Bootstrap学习笔记（四）-----下拉菜单

一、基本用法

<div class="dropdown">
  <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown">
    下拉菜单
    <span class="caret"></span>
  </button>
  <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
  </ul>
</div>

效果如下图所示：

1.1 使用方法：

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:

<div class="dropdown"></div>

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:

data-toggle="dropdown"

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:

<ul class="dropdown-menu">

1.2 原理分析：

ul的类dropdown-menu有个属性为display: none; 当点击显示ul时，给最外层div添加了个open的类；再次点击取消.open

.open > .dropdown-menu {
  display: block;
}

 

二、下拉菜单分隔符

<li role="presentation" class="divider">

<div class="dropdown">
  <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown">
    食物
    <span class="caret"></span>
  </button>
  <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">苹果</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">香蕉</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">梨</a></li>
    <li role="presentation" class="divider">   //分隔符
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">萝卜</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">茄子</a></li>
  </ul>
</div> 

效果如下：

三、下拉菜单的菜单标题

<li role="presentation" class="dropdown-header">第二部分菜单头部</li>

<div class="dropdown">
  <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown">
    下拉菜单
    <span class="caret"></span>
  </button>
  <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
    <li role="presentation" class="dropdown-header">第一部分菜单头部</li>  //菜单头部
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation" class="divider"></li>
    <li role="presentation" class="dropdown-header">第二部分菜单头部</li>  //菜单头部
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
  </ul>
</div> 

四、下拉菜单的对齐方式

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：

<h4>使用pull-right类使下拉菜单与父容器右边对齐</h4>
 <div class="dropdown">
  <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown">
    下拉菜单
    <span class="caret"></span>
  </button>
  <ul class="dropdown-menu pull-right" role="menu" aria-labelledby="dropdownMenu1">            //pull-right
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation" class="divider"></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
  </ul>
</div>
<br />
<br />
<h4>使用dropdown-menu-right类使下拉菜单与父容器右边对齐</h4>
<div class="dropdown">
  <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown">
    下拉菜单
    <span class="caret"></span>
  </button>
  <ul class="dropdown-menu dropdown-menu-right" role="menu" aria-labelledby="dropdownMenu1">       //dropdown-menu-right
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation" class="divider"></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
  </ul>
</div> 

五、下拉菜单的状态

当前状态（.active）和禁用状态（.disabled）

<div class="dropdown">
  <button class="btn btn-default dropdown-toggle" type="button" id="dropdownMenu1" data-toggle="dropdown">
    下拉菜单
    <span class="caret"></span>
  </button>
  <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
    <li role="presentation" class="active"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>   //当前状态
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>
    <li role="presentation" class="divider"></li>
    <li role="presentation" class="disabled"><a role="menuitem" tabindex="-1" href="#">下拉菜单项</a></li>   //禁用状态
  </ul>
</div>