Question

似乎是一个简单的问题，很可能我缺少明显的东西。

我有一个卡片布局，里面有一系列文本/按钮/列表。这些按钮之一是下拉菜单，由于某种原因，下拉菜单不会“下拉”。这段代码是直接从bootstrap 4's site on dropdown menu buttons复制的，但按钮类的样式（大纲大纲）除外。

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet"/>
      <button class="btn btn-outline-primary dropdown-toggle" type="button" id="dropdownMenu2" data-toggle="dropdown"
        aria-haspopup="true" aria-expanded="false">
        Dropdown
      </button>
      <div class="dropdown-menu" aria-labelledby="dropdownMenu2">
        <button class="dropdown-item" type="button">Action</button>
        <button class="dropdown-item" type="button">Another action</button>
        <button class="dropdown-item" type="button">Something else here</button>
      </div>

Answer 1

您必须包括Bootstrap JS。

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">

<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
        
         <button class="btn btn-outline-primary dropdown-toggle" type="button" id="dropdownMenu2" data-toggle="dropdown"
            aria-haspopup="true" aria-expanded="false">
            Dropdown
          </button>
          <div class="dropdown-menu" aria-labelledby="dropdownMenu2">
            <button class="dropdown-item" type="button">Action</button>
            <button class="dropdown-item" type="button">Another action</button>
            <button class="dropdown-item" type="button">Something else here</button>
          </div>

请参考以下链接：https://getbootstrap.com/docs/4.0/getting-started/introduction/

Answer 2

是否包含所有的js文件？ jQuery，Popper和Bootstrap？

<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">
<button class="btn btn-outline-primary dropdown-toggle" type="button" id="dropdownMenu2" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
        Dropdown
      </button>
<div class="dropdown-menu" aria-labelledby="dropdownMenu2">
  <button class="dropdown-item" type="button">Action</button>
  <button class="dropdown-item" type="button">Another action</button>
  <button class="dropdown-item" type="button">Something else here</button>
</div>
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>

Bootstrap 4下拉按钮不会下降

2 个答案: