Bootstrap4 下拉菜单

下拉菜单是可触发的,以列表格式显示链接的上下文菜单。在Bootstrap4，实现下拉菜单还是相对比较容易的。

基础下拉菜单创建

.dropdown 类用来指定一个下拉菜单。

我们可以使用一个按钮或链接来打开下拉菜单，按钮或链接需要添加 .dropdown-toggle 和 data-toggle="dropdown" 属性。

class to a <div> 元素上添加 .dropdown-menu 类来设置实际下拉菜单，然后在下拉菜单的选项中添加 .dropdown-item 类。

实例：

<!DOCTYPE html>
<html>
<head>
  <title>Bootstrap4 实例</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
  <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
  <script src="https://cdn.bootcss.com/popper.js/1.12.5/umd/popper.min.js"></script>
  <script src="https://cdn.bootcss.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
  <h2>下拉菜单</h2>
  <p>.dropdown 类用来指定一个下拉菜单。</p>
  <p>.dropdown-menu 类来设置实际下拉菜单。</p>
  <p>我们可以使用一个按钮或链接来打开下拉菜单， 按钮或链接需要添加 .dropdown-toggle 和 data-toggle="dropdown" 属性。</p>                                          
  <div class="dropdown">
    <button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
      Dropdown button
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
      <a class="dropdown-item" href="#">Link 3</a>
    </div>
  </div>
</div>
</body>
</html>

下拉菜单中的分割线

.dropdown-divider 类用于在下拉菜单中创建一个水平的分割线：

<!DOCTYPE html>
<html>
<head>
  <title>Bootstrap4 实例</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
  <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
  <script src="https://cdn.bootcss.com/popper.js/1.12.5/umd/popper.min.js"></script>
  <script src="https://cdn.bootcss.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
  <h2>下拉菜单中</h2>
  <p>.dropdown-divider 类用于在下拉菜单中创建一个水平的分割线：</p>
  <div class="dropdown">
    <button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
      Dropdown button
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
      <a class="dropdown-item" href="#">Link 3</a>
      <div class="dropdown-divider"></div>
      <a class="dropdown-item" href="#">Another link</a>
    </div>
  </div>
</div>
</body>
</html>

下拉菜单中的标题

.dropdown-header 类用于在下拉菜单中添加标题：

<!DOCTYPE html>
<html>
<head>
  <title>Bootstrap4 实例</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
  <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
  <script src="https://cdn.bootcss.com/popper.js/1.12.5/umd/popper.min.js"></script>
  <script src="https://cdn.bootcss.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
  <h2>下拉菜单中</h2>
  <p>.dropdown-header 类用于在下拉菜单中添加标题：</p>
  <div class="dropdown">
    <button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
      Dropdown button
    </button>
    <div class="dropdown-menu">
      <h5 class="dropdown-header">Dropdown header</h5>
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
      <a class="dropdown-item" href="#">Link 3</a>
      <h5 class="dropdown-header">Dropdown header</h5>
      <a class="dropdown-item" href="#">Another link</a>
    </div>
  </div>
</div>
</body>
</html>

下拉菜单中的可用项与禁用项

.active 类会让下拉菜单的选项高亮显示 (添加蓝色背景)。

如果要禁用下拉菜单的选项，可以使用.disabled 类。

<!DOCTYPE html>
<html>
<head>
  <title>Bootstrap4 实例</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
  <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
  <script src="https://cdn.bootcss.com/popper.js/1.12.5/umd/popper.min.js"></script>
  <script src="https://cdn.bootcss.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
  <h2>下拉菜单</h2>
  <p>.active 类会让下拉菜单的选项高亮显示 (添加蓝色背景)。</p>
  <p>如果要禁用下拉菜单的选项，可以使用.disabled 类。</p>
  <div class="dropdown">
    <button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
      Dropdown button
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Normal</a>
      <a class="dropdown-item active" href="#">Active</a>
      <a class="dropdown-item disabled" href="#">Disabled</a>
    </div>
  </div>
</div>
</body>
</html>

下拉菜单的定位

如果我们想让下拉菜单右对齐，可以在元素上的 .dropdown-menu 类后添加 .dropdown-menu-right 类。

<!DOCTYPE html>
<html>
<head>
  <title>Bootstrap4 实例</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
  <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
  <script src="https://cdn.bootcss.com/popper.js/1.12.5/umd/popper.min.js"></script>
  <script src="https://cdn.bootcss.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
  <h2>下拉菜单</h2>
  <p>如果我们想让下拉菜单右对齐，可以在元素上的 .dropdown-menu 类后添加 .dropdown-menu-right 类。</p>
  <div class="dropdown">
    <button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
      Dropdown button
    </button>
    <div class="dropdown-menu dropdown-menu-right">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
      <a class="dropdown-item" href="#">Link 3</a>
    </div>
  </div>
</div>
</body>
</html>

指定向上弹出的下拉菜单

如果你希望下拉菜单向上弹出，可以将 <div> 元素的 class="dropdown" 替换为 "dropup":

<!DOCTYPE html>
<html>
<head>
  <title>Bootstrap4 实例</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
  <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
  <script src="https://cdn.bootcss.com/popper.js/1.12.5/umd/popper.min.js"></script>
  <script src="https://cdn.bootcss.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
  <h2>下拉菜单</h2>
  <p> .dropup 类用于设置下拉菜单向上弹出：</p><br>
  <div class="dropup">
    <button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
      Dropdown button
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
    </div>
  </div>
</div>
</body>
</html>

按钮中设置下拉菜单

我们可以在按钮中添加下拉菜单：

<!DOCTYPE html>
<html>
<head>
  <title>Bootstrap4 实例</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.1.0/css/bootstrap.min.css">
  <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
  <script src="https://cdn.bootcss.com/popper.js/1.12.5/umd/popper.min.js"></script>
  <script src="https://cdn.bootcss.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
  <h2>按钮中的下拉菜单</h2>
  <div class="btn-group">
    <button type="button" class="btn btn-primary">Primary</button>
    <button type="button" class="btn btn-primary dropdown-toggle dropdown-toggle-split" data-toggle="dropdown">
      <span class="caret"></span>
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
    </div>
  </div>
  <div class="btn-group">
    <button type="button" class="btn btn-secondary">Secondary</button>
    <button type="button" class="btn btn-secondary dropdown-toggle dropdown-toggle-split" data-toggle="dropdown">
      <span class="caret"></span>
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
    </div>
  </div>
  <div class="btn-group">
    <button type="button" class="btn btn-success">Success</button>
    <button type="button" class="btn btn-success dropdown-toggle dropdown-toggle-split" data-toggle="dropdown">
      <span class="caret"></span>
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
    </div>
  </div>
  <div class="btn-group">
    <button type="button" class="btn btn-info">Info</button>
    <button type="button" class="btn btn-info dropdown-toggle dropdown-toggle-split" data-toggle="dropdown">
      <span class="caret"></span>
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
    </div>
  </div>
  <div class="btn-group">
    <button type="button" class="btn btn-warning">Warning</button>
    <button type="button" class="btn btn-warning dropdown-toggle dropdown-toggle-split" data-toggle="dropdown">
      <span class="caret"></span>
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
    </div>
  </div>
  <div class="btn-group">
    <button type="button" class="btn btn-danger">Danger</button>
    <button type="button" class="btn btn-danger dropdown-toggle dropdown-toggle-split" data-toggle="dropdown">
      <span class="caret"></span>
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
    </div>
  </div>
</div>
</body>
</html>

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Bootstrap4 下拉菜单