按钮下拉菜单
向按钮添加下拉菜单，只需要简单地在在一个 .btn-group 中放置按钮和下拉菜单即可
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<title>BootstrapDemo</title>
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</head>
<body style="padding: 20px;">
<div class="btn-group btn-group-lg">
<button type="button" class="btn btn-info dropdown-toggle" data-toggle = "dropdown">按钮菜单
<span class = "caret"></span>
</button>
<ul class="dropdown-menu" role = "menu">
<li role = "presentation"><a href="#">子菜单1</a></li>
<li role = "presentation"><a href="#">子菜单2</a></li>
<li role = "presentation"><a href="#">子菜单3</a></li>
<li role = "presentation"><a href="#">子菜单4</a></li>
</ul>
</div>
<div class="btn-group btn-group-lg">
<button type="button" class="btn btn-warning dropdown-toggle" data-toggle = "dropdown">按钮菜单
<span class = "caret"></span>
</button>
<ul class="dropdown-menu" role = "menu">
<li role = "presentation"><a href="#">子菜单1</a></li>
<li role = "presentation"><a href="#">子菜单2</a></li>
<li role = "presentation"><a href="#">子菜单3</a></li>
<li role = "presentation"><a href="#">子菜单4</a></li>
</ul>
</div>
</body>
</html>
此处我们未使用div class = "dropdown"，尽管dropdown也可以实现按钮下拉菜单，但是dropdown是块级显示的。而.btn-group
的display是inline-block.
效果：
分割的按钮下拉菜单
使用两个Button，一个显示内容，另一个用来显示下拉功能
<body style="padding: 20px;">
<div class="btn-group btn-group-lg">
<button type="button" class="btn btn-info">按钮菜单</button>
<button type="button" class="btn btn-info dropdown-toggle" data-toggle = "dropdown">
<span class = "caret"></span>
</button>
<ul class="dropdown-menu" role = "menu">
<li role = "presentation"><a href="#">子菜单1</a></li>
<li role = "presentation"><a href="#">子菜单2</a></li>
<li role = "presentation"><a href="#">子菜单3</a></li>
<li role = "presentation"><a href="#">子菜单4</a></li>
</ul>
</div>
<div class="btn-group btn-group-lg">
<button type="button" class="btn btn-warning">按钮菜单</button>
<button type="button" class="btn btn-warning dropdown-toggle" data-toggle = "dropdown">
<span class = "caret"></span>
</button>
<ul class="dropdown-menu" role = "menu">
<li role = "presentation"><a href="#">子菜单1</a></li>
<li role = "presentation"><a href="#">子菜单2</a></li>
<li role = "presentation"><a href="#">子菜单3</a></li>
<li role = "presentation"><a href="#">子菜单4</a></li>
</ul>
</div>
</body>
效果：
按钮上拉菜单
只需要在.btn-group容器中添加.dropup即可。
<body style="padding: 200px;">
<div class="btn-group btn-group-lg dropup">
<button type="button" class="btn btn-info">按钮菜单</button>
<button type="button" class="btn btn-info dropdown-toggle" data-toggle = "dropdown">
<span class = "caret"></span>
</button>
<ul class="dropdown-menu" role = "menu">
<li role = "presentation"><a href="#">子菜单1</a></li>
<li role = "presentation"><a href="#">子菜单2</a></li>
<li role = "presentation"><a href="#">子菜单3</a></li>
<li role = "presentation"><a href="#">子菜单4</a></li>
</ul>
</div>
<div class="btn-group btn-group-lg dropup">
<button type="button" class="btn btn-warning">按钮菜单</button>
<button type="button" class="btn btn-warning dropdown-toggle" data-toggle = "dropdown">
<span class = "caret"></span>
</button>
<ul class="dropdown-menu" role = "menu">
<li role = "presentation"><a href="#">子菜单1</a></li>
<li role = "presentation"><a href="#">子菜单2</a></li>
<li role = "presentation"><a href="#">子菜单3</a></li>
<li role = "presentation"><a href="#">子菜单4</a></li>
</ul>
</div>
</body>
