在Visual Studio中，我创建了一个新的ASP.NET核心Web应用程序

然后添加一个下拉菜单（根据引导文档） https://getbootstrap.com/docs/5.1/components/navbar/

html代码的头端如下所示:

<header>
    <nav class="navbar navbar-expand-sm navbar-toggleable-sm navbar-light bg-white border-bottom box-shadow mb-3">
        <div class="container">
            <a class="navbar-brand" asp-area="" asp-page="/Index">WebApplication1</a>
            <button class="navbar-toggler" type="button" data-toggle="collapse" data-target=".navbar-collapse" aria-controls="navbarSupportedContent"
                    aria-expanded="false" aria-label="Toggle navigation">
                <span class="navbar-toggler-icon"></span>
            </button>
            <div class="navbar-collapse collapse d-sm-inline-flex flex-sm-row-reverse">
                <ul class="navbar-nav flex-grow-1">
                    <li class="nav-item">
                        <a class="nav-link text-dark" asp-area="" asp-page="/Index">Home</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link text-dark" asp-area="" asp-page="/Privacy">Privacy</a>
                    </li>
                    <li class="nav-item dropdown">
                      <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-bs-toggle="dropdown" aria-expanded="false">
                        Dropdown
                      </a>
                      <ul class="dropdown-menu" aria-labelledby="navbarDropdown">
                        <li><a class="dropdown-item" href="#">Action</a></li>
                        <li><a class="dropdown-item" href="#">Another action</a></li>
                        <li><hr class="dropdown-divider"></li>
                        <li><a class="dropdown-item" href="#">Something else here</a></li>
                      </ul>
                    </li>
                </ul>
            </div>
        </div>
    </nav>
</header>

但是下拉菜单不起作用。当我单击它时，不会出现下拉列表： https://i.stack.imgur.com/szre4.png

顺晟科技：

确保您的引导程序版本是V5.1，您可以将以下css和js文件添加到项目中:

<header>
    <nav class="navbar navbar-expand-sm navbar-toggleable-sm navbar-light bg-white border-bottom box-shadow mb-3">
        <div class="container">
            <a class="navbar-brand" asp-area="" asp-page="/Index">WebApplication1</a>
            <button class="navbar-toggler" type="button" data-toggle="collapse" data-target=".navbar-collapse" aria-controls="navbarSupportedContent"
                    aria-expanded="false" aria-label="Toggle navigation">
                <span class="navbar-toggler-icon"></span>
            </button>
            <div class="navbar-collapse collapse d-sm-inline-flex flex-sm-row-reverse">
                <ul class="navbar-nav flex-grow-1">
                    <li class="nav-item">
                        <a class="nav-link text-dark" asp-area="" asp-page="/Index">Home</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link text-dark" asp-area="" asp-page="/Privacy">Privacy</a>
                    </li>
                    <li class="nav-item dropdown">
                      <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-bs-toggle="dropdown" aria-expanded="false">
                        Dropdown
                      </a>
                      <ul class="dropdown-menu" aria-labelledby="navbarDropdown">
                        <li><a class="dropdown-item" href="#">Action</a></li>
                        <li><a class="dropdown-item" href="#">Another action</a></li>
                        <li><hr class="dropdown-divider"></li>
                        <li><a class="dropdown-item" href="#">Something else here</a></li>
                      </ul>
                    </li>
                </ul>
            </div>
        </div>
    </nav>
</header>

对于引导程序v4.x，需要将代码更改为:

<header>
    <nav class="navbar navbar-expand-sm navbar-toggleable-sm navbar-light bg-white border-bottom box-shadow mb-3">
        <div class="container">
            <a class="navbar-brand" asp-area="" asp-page="/Index">WebApplication1</a>
            <button class="navbar-toggler" type="button" data-toggle="collapse" data-target=".navbar-collapse" aria-controls="navbarSupportedContent"
                    aria-expanded="false" aria-label="Toggle navigation">
                <span class="navbar-toggler-icon"></span>
            </button>
            <div class="navbar-collapse collapse d-sm-inline-flex flex-sm-row-reverse">
                <ul class="navbar-nav flex-grow-1">
                    <li class="nav-item">
                        <a class="nav-link text-dark" asp-area="" asp-page="/Index">Home</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link text-dark" asp-area="" asp-page="/Privacy">Privacy</a>
                    </li>
                    <li class="nav-item dropdown">
                      <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-bs-toggle="dropdown" aria-expanded="false">
                        Dropdown
                      </a>
                      <ul class="dropdown-menu" aria-labelledby="navbarDropdown">
                        <li><a class="dropdown-item" href="#">Action</a></li>
                        <li><a class="dropdown-item" href="#">Another action</a></li>
                        <li><hr class="dropdown-divider"></li>
                        <li><a class="dropdown-item" href="#">Something else here</a></li>
                      </ul>
                    </li>
                </ul>
            </div>
        </div>
    </nav>
</header>