Bootstrap 4 导航栏下拉菜单不起作用

Question

我无法让 bootstrap 4 中的下拉菜单正常运行。我一直在寻找解决方案，虽然有些人找到了它们，但它们对我没有用。

我尝试使用引导文档中的模板启用下拉功能，以及使用 jquery 来在悬停时显示下拉菜单。都不工作。我已经包含了所有必要的 JS 文件。在使用 JS 显示悬停菜单之前和之后，下拉菜单都不起作用。

<nav class="navbar navbar-expand-lg  navbar-light bg-light">
  <a class="navbar-brand" href="#"><img src="assets/img/nav_logo.png" class="img-fluid"></a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>

  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item active">
        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Link</a>
      </li>
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          Dropdown
        </a>
        <div class="dropdown-menu" aria-labelledby="navbarDropdown">
          <a class="dropdown-item" href="#">Action</a>
          <a class="dropdown-item" href="#">Another action</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="#">Something else here</a>
        </div>
      </li>
      <li class="nav-item">
        <a class="nav-link disabled" href="#">Disabled</a>
      </li>
    </ul>

  </div>
</nav>

鼠标悬停下拉的JS

$('body').on('mouseenter mouseleave','.dropdown',function(e){
  var _d=$(e.target).closest('.dropdown');
  if (e.type === 'mouseenter')_d.addClass('show');
  setTimeout(function(){
    _d.toggleClass('show', _d.is(':hover'));
    $('[data-toggle="dropdown"]', _d).attr('aria-expanded',_d.is(':hover'));
  },300);
});

当前站点可以在这里找到： http://shatteredsite.com/testing/shatteredsite.html

感谢您能给我的任何帮助！

Answer 1

从您的参考代码中删除它

<link rel="stylesheet" href="assets/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">

改成这个

<link rel="stylesheet" href="assets/css/bootstrap.min.css">

这些脚本引用也是如此

<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="assets/js/bootstrap.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>

改成

<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js"></script>

<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js"></script>

<script src="assets/js/bootstrap.js"></script>

Answer 2

Bootstrap v4 具有 recently changed dropdowns，导致 previous method 在悬停时打开下拉菜单 - 您尝试过 - 不再有效。

这是 v4.1.2 及更高版本的最新解决方案：

function toggleDropdown (e) {
  let _d = $(e.target).closest('.dropdown'),
      _m = $('.dropdown-menu', _d);
  setTimeout(function(){
    let shouldOpen = e.type !== 'click' && _d.is(':hover');
    _m.toggleClass('show', shouldOpen);
    _d.toggleClass('show', shouldOpen);
    $('[data-toggle="dropdown"]', _d).attr('aria-expanded', shouldOpen);
  }, e.type === 'mouseleave' ? 300 : 0);
}

$('body')
  .on('mouseenter mouseleave','.dropdown',toggleDropdown)
  .on('click', '.dropdown-menu a', toggleDropdown);

看看它的工作原理：

function toggleDropdown (e) {
  let _d = $(e.target).closest('.dropdown'),
      _m = $('.dropdown-menu', _d);
  setTimeout(function(){
    let shouldOpen = e.type !== 'click' && _d.is(':hover');
    _m.toggleClass('show', shouldOpen);
    _d.toggleClass('show', shouldOpen);
    $('[data-toggle="dropdown"]', _d).attr('aria-expanded', shouldOpen);
  }, e.type === 'mouseleave' ? 300 : 0);
}

$('body')
  .on('mouseenter mouseleave','.dropdown',toggleDropdown)
  .on('click', '.dropdown-menu a', toggleDropdown);

/* not needed, simply prevents reload on nav links clicks */
$('nav a').on('click tap', e => e.preventDefault())

<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js"></script>

<nav class="navbar navbar-expand-lg  navbar-light bg-light">
  <a class="navbar-brand" href="#">Logo</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item active">
        <a class="nav-link" href>Home <span class="sr-only">(current)</span></a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href>Link</a>
      </li>
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          Dropdown
        </a>
        <div class="dropdown-menu" aria-labelledby="navbarDropdown">
          <a class="dropdown-item" href>Action</a>
          <a class="dropdown-item" href>Another action</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href>Something else here</a>
        </div>
      </li>
    </ul>
  </div>
</nav>