-right-radius: 0;}.button--addOnRight { border-top-left-radius: 0; border-bottom-left-radius: 0;}.input { border: 1px solid #D7DBDD; padding: 0 10px; border-radius: 0; box-shadow: none;}HTML 代码
<div class="stepperInput"> <button class="button button--addOnLeft">-</button> <input type="text" placeholder="Age" value="32" class="input stepperInput__input"/> <button class="button button--addOnRight">+</button></div>
同理，使用 display: flex 也可以实现这种标签页效果。
CSS 代码
.tabs { /** * Setting display to flex makes this container lay * out its children using flexbox, the exact same * as in the above "Stepper input" example. */ display: flex; border-bottom: 1px solid #D7DBDD;}.tab { cursor: pointer; padding: 5px 30px; color: #16A2D7; font-size: 12px; border-bottom: 2px solid transparent;}.tab.is-tab-selected { border-bottom-color: #4EBBE4;}HTML 代码
<div class="tabs"> <div class="tab is-tab-selected">Tab 1</div> <div class="tab">Tab 2</div> <div class="tab">Tab 3</div> <div class="tab">Tab 4</div></div>
译注：tab 的切换效果可以通过纯 CSS 实现，可以参考 CSS trick for tabs without javascript demo
你可以把这种组件作为网站或者 webapp 的顶部。
要构建这种组件，典型方法是把 logo 和导航按钮包裹在一个容器，设置按钮放在另一个容器中。然后，使用 float 把两个容器方别推向两边。紧接着，你要对整个顶部元素清楚浮动。对于一个简单布局而言，这也太复杂了。
如果使用弹性盒子，你依然需要容器元素，但是你不需要为容器添加特定的样式了，因为 flexbox 已经让父元素来负责布局了。
除开 display: flex 属性外，我们还需要另外两个属性来调整布局：
.siteHeader { /** * Lay out the children of this container with * flexbox, which is horizontal by default. */ display: flex; /** * Make the container put as much space as possible * between its children, with the children at either * end laying flush against the container's edges. */ justify-content: space-between; padding: 10px; background-color: #56727C;}.siteHeader__section { /** * Lay out the children of this container with * flexbox. */ display: flex; /** * Align the children in the center, along * the main axis. By default the children will * align along their top edges. */ align-items: center;}.siteHeader__item { padding: 5px 15px; font-size: 12px;}.siteHeader__item + .siteHeader__item { margin-left: 5px;}.siteHeader__item.is-site-header-item-selected { color: #FFFFFF; background-color: #415F69; border-radius: 4px;}.siteHeaderLogo { font-size: 20px; line-height: 0; color: white;}.siteHeaderButton { cursor: pointer; color: #D9E9EF;}<div class="siteHeader"> <!-- This section gets pushed to the left side--> <div class="siteHeader__section"> <div class="siteHeader__item siteHeaderLogo"> <div class="fa fa-inbox"></div> </div> <div class="siteHeader__item siteHeaderButton is-site-header-item-selected">Inbox</div> <div class="siteHeader__item siteHeaderButton">Sent</div> <div class="siteHeader__item siteHeaderButton">Trash</div> </div> <!-- This section gets pushed to the right side--> <div class="siteHeader__section"> <div class="siteHeader__item siteHeaderButton">Settings</div> </div></div>
你也许需要在表单底部放个进度圈或者验证反馈。和上面的例子类似，使用弹性盒子可以将这些内容和表单提交按钮分隔开来。
CSS 代码
.formFooter { /** * Lay out the children of this container with * flexbox, which is horizontal by default. */ display: flex; /** * Align the children in the center, along * the main axis, which is horizontal in this case. */ align-items: center; /** * Make the container put as much space as possible * between its children, with the children at either * end laying flush against the container's edges. */ justify-content: space-between; border-top: 1px solid #D7DBDD; padding: 10px;}.formFooter__section { /** * This container orders items horizontally. */ display: flex; /** * It aligns them vertically in the center. */ align-items: center;}.formFooter__item + .formFooter__item { margin-left: 5px;}.formFooterFeedback { color: #86969C; font-size: 12px; line-height: 0;}.formFooterSpinner { animation: formFooterSpinner 1s infinite steps(8, end);}@keyframes formFooterSpinner { 0% { transform: rotate(0deg); } 100% { transform: rotate(360deg); }}.button--clear { color: #16A2D7; background-color: #FFFFFF; border: 1px solid #FFFFFF;}HTML 代码
<div class="formFooter"> <!-- This section gets pushed to the left side--> <div class="formFooter__section"> <div class="formFooter__item formFooterFeedback"> <div class="fa fa-spinner formFooterSpinner"></div> Saving... </div> </div> <!-- This section gets pushed to the right side--> <div class="formFooter__section"> <div class="formFooter__item button button--clear">Reset</div> <div class="formFooter__item button">Save</div> </div></div>
这也是一个相当经典的组件。你甚至不需要 flexbox 来构造它，div 就足够了…… 不过，如果设计师让你把其中一个按钮单独拿到下面，你可以用 position: absolute 来处理，当然也可以用 flexbox。
除了 display: flex 和 justify-content: space-between ，我们还需要另一个属性：
CSS 代码
.sideBar { /** * This container orders items according to flexbox * rules. By default, this would arrange its children * horizontally. However, the next property... */ display: flex; /** * ...sets the main axis to be vertical instead of * horizontal, so now the children are laid out * vertically, from top to bottom. */ flex-direction: column; /** * It will also put as much space as possible * between its children, with the children at either end * laying flush against the container's edges. */ justify-content: space-between; height: 300px; width: 150px; border-right: 1px solid #D7DBDD; background-color: #FCFDFD; padding: 10px;}.sideBar__item { cursor: pointer; padding: 5px 10px; color: #16A2D7; font-size: 12px;}.sideBar__item.is-side-bar-item-selected { background-color: #EEF3F5; border-radius: 4px;}HTML 代码
<div class="sideBar"> <!-- This section gets pushed to the top--> <div class="sideBar__section"> <div class="sideBar__item is-side-bar-item-selected">Inbox</div> <div class="sideBar__item">Contacts</div> <div class="sideBar__item">Account</div> </div> <!-- This section gets pushed to the bottom--> <div class="sideBar__section"> <div class="sideBar__item">Legal</div> </div></div>
不使用 flexbox 的居中布局通常需要一些 hack 技巧，比如使用绝对布局然后通过 2D transform 平移。使用 flexbox，你只需要在容器元素设置 4 个属性：
CSS 代码
.centeredPrompt { /** * Lay out the children of this container with * flexbox. */ display: flex; /** * Rotate the main axis so that the children * are laid out vertically, the same as in the * above "Side bar" example. */ flex-direction: column; /** * Align the children in the center, along * the main axis. Because the direction is * "column" this has a similar effect as setting * text-align: center. */ align-items: center; /** * Instead of pushing the children apart, as in * previous examples, we will group them together * in the center of their container. */ justify-content: center; min-height: 300px; padding: 10px;}.centeredPrompt__item + .centeredPrompt__item { margin-top: 5px;}.centeredPromptIcon { font-size: 60px; line-height: 0;}.centeredPromptLabel { color: #86969C; font-size: 30px; font-weight: 700; text-align: center;}.centeredPromptDetails { color: #86969C; font-size: 16px; margin-bottom: 10px; text-align: center;}.icon { color: #BCD2DA;}HTML 代码
<div class="centeredPrompt"> <div class="centeredPrompt__item centeredPromptIcon"> <div class="icon fa fa-smile-o"></div> </div> <div class="centeredPrompt__item centeredPromptLabel">Welcome to the app!</div> <div class="centeredPrompt__item centeredPromptDetails">Thanks for signing up. Let’s take a look around.</div> <div class="centeredPrompt__item button">Begin tour</div></div>
使用同样的方法，我们还可以居中更多东西，比如图标。
CSS 代码
.centeredIcon { /** * Lay out the children of this container with * flexbox. */ display: flex; /** * As in the above "Centered prmopt" example, * we'll rotate the main axis so that the children * are ordered vertically. */ flex-direction: column; /** * And just like in that example, align the children * in the center, along the main axis. */ align-items: center; /** * Same thing here as before: group the children * together in the center of their container. */ justify-content: center; border: 1px solid #D7DBDD; font-size: 40px; width: 90px; height: 90px; border-radius: 100%; box-shadow: 0 2px 1px rgba(0, 0, 0, 0.05), 0 2px 3px rgba(0, 0, 0, 0.05), 0 4px 8px rgba(0, 0, 0, 0.05);}HTML 代码
<div class="centeredIcon"> <div class="icon fa fa-phone"></div></div>
在这个列表中，其中一行是反向排列的，实现方法很简单，只需要添加一个 flexbox 属性：
flex-direction: row-reverse 把容器中的子元素按照 HTML 中的顺序反向排列。
CSS 代码
.featureListItem { /** * Lay out the children of this container with * flexbox, which is horizontal by default. */ display: flex; /** * Align the children in the center, along * the main axis, which is horizontal in this case. */ align-items: center; max-width: 400px; padding: 10px;}.featureListItem + .featureListItem { border-top: 1px solid #D7DBDD;}.featureListItem--reverse { /** * We can specify the flex-direction so that * the children elements are displayed in the * reverse order of how they appear in the * markup. */ flex-direction: row-reverse;}.featureListItem__icon,.featureListItem__description { padding: 5px 15px;}.featureListItem__icon { font-size: 50px; line-height: 0;}.featureListItem__description { color: #86969C; font-size: 12px;}HTML 代码
<div class="featureListItem"> <div class="featureListItem__icon"> <div class="icon fa fa-calendar"></div> </div> <div class="featureListItem__description">The calendar feature makes scheduling a snap.</div></div><div class="featureListItem featureListItem--reverse"> <div class="featureListItem__icon"> <div class="icon fa fa-dashboard"></div> </div> <div class="featureListItem__description">Our dashboard gives you a bird’s-eye-view-at-a-glance-on-the-go.</div></div><div class="featureListItem"> <div class="featureListItem__icon"> <div class="icon fa fa-envelope"></div> </div> <div class="featureListItem__description">You can get notified by email or SMS.</div></div>
接下来复习一下，这个卡片的组件用到了此前提到的属性。
这里没什么新的知识点，但是为我们接下来要介绍的卡片组做了铺垫。
CSS 代码
.card { /** * Lay out the children of this container with * flexbox, which is horizontal by default. */ display: flex; /** * Rotate the main axis so that the children * are laid out vertically. */ flex-direction: column; border: 1px solid #CAD0D2; border-radius: 4px; overflow: hidden;}.card__description { /** * Lay out the children of this container with * flexbox. */ display: flex; /** * We're going to lay out this element's children * just like in the "Centered prompt" example. * First we'll rotate the main axis so that the * children are laid out vertically. */ flex-direction: column; /** * Just like in the "Centered prompt" example, * we'll align the children in the center, along * the main axis. */ align-items: center; /** * And just like in the "Centered prompt", we'll * group the children in the center of their * container. */ justify-content: center; padding: 15px;}.card__descriptionIcon { font-size: 32px; margin-bottom: 10px;}.card__descriptionText { color: #57727C; font-size: 12px; text-align: center;}.card__price { text-align: center; color: #57727C; font-size: 12px; font-weight: 700; padding: 5px 15px; border-top: 1px solid #D7DBDD; background-color: #EEF3F5;}.card--fixedWidth { max-width: 120px;}HTML 代码
<div class="card card--fixedWidth"> <div class="card__description"> <div class="icon fa fa-flask card__descriptionIcon"></div> <div class="card__descriptionText">Science potion</div> </div> <div class="card__price">Costs $5</div></div>
现在我们来学习最后一个 “卡片组” 组件。我们需要考虑两个麻烦的地方：
不适用 flexbox，你可能会想到使用 table 元素来实现这些需求，或者对所有元素使用绝对布局，并组合使用百分比、像素和 calc() 来实现。这样也太复杂了。
使用弹性盒子，整个问题的解决方案就变得优雅多了。这里我们引入一个新的属性，但是和之前我们提到的属性不同，这个属性应用在 子元素 而不是容器。
我们为每张卡片设置 flex: 1 1 0 ，使得每张卡片的宽度相等。这个属性是以下三个属性的简写方法：
这些属性满足了第一点要求。对于我们的第二个要求，我们可以对 flex 属性稍作调整，改成 flex: 1 1 auto 。
.cardGroup { /** * Lay out the children of this container with * flexbox, which is horizontal by default. */ display: flex; border: 1px solid #CAD0D2; border-radius: 4px; overflow: hidden;}.cardGroup__card { /** * The flex property is a short-hand for setting * the flex-shrink, flex-grow, and flex-basis * properties. These properties control how the * element resizes to fill its container. * * We'll also set flex-grow to 1 so that it * will expand to fill its container. (The * default value is 0.) * * We'll set flex-shrink to 1 so that the element * will shrink as its container gets smaller. * (The default value is 1.) * * Last, we set flex-basis to 0 so that its * size is solely determined by the size of * the container. (The default value * is auto, which would cause the content's * size to also be a factor in this calculation.) * * The net result of these properties is that the * element is a fluid size, and will expand and * shrink with its container and siblings, but * they will all have the same size, even if they * have different amounts of content. */ flex: 1 1 0; border: none; border-radius: 0;}.cardGroup__card + .cardGroup__card { border-left: 1px solid #D7DBDD;}.cardGroup__cardDescription { /** * We're doing almost the exact same thing here as * we did above. The difference is that its * flex-basis is auto, so now the size of its content * will affect how large it is. */ flex: 1 1 auto;}<div class="cardGroup"> <div class="card cardGroup__card"> <div class="card__description cardGroup__cardDescription"> <div class="icon fa fa-thumbs-o-up card__descriptionIcon"></div> <div class="card__descriptionText">Trial</div> </div> <div class="card__price">Free!</div> </div> <div class="card cardGroup__card"> <div class="card__description cardGroup__cardDescription"> <div class="icon fa fa-trophy card__descriptionIcon"></div> <div class="card__descriptionText">Basic tier<br/>(most popular)</div> </div> <div class="card__price">$10.00</div> </div> <div class="card cardGroup__card"> <div class="card__description cardGroup__cardDescription"> <div class="icon fa fa-bolt card__descriptionIcon"></div> <div class="card__descriptionText">Advanced tier<br/>(only for enterprise-level professionals)</div> </div> <div class="card__price">$6,000.00</div> </div></div>
