问题
I'm newbie to css and bootstrap and can not figure out how to solve this. Any help are welcome.
I have two problems with my code.
1) When I click on the 'Welcome, User' menu in small screens (mobile), the dropdown menu opens inside the navigation bar, distorting the bar and changing its height. I want it to behave in the same way as on larger screens (desktops, for example). When I click, I want it to open the menu items without changing the navigation bar, in front of the navigation bar but not inside.
2) Another problem: even on larger screens, I can not see the menu items completely. Some of the text of the items is hidden at the edge of the screen. I would like the menu to appear completely on the screen, no matter if it is desktop or mobile.
To make it clear, I record a very small video demonstrating the problem: https://puu.sh/Bq34w/ac56908be0.mp4
The complete code: https://jsfiddle.net/fredslz/0v7qwjdm/12/
<!doctype html>
<html lang="en">
<body class="text-center">
<nav class="navbar navbar-expand-md navbar-light fixed-top" style="background-color: #FFFFFF;">
<button class="navbar-toggler navbar-nav mr-auto" type="button" data-toggle="collapse" data-target="#navbarCollapse" aria-controls="navbarCollapse" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<a class="navbar-brand mx-auto" href="#">My Brand</a>
<ul class="nav navbar-nav ml-md--auto">
<li class="dropdown">
<a href="#" class="nav-link dropdown-toggle" id="navbarDropdown" data-toggle="dropdown" aria-expanded="false">
Welcome, User <b class="caret"></b>
</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>
</nav>
</body>
</html>
And the CSS:
.navbar {
-webkit-box-shadow: 0 8px 6px -6px #999;
-moz-box-shadow: 0 8px 6px -6px #999;
box-shadow: 0 8px 6px -6px #999;
}
回答1:
You need to use dropdown-menu-right on the dropdown if you want the menu items properly aligned.
What's not clear is why you're using the toggler, because you don't have any collapsible menu items (navbar-collapse). Just remove the toggler and use navbar-expand so that the Navbar doesn't collapse in the mobile view.
<nav class="navbar navbar-expand navbar-light fixed-top" style="background-color: #FFFFFF;">
<a class="navbar-brand mx-auto" href="#">My Brand</a>
<ul class="nav navbar-nav">
<li class="dropdown">
<a href="#" class="nav-link dropdown-toggle" id="navbarDropdown" data-toggle="dropdown" aria-expanded="false">
Welcome, User <b class="caret"></b>
</a>
<div class="dropdown-menu dropdown-menu-right">
<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>
</nav>
https://www.codeply.com/go/j1HZLEdyrC
The dropdown will always open inside the mobile collapsed Navbar which is by-design. If you do want to keep the mobile toggler, and intend to add collapsible items, you can use position-absolute on the dropdown-menu to override the default behavior.
<nav class="navbar navbar-expand-md navbar-light" style="background-color: #FFFFFF;">
<button class="navbar-toggler navbar-nav mr-auto" type="button" data-toggle="collapse" data-target="#navbarCollapse" aria-controls="navbarCollapse" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<a class="navbar-brand mx-auto" href="#">My Brand</a>
<ul class="nav navbar-nav">
<li class="dropdown">
<a href="#" class="nav-link dropdown-toggle" id="navbarDropdown" data-toggle="dropdown" aria-expanded="false">
Welcome, User <b class="caret"></b>
</a>
<div class="dropdown-menu dropdown-menu-right position-absolute" 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>
</nav>
Demo of both options: https://www.codeply.com/go/j1HZLEdyrC
Related: Bootstrap 4 Navbar Dropdown Menu Items Right
回答2:
For the issue with the mobile dropdown, you can use this to position it absolutely in the mobile view too:
.navbar-nav .dropdown-menu {
position: absolute;
}
For the alignment of the dropdown, just add the class dropdown-menu-right to your dropdown-menu.
See demo below (I have given !important to cope with the cascading order in the snippet) and working fiddle here:
.navbar {
-webkit-box-shadow: 0 8px 6px -6px #999;
-moz-box-shadow: 0 8px 6px -6px #999;
box-shadow: 0 8px 6px -6px #999;
/* the rest of your styling */
}
.navbar-nav .dropdown-menu {
position: absolute !important;
}<script type="text/javascript" src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js"></script>
<link rel="stylesheet" type="text/css" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css">
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"></script>
<script type="text/javascript" src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js"></script>
<nav class="navbar navbar-expand-md navbar-light fixed-top" style="background-color: #FFFFFF;">
<button class="navbar-toggler navbar-nav mr-auto" type="button" data-toggle="collapse" data-target="#navbarCollapse" aria-controls="navbarCollapse" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<a class="navbar-brand mx-auto" href="#">My Brand</a>
<ul class="nav navbar-nav ml-md--auto">
<li class="dropdown">
<a href="#" class="nav-link dropdown-toggle" id="navbarDropdown" data-toggle="dropdown" aria-expanded="false">
Welcome, User <b class="caret"></b>
</a>
<div class="dropdown-menu dropdown-menu-right" aria-labelledby="navbarDropdown">
<!-- ADDED CLASS -->
<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>
</nav>来源：https://stackoverflow.com/questions/52184565/bootstrap-4-dropdown-menu-navbar-user-preferences-welcome-user