下降（Drop downs）

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2023-12-01

本章将重点介绍Bootstrap下拉菜单。下拉菜单是可切换的上下文菜单，用于以列表格式显示链接。这可以通过下拉JavaScript插件进行交互。

要使用下拉列表，只需将下拉菜单包装在类.dropdown 。以下示例演示了一个基本的下拉菜单 -

<div class = "dropdown">
   <button type = "button" class = "btn dropdown-toggle" id = "dropdownMenu1" data-toggle = "dropdown">
      Topics
      <span class = "caret"></span>
   </button>
   <ul class = "dropdown-menu" role = "menu" aria-labelledby = "dropdownMenu1">
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">Java</a>
      </li>
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">Data Mining</a>
      </li>
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">
            Data Communication/Networking
         </a>
      </li>
      <li role = "presentation" class = "divider"></li>
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">Separated link</a>
      </li>
   </ul>
</div>

选项 (Options)

对齐(Alignment)

通过将.pull-right类添加到.dropdown-menu将下拉菜单右对齐。以下示例演示了这一点 -

<div class = "dropdown">
   <button type = "button" class = "btn dropdown-toggle" id = "dropdownMenu1" data-toggle = "dropdown">
      Topics
      <span class = "caret"></span>
   </button>
   <ul class = "dropdown-menu pull-right" role = "menu" aria-labelledby = "dropdownMenu1">
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">Java</a>
      </li>
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">Data Mining</a>
      </li>
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">
            Data Communication/Networking
         </a>
      </li>
      <li role = "presentation" class = "divider"></li>
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">Separated link</a>
      </li>
   </ul>
</div>

Headers

您可以使用class dropdown-header在任何下拉菜单中添加标题以标记操作的各个部分。以下示例演示了这一点 -

<div class = "dropdown">
   <button type = "button" class = "btn dropdown-toggle" id = "dropdownMenu1" data-toggle = "dropdown">
      Topics
      <span class = "caret"></span>
   </button>
   <ul class = "dropdown-menu" role = "menu" aria-labelledby = "dropdownMenu1">
      <li role = "presentation" class = "dropdown-header">Dropdown header</li>
      <li role = "presentation" >
         <a role = "menuitem" tabindex = "-1" href = "#">Java</a>
      </li>
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">Data Mining</a>
      </li>
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">
            Data Communication/Networking
         </a>
      </li>
      <li role = "presentation" class = "divider"></li>
      <li role = "presentation" class = "dropdown-header">Dropdown header</li>
      <li role = "presentation">
         <a role = "menuitem" tabindex = "-1" href = "#">Separated link</a>
      </li>
   </ul>
</div>