Bootstrap 4 不可折叠项目下拉正在扩展导航栏答案

【问题标题】：Boostrap 4 non collapsible items drop down is expanding the NavbarBootstrap 4 不可折叠项目下拉正在扩展导航栏
【发布时间】：2019-07-29 09:37:57
【问题描述】：

我从这个问题Bootstrap 4 - Navbar items outside the collapse 中关注了一个 sn-p，它帮助我创建了几个不可折叠的项目，用于在视口缩小时。但是，我在这些不可折叠的项目之一中有一个下拉菜单，当该项目展开时，它会扩展整个导航栏并且不会在其顶部弹出。您可以在下面的链接中的示例中看到它

http://codeply.com/go/U0GQYJd2JO

导航条码：

<nav class="navbar navbar-expand-lg fixed-top navbar-light bg-light" id="mainNav">
    <a class="navbar-brand" href="/">
        MY Site
    </a>
    <div class="d-flex flex-row order-2 order-lg-3">
        <ul class="navbar-nav flex-row">
            <li style="width:250px;">
                <select data-placeholder="Jump to site..." id="quickjump-menu" class="form-control form-control-chosen">
                    <option value=""></option>
                    <option value="/sites/site/139/">protein</option>
                    <option value="/sites/site/138/">shake</option>
                    <option value="/sites/site/159/">soup</option>
                    <option value="/sites/site/115/">test 1</option>
                    <option value="/sites/site/116/">test 2</option>
                </select>
            </li>
            <li class="nav-item dropdown">
                <a class="nav-link p-2 dropdown-toggle" data-toggle="dropdown" href="#" role="button"
                    aria-haspopup="true" aria-expanded="false">
                    <i class="fa fa-user fa-lg"></i>
                </a>
                <div class="dropdown-menu dropdown-menu-right">
                    <div class="dropdown-header text-center">
                        <strong>Admin</strong>
                    </div>
                    <a class="dropdown-item" href="/admin/" target='_blank'>
                        <i class="fa fa-user fa-fw"></i> Admin
                    </a>
                    <a class="dropdown-item" href="/user_info/">
                        <i class="fa fa-users fa-fw"></i> User Info
                    </a>
                    <div class="dropdown-header text-center">
                        <strong>Settings</strong>
                    </div>
                    <a class="dropdown-item" href="/app_settings/">
                        <i class="fa fa-gears fa-fw"></i> App Settings
                    </a>
                    <div class="dropdown-header text-center">
                        <strong>User</strong>
                    </div>
                    <a class="dropdown-item" href="/edit_profile/1/">
                        <i class="fa fa-user fa-fw"></i> User Profile
                    </a>
                    <a class="dropdown-item" href="/logout/?next=/login">
                        <i class="fa fa-gear fa-fw"></i> Log out
                    </a>
                </div>
            </li>
        </ul>
        <button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse"
            data-target="#navbarResponsive" aria-controls="navbarResponsive" aria-expanded="false"
            aria-label="Toggle navigation">
            <span class="navbar-toggler-icon"></span>
        </button>
    </div>
    <div class="collapse navbar-collapse" id="navbarResponsive">
        <ul class="navbar-nav navbar-sidenav" id="menu">
            <li>...</li>
        </ul>
    </div>
</nav>

视口缩小时的示例图像

【问题讨论】：

您的问题是什么？您是否希望它在导航栏顶部弹出而不是展开导航栏？

标签： html css bootstrap-4

【解决方案1】：

只需将 position-absolute 类添加到 dropdown-menu。 不需要额外的 CSS。

<div class="dropdown-menu dropdown-menu-right position-absolute">
   ...
</div>

https://www.codeply.com/go/Q2wqmJnrlB

正如您在此 Bootstrap 4 GitHub issue 上看到的那样，“移动”内的下拉菜单的预期行为（一旦到达 expand-* 断点）导航栏是包含导航栏内的下拉菜单，而不是浮动在它上面。

要改进导航栏布局，您可能还需要将flex-row flex-nowrap 添加到navbar-nav，这样它就不会堆叠并使导航栏太高。

【讨论】：

【解决方案2】：

您需要覆盖引导默认 css。请查看以下示例

@media (max-width: 991px) {
    .custom-navbar .navbar-nav .dropdown-menu {
        position: absolute;
    }
}

<!DOCTYPE html>
<html>
<head>
    <title></title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
    <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/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
</head>
<body>
    <nav class="navbar navbar-expand-lg fixed-top navbar-light bg-light custom-navbar" id="mainNav">
        <a class="navbar-brand" href="/">
            MY Site
        </a>
        <div class="d-flex flex-row order-2 order-lg-3">
            <ul class="navbar-nav flex-row">
                <li style="width:250px;">
                    <select data-placeholder="Jump to site..." id="quickjump-menu" class="form-control form-control-chosen">
                        <option value=""></option>
                        <option value="/sites/site/139/">protein</option>
                        <option value="/sites/site/138/">shake</option>
                        <option value="/sites/site/159/">soup</option>
                        <option value="/sites/site/115/">test 1</option>
                        <option value="/sites/site/116/">test 2</option>
                    </select>
                </li>
                <li class="nav-item dropdown">
                    <a class="nav-link p-2 dropdown-toggle" data-toggle="dropdown" href="#" role="button"
                        aria-haspopup="true" aria-expanded="false">
                        <i class="fa fa-user fa-lg"></i>
                    </a>
                    <div class="dropdown-menu dropdown-menu-right">
                        <div class="dropdown-header text-center">
                            <strong>Admin</strong>
                        </div>
                        <a class="dropdown-item" href="/admin/" target='_blank'>
                            <i class="fa fa-user fa-fw"></i> Admin
                        </a>
                        <a class="dropdown-item" href="/user_info/">
                            <i class="fa fa-users fa-fw"></i> User Info
                        </a>
                        <div class="dropdown-header text-center">
                            <strong>Settings</strong>
                        </div>
                        <a class="dropdown-item" href="/app_settings/">
                            <i class="fa fa-gears fa-fw"></i> App Settings
                        </a>
                        <div class="dropdown-header text-center">
                            <strong>User</strong>
                        </div>
                        <a class="dropdown-item" href="/edit_profile/1/">
                            <i class="fa fa-user fa-fw"></i> User Profile
                        </a>
                        <a class="dropdown-item" href="/logout/?next=/login">
                            <i class="fa fa-gear fa-fw"></i> Log out
                        </a>
                    </div>
                </li>
            </ul>
            <button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse"
                data-target="#navbarResponsive" aria-controls="navbarResponsive" aria-expanded="false"
                aria-label="Toggle navigation">
                <span class="navbar-toggler-icon"></span>
            </button>
        </div>
        <div class="collapse navbar-collapse" id="navbarResponsive">
            <ul class="navbar-nav navbar-sidenav" id="menu">
                <li>...</li>
            </ul>
        </div>
    </nav>
</body>
</html>

【讨论】：

【解决方案3】：

您可以通过覆盖下拉菜单上的响应式position: static 来解决此问题：

css:

.navbar-expand-lg .navbar-nav .dropdown-menu {
  position: absolute;
}

【讨论】：