1,首先在head中引入文件
<link href="http://cdn.bootcss.com/bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet">
<script src="http://cdn.bootcss.com/jquery/2.1.4/jquery.js"></script>
<script src="http://cdn.bootcss.com/bootstrap/3.3.5/js/bootstrap.js"></script>
<script src="http://cdn.bootcss.com/bootstrap-hover-dropdown/2.0.10/bootstrap-hover-dropdown.min.js"></script>
2,然后把下面的代码复制在nav中
<div class="dropdown">
<button id="dLabel" type="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
Dropdown trigger
<span class="caret"></span>
</button>
<ul class="dropdown-menu" role="menu" aria-labelledby="dLabel">
...
</ul>
</div>
3,在butoon中的 <button id="dLabel" type="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"> 更换为
<button type="button" class="btn dropdown-toggle" id="dropdownMenu1" data-toggle="dropdown" data-hover="dropdown">