点击时，Angular Bootstrap手风琴导航栏菜单元素不会展开

Question

用于小屏幕宽度的我的Angular Bootstrap Accordion Navbar菜单元素在单击时不会扩展。任何想法或建议都会非常有用！

代码来源： https://v4-alpha.getbootstrap.com/components/navbar/

我已经在app.component.ts和app.module.ts文件中从ng-bootstrap导入了NgbModal。

import {NgbModal} from '@ng-bootstrap/ng-bootstrap';

以下是app.component.html文件中的cookie cutter bootbarrap navbar：

<nav class="navbar navbar-toggleable-md navbar-light bg-faded">
    <button class="navbar-toggler navbar-toggler-right" 
          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>
  <a class="navbar-brand" href="#">Navbar</a>
  <div class="collapse navbar-collapse"id="navbarSupportedContent">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item active">
        <a class="nav-link" href="#">Home </a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Link</a>
      </li>
    </ul>
    <form class="form-inline my-2 my-lg-0">
      <input class="form-control mr-sm-2" 
             type="text" 
             placeholder="Search">
      <button class="btn btn-outline-success my-2 my-sm-0" 
              type="submit">
      Search</button>
    </form>
  </div>
</nav>