下拉菜单显示在父 div 后面

Question

我有一个包装器 div，在该 div 里面有一些带有下拉菜单的按钮，包装器应该有一个最大高度和一个自动滚动。

问题是如果我点击一个按钮，现在下拉总是会放在包装器后面，有没有办法让下拉器放在包装器的顶部

jsbin link

.bs-example
{
  display: flex;
  flex-direction: column;
    margin: 30px;
    max-height: 100px;
    border: 1px solid #F00;
    overflow: auto;
}

<link href="http://netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<script src="http://netdna.bootstrapcdn.com/bootstrap/3.0.0/js/bootstrap.min.js"></script>

<div class="bs-example">
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
    </div>

Answer 1

这里有一个工作的sn-p

.bs-example
{
  display: flex;
  flex-direction: column;
    margin: 30px;
    max-height: 100px;
    border: 1px solid #F00;
    overflow: auto;
}
.dropdown-menu {
    position: fixed !important;
    top: auto !important;
}

<link href="http://netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="http://netdna.bootstrapcdn.com/bootstrap/3.0.0/js/bootstrap.min.js"></script>
<div class="bs-example">
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
      <div class="btn-group">
        <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">Default <span class="caret"></span></button>
        <ul class="dropdown-menu" role="menu">
          <li><a href="#">Action</a></li>
          <li><a href="#">Another action</a></li>
          <li><a href="#">Something else here</a></li>
          <li class="divider"></li>
          <li><a href="#">Separated link</a></li>
        </ul>
      </div>
    </div>

你也可以设置left 对齐到 div 的左边，我也使用!important; 来覆盖引导默认样式。