引导折叠菜单不显示与谷歌地图

我有一个网页，其中有一个引导导航栏和谷歌地图。导航条固定在顶部，谷歌地图被放置，以便填满屏幕的其余部分

<div class="container-fluid">
  <header class="row">
   <nav class="navbar navbar-default" role="navigation">
     <div class="container-fluid">
       <div class="navbar-header">
         <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
           <span class="sr-only">Toggle navigation</span>
           <span class="icon-bar"></span>
           <span class="icon-bar"></span>
           <span class="icon-bar"></span>
         </button>
         <a class="brand" href="#">{{ HTML::image('images/logo.png', array('class'=>'logo')) }}</a>
       </div>
     <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
       <ul class="nav navbar-nav navbar-right">
         <li class="dropdown">
           <a href="#" class="dropdown-toggle" data-toggle="dropdown">Reports <b class="caret"></b></a>
           <ul class="dropdown-menu">
             <li><a href="#">Report 1</a></li>
             <li><a href="#">Report 2</a></li>
             <li><a href="#">Report 3</a></li>
             <li><a href="#">Report 4</a></li>
           </ul>
         </li>
       <li class="dropdown">
         <a href="#" class="dropdown-toggle" data-toggle="dropdown">User <b class="caret"></b></a>
         <ul class="dropdown-menu">
           <li><a href="#">Settings</a></li>
           <li><a href="#">Logout</a></li>
         </ul>
       </li>
     </ul>
   </div>
 </div>
</nav>
</header>
<div id="main">
    <div id="mapcanvas"></div>
</div>
</div>`

加载谷歌地图和导航条没有问题。但是当导航栏折叠，我点击切换按钮时，菜单没有显示。

html,body {width:100%;height:100%;margin:0;padding:0;}
#mapcanvas {
display: block;
position:absolute;
height:auto;
bottom:0;
top:0;
left:0;
right:0;
margin-top:50px;
}