本文介绍了缺少引导下拉子菜单的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
Bootstrap 3 仍在 RC 中，但我只是在尝试实现它.我不知道如何放置子菜单类.即使在 css 中没有类，甚至新文档也没有提及它
它在 2.x 中，类名是下拉子菜单
解决方案
Bootstrap 5(2021 年更新)
添加一些 JavaScript 以防止子菜单在父下拉菜单打开时关闭.这可以通过切换 display:block...
let dropdowns = document.querySelectorAll('.dropdown-toggle')dropdowns.forEach((dd)=>{dd.addEventListener('click', function (e) {var el = this.nextElementSiblingel.style.display = el.style.display==='block'?'none':'block'})})
Bootstrap 5 多级下拉菜单 - 点击
Bootstrap 5 多级下拉菜单 - 悬停
或者，您可以将这种仅 CSS 的方法用于导航栏下拉菜单...
.dropdown-submenu {位置:相对；}.dropdown-submenu .dropdown-menu {顶部:0；左:100%；边距顶部:-1px；}.navbar-nav li:hover >ul.下拉菜单{显示:块；}
Bootstrap 5 导航栏下拉悬停子菜单(仅限 CSS)
引导程序 4(2018 年更新)
dropdown-submenu 已在 Bootstrap 3 RC 中移除.用 Bootstrap 作者 Mark Otto 的话来说......
<块引用>
"子菜单现在在网络上没有太多的位置，尤其是移动网络.它们将被 3.0" 删除.- https://github.com/twbs/bootstrap/pull/6342
但是，通过一些额外的 CSS，您可以获得相同的功能.
悬停时的导航栏子菜单:
.navbar-nav li:hover >ul.下拉菜单{显示:块；}. 下拉子菜单 {位置:相对；}.dropdown-submenu>.dropdown-menu {顶部:0；左:100%；边距顶部:-6px；}
导航栏子菜单下拉悬停
导航栏子菜单下拉悬停(右对齐)
导航栏子菜单下拉点击(右对齐)
导航栏下拉悬停(无子菜单)
<小时>
引导程序 3
这是一个使用 3.0 RC 1 的示例:http://bootply.com/71520
以下是使用 Bootstrap 3.0.0(最终版)的示例:http://bootply.com/86684
CSS
.dropdown-submenu {位置:相对；}.dropdown-submenu>.dropdown-menu {顶部:0；左:100%；边距顶部:-6px；左边距:-1px；-webkit-border-radius:0 6px 6px 6px;-moz-border-radius:0 6px 6px 6px;边框半径:0 6px 6px 6px；}.dropdown-submenu:hover>.dropdown-menu {显示:块；}.dropdown-submenu>a:after {显示:块；内容:"";浮动:对；宽度:0；高度:0；边框颜色:透明；边框样式:实心；边框宽度:5px 0 5px 5px；左边框颜色:#cccccc；边距顶部:5px；右边距:-10px；}.dropdown-submenu:hover>a:after {左边框颜色:#ffffff；}.dropdown-submenu.pull-left {浮动:无；}.dropdown-submenu.pull-left>.dropdown-menu {左:-100%；左边距:10px；-webkit-border-radius:6px 0 6px 6px;-moz-边框半径:6px 0 6px 6px；边框半径:6px 0 6px 6px；}
示例标记
附:- 导航栏中调整左侧位置的示例:http://bootply.com/92442
Bootstrap 3 is still at RC, but I was just trying to implement it. I couldn't figure out how to put a sub menu class. Even there is no class in css and even the new docs don't say anything about it
It was there in 2.x with class name as dropdown-submenu
解决方案
Bootstrap 5 (update 2021)
Add some JavaScript to prevent the submenu from closing when the parent dropdown is open. This can be done be toggle display:block...
let dropdowns = document.querySelectorAll('.dropdown-toggle')
dropdowns.forEach((dd)=>{
dd.addEventListener('click', function (e) {
var el = this.nextElementSibling
el.style.display = el.style.display==='block'?'none':'block'
})
})
Bootstrap 5 Multi-level Dropdown - click
Bootstrap 5 Multi-level Dropdown - hover
Or, you can use this CSS only method for Navbar dropdowns...
.dropdown-submenu {
position: relative;
}
.dropdown-submenu .dropdown-menu {
top: 0;
left: 100%;
margin-top: -1px;
}
.navbar-nav li:hover > ul.dropdown-menu {
display: block;
}
Bootstrap 5 Navbar Dropdown Hover Submenus (CSS only)
Bootstrap 4 (update 2018)
The dropdown-submenu has been removed in Bootstrap 3 RC. In the words of Bootstrap author Mark Otto..
"Submenus just don't have much of a place on the web right now, especially the mobile web. They will be removed with 3.0" - https://github.com/twbs/bootstrap/pull/6342
But, with a little extra CSS you can get the same functionality.
navbar submenu on hover:
.navbar-nav li:hover > ul.dropdown-menu {
display: block;
}
.dropdown-submenu {
position:relative;
}
.dropdown-submenu>.dropdown-menu {
top:0;
left:100%;
margin-top:-6px;
}
Navbar submenu dropdown hover
Navbar submenu dropdown hover (right aligned)
Navbar submenu dropdown click (right aligned)
Navbar dropdown hover (no submenu)
Bootstrap 3
Here is an example that uses 3.0 RC 1: http://bootply.com/71520
Here is an example that uses Bootstrap 3.0.0 (final): http://bootply.com/86684
CSS
.dropdown-submenu {
position:relative;
}
.dropdown-submenu>.dropdown-menu {
top:0;
left:100%;
margin-top:-6px;
margin-left:-1px;
-webkit-border-radius:0 6px 6px 6px;
-moz-border-radius:0 6px 6px 6px;
border-radius:0 6px 6px 6px;
}
.dropdown-submenu:hover>.dropdown-menu {
display:block;
}
.dropdown-submenu>a:after {
display:block;
content:" ";
float:right;
width:0;
height:0;
border-color:transparent;
border-style:solid;
border-width:5px 0 5px 5px;
border-left-color:#cccccc;
margin-top:5px;
margin-right:-10px;
}
.dropdown-submenu:hover>a:after {
border-left-color:#ffffff;
}
.dropdown-submenu.pull-left {
float:none;
}
.dropdown-submenu.pull-left>.dropdown-menu {
left:-100%;
margin-left:10px;
-webkit-border-radius:6px 0 6px 6px;
-moz-border-radius:6px 0 6px 6px;
border-radius:6px 0 6px 6px;
}
Sample Markup
<div class="navbar navbar-default navbar-fixed-top" role="navigation">
<div class="container">
<div class="navbar-header">
<button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-ex1-collapse">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
</div>
<div class="collapse navbar-collapse navbar-ex1-collapse">
<ul class="nav navbar-nav">
<li class="menu-item dropdown">
<a href="#" class="dropdown-toggle" data-toggle="dropdown">Drop Down<b class="caret"></b></a>
<ul class="dropdown-menu">
<li class="menu-item dropdown dropdown-submenu">
<a href="#" class="dropdown-toggle" data-toggle="dropdown">Level 1</a>
<ul class="dropdown-menu">
<li class="menu-item ">
<a href="#">Link 1</a>
</li>
<li class="menu-item dropdown dropdown-submenu">
<a href="#" class="dropdown-toggle" data-toggle="dropdown">Level 2</a>
<ul class="dropdown-menu">
<li>
<a href="#">Link 3</a>
</li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
</div>
</div>
P.S. - Example in navbar that adjusts left position: http://bootply.com/92442
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