小贝子编程

如何在Boostrap 4的下拉菜单上放置动画



有一个关于导航栏切换器折叠的动画：

<!doctype html>
<html lang="en">
<head>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Bootstrap CSS -->
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">
<title>Hello, world!</title>
</head>
<body>
<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>
<!-- Optional JavaScript -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js" integrity="sha384-ZMP7rVo3mIykV+2+9J3UJ46jBk0WLaUAdn689aCwoqbBJiSnjAK/l8WvCWPIPm49" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js" integrity="sha384-ChfqqxuZUCnJSK3+MXmPNIyE6ZbWh2IMqE241rYiqJxyMiZ6OW/JmZQ5stwEULTy" crossorigin="anonymous"></script>
</body>
</html>

如何使用下拉菜单执行相同的操作？

我一直在谷歌上搜索这个，我在Stackoverflow上找到了一些答案，但这些脚本在这里不起作用。也许是因为他们使用了必需的图书馆，但我没有找到任何东西。

您可以在下拉菜单中添加一个过渡，并在 css 上使用以下代码：

.dropdown .dropdown-menu {
-webkit-transition: max-height 0.3s, opacity 0.2s 0.1s, visibility 0s 4s;
-moz-transition: max-height 0.3s, opacity 0.2s 0.1s, visibility 0s 4s;
-ms-transition: max-height 0.3s, opacity 0.2s 0.1s, visibility 0s 4s;
-o-transition: max-height 0.3s, opacity 0.2s 0.1s, visibility 0s 4s;
transition: max-height 0.3s, opacity 0.2s 0.1s, visibility 0s 4s;
max-height: 0;
display: block;
overflow: hidden;
opacity: 0;
visibility: hidden;
}
.dropdown.show .dropdown-menu {
-webkit-transition: max-height 0.3s, opacity 0.2s, visibility 0s;
-moz-transition: max-height 0.3s, opacity 0.2s, visibility 0s;
-ms-transition: max-height 0.3s, opacity 0.2s, visibility 0s;
-o-transition: max-height 0.3s, opacity 0.2s, visibility 0s;
transition: max-height 0.3s, opacity 0.2s, visibility 0s;
max-height: 190px;
opacity: 1;
visibility: visible;
}

下面是一个工作示例：

.dropdown .dropdown-menu {
-webkit-transition: max-height 0.3s, opacity 0.2s 0.1s, visibility 0s 4s;
-moz-transition: max-height 0.3s, opacity 0.2s 0.1s, visibility 0s 4s;
-ms-transition: max-height 0.3s, opacity 0.2s 0.1s, visibility 0s 4s;
-o-transition: max-height 0.3s, opacity 0.2s 0.1s, visibility 0s 4s;
transition: max-height 0.3s, opacity 0.2s 0.1s, visibility 0s 4s;
max-height: 0;
display: block;
overflow: hidden;
opacity: 0;
visibility: hidden;
}
.dropdown.show .dropdown-menu {
-webkit-transition: max-height 0.3s, opacity 0.2s, visibility 0s;
-moz-transition: max-height 0.3s, opacity 0.2s, visibility 0s;
-ms-transition: max-height 0.3s, opacity 0.2s, visibility 0s;
-o-transition: max-height 0.3s, opacity 0.2s, visibility 0s;
transition: max-height 0.3s, opacity 0.2s, visibility 0s;
max-height: 190px;
opacity: 1;
visibility: visible;
}
<!doctype html>
<html lang="en">
<head>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Bootstrap CSS -->
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">
<title>Hello, world!</title>
</head>
<body>
<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>
<!-- Optional JavaScript -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js" integrity="sha384-ZMP7rVo3mIykV+2+9J3UJ46jBk0WLaUAdn689aCwoqbBJiSnjAK/l8WvCWPIPm49" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js" integrity="sha384-ChfqqxuZUCnJSK3+MXmPNIyE6ZbWh2IMqE241rYiqJxyMiZ6OW/JmZQ5stwEULTy" crossorigin="anonymous"></script>
</body>
</html>

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