这是来自Bootstrap v4 Alpha blog theme。我将其用于项目。然后我尝试正常添加一个下拉菜单到这个导航栏，但导航栏下拉列表没有来，也没有显示。
这是下拉列表，我试图添加到此导航中。但它不起作用。这是我必须改变自定义样式的东西吗？任何意见都将不胜感激。
<li class="dropdown">
<a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span class="caret"></span></a>
<ul class="dropdown-menu">
<li><a href="#">About</a></li>
<li><a href="#">Team</a></li>
<li class="dropdown-header">Nav header</li>
<li><a href="#">Separated link</a></li>
<li><a href="#">One more separated link</a></li>
</ul>
</li>
/*
* Globals
*/
@media (min-width: 48em) {
html {
font-size: 18px;
}
}
body {
font-family: Georgia, "Times New Roman", Times, serif;
color: #555;
}
h1, .h1,
h2, .h2,
h3, .h3,
h4, .h4,
h5, .h5,
h6, .h6 {
font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
font-weight: normal;
color: #333;
}
/*
* Override Bootstrap's default container.
*/
.container {
max-width: 60rem;
}
/*
* Masthead for nav
*/
.blog-masthead {
margin-bottom: 3rem;
background-color: #428bca;
-webkit-box-shadow: inset 0 -.1rem .25rem rgba(0,0,0,.1);
box-shadow: inset 0 -.1rem .25rem rgba(0,0,0,.1);
}
/* Nav links */
.nav-link {
position: relative;
padding: 1rem;
font-weight: 500;
color: #cdddeb;
}
.nav-link:hover,
.nav-link:focus {
color: #fff;
background-color: transparent;
}
/* Active state gets a caret at the bottom */
.nav-link.active {
color: #fff;
}
.nav-link.active:after {
position: absolute;
bottom: 0;
left: 50%;
width: 0;
height: 0;
margin-left: -.3rem;
vertical-align: middle;
content: "";
border-right: .3rem solid transparent;
border-bottom: .3rem solid;
border-left: .3rem solid transparent;
}
/*
* Blog name and description
*/
.blog-header {
padding-bottom: 1.25rem;
margin-bottom: 2rem;
border-bottom: .05rem solid #eee;
}
.blog-title {
margin-bottom: 0;
font-size: 2rem;
font-weight: normal;
}
.blog-description {
font-size: 1.1rem;
color: #999;
}
@media (min-width: 40em) {
.blog-title {
font-size: 3.5rem;
}
}
/*
* Main column and sidebar layout
*/
/* Sidebar modules for boxing content */
.sidebar-module {
padding: 1rem;
/*margin: 0 -1rem 1rem;*/
}
.sidebar-module-inset {
padding: 1rem;
background-color: #f5f5f5;
border-radius: .25rem;
}
.sidebar-module-inset p:last-child,
.sidebar-module-inset ul:last-child,
.sidebar-module-inset ol:last-child {
margin-bottom: 0;
}
/* Pagination */
.blog-pagination {
margin-bottom: 4rem;
}
.blog-pagination > .btn {
border-radius: 2rem;
}
/*
* Blog posts
*/
.blog-post {
margin-bottom: 4rem;
}
.blog-post-title {
margin-bottom: .25rem;
font-size: 2.5rem;
}
.blog-post-meta {
margin-bottom: 1.25rem;
color: #999;
}
/*
* Footer
*/
.blog-footer {
padding: 2.5rem 0;
color: #999;
text-align: center;
background-color: #f9f9f9;
border-top: .05rem solid #e5e5e5;
}
.blog-footer p:last-child {
margin-bottom: 0;
}<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<meta name="description" content="">
<meta name="author" content="">
<link rel="icon" href="../../favicon.ico">
<title>Blog Template for Bootstrap</title>
<link rel="canonical" href="https://getbootstrap.com/docs/4.0/examples/blog/">
<!-- Bootstrap core CSS -->
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet">
<!-- Custom styles for this template -->
<link href="blog.css" rel="stylesheet">
</head>
<body>
<div class="blog-masthead">
<div class="container">
<nav class="nav blog-nav">
<a class="nav-link active" href="#">Home</a>
<a class="nav-link" href="#">New features</a>
<a class="nav-link" href="#">Press</a>
<a class="nav-link" href="#">New hires</a>
<a class="nav-link" href="#">About</a>
</nav>
</div>
</div>
<div class="blog-header">
<div class="container">
<h1 class="blog-title">The Bootstrap Blog</h1>
<p class="lead blog-description">An example blog template built with Bootstrap.</p>
</div>
</div>
<div class="container">
<div class="row">
<div class="col-sm-8 blog-main">
答案 0 :(得分：1)
这就是Bootstrap 4中的下拉列表（注意：这是Bootstrap 4发行版; alpha版本已过时）：
<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>
您的代码中缺少dropdown-item个类。
这是Bootstrap 4的完整导航栏示例，包括下拉列表：
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
<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>
<nav class="navbar navbar-expand-lg navbar-light bg-light">
<a class="navbar-brand" href="#">Navbar</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>
<form class="form-inline my-2 my-lg-0">
<input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">
<button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
</form>
</div>
</nav>
参考：