.navbar-toggler-icon 没有出现答案

【问题标题】：The .navbar-toggler-icon does not appear.navbar-toggler-icon 没有出现
【发布时间】：2019-06-23 18:15:17
【问题描述】：

<header class="container">
    <div class="container pt-3 col-md-5 col-sm-5 col-xs-6 text-center">
    <a href="#" class="site-logo"><img src="#"></a>
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
    </button>
    </div>

    <nav class="navbar navbar-expand-lg navbar-light bg-light col-xl-6 col-lg-7 col-md-9 container text-center">
        <div class="collapse navbar-collapse" id="navbarSupportedContent">
            <ul class="navbar-nav">
            <li class="nav-item">
                <a class="nav-link" href="#">work</a>
            </li>
            <li class="nav-item">
                <a class="nav-link" href="#">about</a>
            </li>
            <li class="nav-item">
                <a class="nav-link" href="#">contact</a>
            </li>
            <li class="nav-item">
                <a class="nav-link" href="#">artwork</a>
            </li>
            </ul>
        </div>
    </nav>
</header>

当菜单折叠以实现移动响应时，.navbar-toggler-icon 不会出现在 .navbar-toggler 按钮上。

我想要左上方的导航栏按钮

【问题讨论】：

请阅读文档并使用correct Navbar structure。切换器应该在 navbar-expand-lg 元素内。网格类不应用于导航栏。使用网格时，列总是放在row 内。

标签： javascript html css twitter-bootstrap bootstrap-4

【解决方案1】：

仅将此正文代码用于您的引导程序。

<!doctype html>
<html lang="en">
  <head>
    <!-- Required meta tags -->
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">

    <!-- Bootstrap CSS -->
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.2.1/css/bootstrap.min.css" integrity="sha384-GJzZqFGwb1QTTN6wy59ffF1BuGJpLSa9DkKMp0DgiMDm4iYMj70gZWKYbI706tWS" crossorigin="anonymous">

    <title>Hello, world!</title>
  </head>
  <body>
  <!--Main Navigation-->
      <header>
        
        <nav class="navbar navbar-expand-lg navbar-light bg-light col-xl-6 col-lg-7 col-md-9 container text-center">
            <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarTogglerDemo01" aria-controls="navbarTogglerDemo01" aria-expanded="false" aria-label="Toggle navigation">
              <span class="navbar-toggler-icon"></span>
            </button>
            <div class="collapse navbar-collapse" id="navbarTogglerDemo01">
              <a href="#" class="site-logo navbar-brand""><img src="#"></a>
              <ul class="navbar-nav mr-auto mt-2 mt-lg-0">
                  <li class="nav-item">
                      <a class="nav-link" href="#">work</a>
                  </li>
                  <li class="nav-item">
                      <a class="nav-link" href="#">about</a>
                  </li>
                  <li class="nav-item">
                      <a class="nav-link" href="#">contact</a>
                  </li>
                  <li class="nav-item">
                      <a class="nav-link" href="#">artwork</a>
                  </li>
              </ul>
            </div>
          </nav>


      </header>




    <!-- Optional JavaScript -->
    <!-- jQuery first, then Popper.js, then Bootstrap JS -->
    <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/1.14.6/umd/popper.min.js" integrity="sha384-wHAiFfRlMFy6i5SRaxvfOCifBUQy1xHdJ/yoi7FRNXMRBu5WHdZYu1hA6ZOblgut" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.2.1/js/bootstrap.min.js" integrity="sha384-B0UglyR+jN6CkvvICOB2joaf5I4l3gm9GU6Hc1og6Ls7i6U/mkkaduKaBhlAXv9k" crossorigin="anonymous"></script>
  </body>
</html>

【讨论】：