Bootstrap 4 导航下拉菜单溢出窗口

Question

我在下面给出了navbardropdown 的示例。当我单击下拉菜单时，菜单会向右溢出，导致窗口中出现水平滚动。

即使在移动视图中，我如何才能始终将下拉菜单保留在窗口中？

<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 id="navbar-example2" class="navbar navbar-light bg-light">
  <a class="navbar-brand" href="#">Navbar</a>
  <ul class="nav nav-pills">

    <li class="nav-item dropdown">
      <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-haspopup="true" aria-expanded="false">Dropdown</a>
      <div class="dropdown-menu">
        <a class="dropdown-item" href="#one">one</a>
        <a class="dropdown-item" href="#two">two</a>
        <div role="separator" class="dropdown-divider"></div>
        <a class="dropdown-item" href="#three">three</a>
      </div>
    </li>
  </ul>
</nav>

Answer 1

来自 bootstrap 4 文档：

默认情况下，下拉菜单会自动 100% 定位在其父级的顶部和左侧。将 .dropdown-menu-right 添加到 .dropdown-menu 以右对齐下拉菜单。

所以，只需添加.dropdown-menu-right，菜单就会右对齐。

Answer 2

覆盖引导 CSS：

.dropdown-menu {
    right: 0 !important;
    left: auto !important;
}

它会为你工作

Answer 3

在 bootstrap4 中，需要添加“dropdown-menu-right”，例如：

  <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 dropdown-menu-right  " 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>

Answer 4

要解决您的问题，您只需将导航栏包装在 container（或 container-fluid）类中，如下所示：

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">

<nav id="navbar-example2" class="navbar navbar-light bg-light">
   <div class="container">
       <a class="navbar-brand" href="#">Navbar</a>
       <ul class="nav nav-pills">

           <li class="nav-item dropdown pr-3 pr-sm-2">
               <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-haspopup="true" aria-expanded="false">Dropdown</a>
               <div class="dropdown-menu">
                   <a class="dropdown-item" href="#one">one</a>
                   <a class="dropdown-item" href="#two">two</a>
                   <div role="separator" class="dropdown-divider"></div>
                   <a class="dropdown-item" href="#three">three</a>
               </div>
           </li>
       </ul>
   </div>
</nav>

<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>

此外，pr-3 pr-sm-2 类在下拉列表中添加了一点“向右填充”。