深入理解BootStrap-- 下拉菜单8

1、下拉菜单（基本用法）

小伙伴们注意，在Bootstrap框架中的下拉菜单组件是一个独立的组件，根据不同的版本，它对应的文件：

☑ LESS版本：对应的源码文件为 dropdowns.less

☑ Sass版本：对应的源码文件为 _dropdowns.sass

☑ 编译后的Bootstrap版本：查看bootstrap.css文件第3004行～第3130行

在使用Bootstrap框架的下拉菜单时，必须调用Bootstrap框架提供的bootstrap.js文件。当然，如果你使用的是未编译版本，在js文件夹下你能找到一个名为“dropdown.js”的文件。你也可以调用这个js文件。不过在我们的教程中，我们统一调用压缩好的“bootstrap.min.js”文件：

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">src</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"</span>></span><span class="javascript" style="box-sizing: border-box;"></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

特别声明：因为Bootstrap的组件交互效果都是依赖于jQuery库写的插件，所以在使用bootstrap.min.js之前一定要先加载jquery.min.js才会生效果。

我们先来看官网上一个简单的示例：

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown"</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"btn btn-default dropdown-toggle"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">type</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"button"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">id</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdownMenu1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">data-toggle</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown"</span>></span>
下拉菜单
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">span</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"caret"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">span</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">ul</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown-menu"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menu"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">aria-labelledby</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdownMenu1"</span>></span>
   <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>下拉菜单项<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
   …
   <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"divider"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
   <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>下拉菜单项<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">ul</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul>

使用方法：

在使用Bootstrap框架中的下拉菜单组件时，其结构运用的正确与否非常的重要，如果结构和类名未使用正确，直接影响组件是否能正常运用。我们来简单的看看：

1、使用一个名为“dropdown”的容器包裹了整个下拉菜单元素，示例中为:

2、使用了一个<button>按钮做为父菜单，并且定义类名“dropdown-toggle”和自定义“data-toggle”属性，且值必须和最外容器类名一致，此示例为:

<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">data</span><span class="hljs-attribute" style="box-sizing: border-box;">-toggle</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span><span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dropdown"</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

3、下拉菜单项使用一个ul列表，并且定义一个类名为“dropdown-menu”，此示例为:

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><ul <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span>=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dropdown-menu"</span>></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

示例

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-doctype" style="color: rgb(102, 0, 102); box-sizing: border-box;"><!DOCTYPE HTML></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">html</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">head</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">meta</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">http-equiv</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"Content-Type"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">content</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"text/html; charset=utf-8"</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">title</span>></span>下拉菜单<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">title</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">link</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">rel</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"stylesheet"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css"</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">head</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">body</span>></span>

<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown"</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"btn btn-default dropdown-toggle"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">type</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"button"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">id</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdownMenu1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">data-toggle</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown"</span>></span>
    选择你喜欢的水果
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">span</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"caret"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">span</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">ul</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown-menu"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menu"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">aria-labelledby</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdownMenu1"</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>苹果<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>香蕉<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>梨<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>桃<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">ul</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span>></span> 
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">src</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"http://libs.baidu.com/jquery/1.9.0/jquery.js"</span>></span><span class="javascript" style="box-sizing: border-box;"></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">src</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"</span>></span><span class="javascript" style="box-sizing: border-box;"></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span>></span> 
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">body</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">html</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li></ul>

2、下拉菜单（原理分析）

Bootstrap框架中的下拉菜单组件，其下拉菜单项默认是隐藏的，如下所示：

因为“dropdown-menu”默认样式设置了“display:none”，其详细源码请查看bootstrap.css文件第3010行～第3029行：

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">position</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> absolute</span></span>;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*设置绝对定位，相对于父元素div.dropdown*/</span>
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">top</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">100</span>%</span></span>;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*让下拉菜单项在父菜单项底部，如果父元素不设置相对定位，该元素相对于body元素*/</span>
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">left</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">0</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">z-index</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">1000</span></span></span>;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*让下拉菜单项不被其他元素遮盖住*/</span>

  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">display</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> none</span></span>;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*默认隐藏下拉菜单项*/</span>

  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">float</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> left</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">min-width</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">160</span>px</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">padding</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">5</span>px <span class="hljs-number" style="box-sizing: border-box;">0</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">margin</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">2</span>px <span class="hljs-number" style="box-sizing: border-box;">0</span> <span class="hljs-number" style="box-sizing: border-box;">0</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">font-size</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">14</span>px</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">list-style</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> none</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">background-color</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-hexcolor" style="box-sizing: border-box;">#fff</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">background-clip</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> padding-box</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">border</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">1</span>px solid <span class="hljs-hexcolor" style="box-sizing: border-box;">#ccc</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">border</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">1</span>px solid <span class="hljs-function" style="box-sizing: border-box;">rgba(<span class="hljs-number" style="box-sizing: border-box;">0</span>, <span class="hljs-number" style="box-sizing: border-box;">0</span>, <span class="hljs-number" style="box-sizing: border-box;">0</span>, .<span class="hljs-number" style="box-sizing: border-box;">15</span>)</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">border-radius</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">4</span>px</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">-webkit-box-shadow</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">0</span> <span class="hljs-number" style="box-sizing: border-box;">6</span>px <span class="hljs-number" style="box-sizing: border-box;">12</span>px <span class="hljs-function" style="box-sizing: border-box;">rgba(<span class="hljs-number" style="box-sizing: border-box;">0</span>, <span class="hljs-number" style="box-sizing: border-box;">0</span>, <span class="hljs-number" style="box-sizing: border-box;">0</span>, .<span class="hljs-number" style="box-sizing: border-box;">175</span>)</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">box-shadow</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">0</span> <span class="hljs-number" style="box-sizing: border-box;">6</span>px <span class="hljs-number" style="box-sizing: border-box;">12</span>px <span class="hljs-function" style="box-sizing: border-box;">rgba(<span class="hljs-number" style="box-sizing: border-box;">0</span>, <span class="hljs-number" style="box-sizing: border-box;">0</span>, <span class="hljs-number" style="box-sizing: border-box;">0</span>, .<span class="hljs-number" style="box-sizing: border-box;">175</span>)</span></span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li></ul>

当用户点击父菜单项时，下拉菜单将会被显示出来，当用户再次点击时，下拉菜单将继续隐藏。

原理分析：

现在我们来分析一下实现原理，非常简单，通过js技术手段，给父容器“div.dropdown”添加或移除类名“open”来控制下拉菜单显示或隐藏。也就是说，默认情况，“div.dropdown”没有类名“open”，当用户第一次点击时，“div.dropdown”会添加类名“open”；当用户再次点击时，“div.dropdown”容器中的类名“open”又会被移除。我们可以通过浏览器的firebug查看整个过程：

默认情况：

用户第一次点击：

用户再次点击：

在bootstrap.css文件第3076行～第3078行，我们可以很容易发现：

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.open</span> > <span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">display</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> block</span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

3、下拉菜单（下拉分隔线）

在Bootstrap框架中的下拉菜单还提供了下拉分隔线，假设下拉菜单有两个组，那么组与组之间可以通过添加一个空的<li>，并且给这个<li>添加类名“divider”来实现添加下拉分隔线的功能。对应的样式代码：

/源码bootstrap.css文件第3034行～第3039行/

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> <span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.divider</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">height</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">1</span>px</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">margin</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">9</span>px <span class="hljs-number" style="box-sizing: border-box;">0</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">overflow</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> hidden</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">background-color</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-hexcolor" style="box-sizing: border-box;">#e5e5e5</span></span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

示例：

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-doctype" style="color: rgb(102, 0, 102); box-sizing: border-box;"><!DOCTYPE HTML></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">html</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">head</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">meta</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">http-equiv</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"Content-Type"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">content</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"text/html; charset=utf-8"</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">title</span>></span>下拉分隔线<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">title</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">link</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">rel</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"stylesheet"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css"</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">link</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">rel</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"stylesheet"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"style.css"</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">head</span>></span>

<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">body</span>></span>
 <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown"</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"btn btn-default dropdown-toggle"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">type</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"button"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">id</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdownMenu1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">data-toggle</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown"</span>></span>
    食物
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">span</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"caret"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">span</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">ul</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown-menu"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menu"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">aria-labelledby</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdownMenu1"</span>></span>

    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>芹菜<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>萝卜<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>茄子<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
     <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span> =<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"divider"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>米饭<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>馒头<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>面条<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">ul</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span>></span> 
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">src</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"http://libs.baidu.com/jquery/1.9.0/jquery.js"</span>></span><span class="javascript" style="box-sizing: border-box;"></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">src</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"</span>></span><span class="javascript" style="box-sizing: border-box;"></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">script</span>></span> 
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">body</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">html</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li></ul>

效果如下：

4、下拉菜单（菜单标题）

上一小节讲解通过添加“divider”可以将下拉菜单分组，为了让这个分组更明显，还可以给每个组添加一个头部（标题）。如下：

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown-header"</span>></span>第一部分菜单头部<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

对应的样式如下：

/查看bootstrap.css文件第3090行～第3096行/

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-header</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">display</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> block</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">padding</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">3</span>px <span class="hljs-number" style="box-sizing: border-box;">20</span>px</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">font-size</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">12</span>px</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">line-height</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">1.42857143</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">color</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-hexcolor" style="box-sizing: border-box;">#999</span></span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

示例

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown"</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"btn btn-default dropdown-toggle"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">type</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"button"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">id</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdownMenu1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">data-toggle</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown"</span>></span>
    食物
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">span</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"caret"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">span</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">ul</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown-menu"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menu"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">aria-labelledby</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdownMenu1"</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown-header"</span>></span>蔬菜<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>芹菜<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>萝卜<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>茄子<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"divider"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown-header"</span>></span>主食<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>米饭<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>馒头<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>面条<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">ul</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span>></span> </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>

运行效果如下： 

5、下拉菜单（对齐方式）

实现右对齐方法：

Bootstrap框架中下拉菜单默认是左对齐，如果你想让下拉菜单相对于父容器右对齐时，可以在“dropdown-menu”上添加一个“pull-right”或者“dropdown-menu-right”类名，如下所示：

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><ul <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span>=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dropdown-menu pull-right"</span> role=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"menu"</span> aria-labelledby=<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"dropdownMenu1"</span>></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

上面代码中的“pull-right”类可以用“dropdown-menu-right”代替，两个类的作用是一样的，可从下面的源代码中看出。

实现原理：

对应的样式如下：

/源码请查看bootstrap.css文件第3030行～第3033行和3082行～第3085行/

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.pull-right</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">right</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">0</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">left</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> auto</span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span>
<span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu-right</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">right</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">0</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">left</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> auto</span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

同时一定要为.dropdown添加float:leftcss样式。

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown</span><span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">float</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> left</span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

运行效果如下所示： 

下拉菜单与父容器左边对齐:

与此同时，还有一个类名刚好与“dropdown-menu-right”相反的类名“dropdown-menu-left”，其效果就是让下拉菜单与父容器左边对齐，其实就是默认效果。

/请查看bootstrap.css文件第3086行～第3089行/

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu-left</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">right</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> auto</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">left</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">0</span></span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

6、下拉菜单（菜单项状态）

下拉菜单项的默认的状态（不用设置）有悬浮状态（:hover）和焦点状态（:focus）：

/查看bootstrap.css文件第3049行～第3054行/

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">li</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">a</span><span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:hover</span>,
<span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">li</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">a</span><span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:focus</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">color</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-hexcolor" style="box-sizing: border-box;">#262626</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">text-decoration</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> none</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">background-color</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-hexcolor" style="box-sizing: border-box;">#f5f5f5</span></span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

下拉菜单项除了上面两种状态，还有当前状态（.active）和禁用状态（.disabled）。这两种状态使用方法只需要在对应的菜单项上添加对应的类名：

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown"</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"btn btn-default dropdown-toggle"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">type</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"button"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">id</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdownMenu1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">data-toggle</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown"</span>></span>
  下拉菜单
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">span</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"caret"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">span</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">ul</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdown-menu"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menu"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">aria-labelledby</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"dropdownMenu1"</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"active"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>下拉菜单项<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
    ….
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"presentation"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"disabled"</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">role</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"menuitem"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">tabindex</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"-1"</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">href</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"#"</span>></span>下拉菜单项<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">a</span>></span><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">li</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">ul</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>

运行效果如下：

对应的样式代码也非常简单：

/请查看bootstrap.css文件第3055行～第3075行/

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> > <span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.active</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">a</span>,
<span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> > <span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.active</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">a</span><span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:hover</span>,
<span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> > <span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.active</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">a</span><span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:focus</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">color</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-hexcolor" style="box-sizing: border-box;">#fff</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">text-decoration</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> none</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">background-color</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-hexcolor" style="box-sizing: border-box;">#428bca</span></span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">outline</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">0</span></span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span>
<span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> > <span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.disabled</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">a</span>,
<span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> > <span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.disabled</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">a</span><span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:hover</span>,
<span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> > <span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.disabled</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">a</span><span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:focus</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">color</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-hexcolor" style="box-sizing: border-box;">#999</span></span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span>
<span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> > <span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.disabled</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">a</span><span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:hover</span>,
<span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.dropdown-menu</span> > <span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.disabled</span> > <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">a</span><span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:focus</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">text-decoration</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> none</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">cursor</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> not-allowed</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">background-color</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> transparent</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">background-image</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> none</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">filter</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> progid:DXImageTransform.Microsoft.<span class="hljs-function" style="box-sizing: border-box;">gradient(enabled = false)</span></span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code>