用ng-class和ng-click切换手风琴面板图标

我有一个带有“ V形”图标的手风琴，单击该图标可将其指向上方或下方，这是通过ng-click和完成的ng-class。手风琴只允许同时打开一个面板-因此，当我单击关闭的面板时，打开的面板将关闭。但是，如何在即将关闭的打开面板上切换人字形图标ng-click呢？

本来我可以用DOM操作等来做到这一点，但是由于这是角度视图的局部视图，因此我无法做到。

码：

<div class="panel-group" id="accordion">
  <div class="panel panel-default">
    <div class="panel-heading">
      <h4 class="panel-title">
        <a data-toggle="collapse" data-parent="#accordion" href="#collapseOne" ng-click="firstpaneisopen=!firstpaneisopen">
           <i class="glyphicon" ng-class="{'glyphicon-chevron-up': firstpaneisopen, 'glyphicon-chevron-down': !firstpaneisopen}"></i> Collapsible Group Item #1
         </a>
      </h4>
     </div>
    <div id="collapseOne" class="panel-collapse collapse in">
     <div class="panel-body">
       Body
     </div>
    </div>
  </div>
  <div class="panel panel-default">
   <div class="panel-heading">
     <h4 class="panel-title">
       <a data-toggle="collapse" data-parent="#accordion" href="#collapseTwo" ng-click="secondpaneisopen=!secondpaneisopen>
         <i class="glyphicon" ng-class="{'glyphicon-chevron-up': secondpaneisopen, 'glyphicon-chevron-down': !secondpaneisopen}"></i> Collapsible Group Item #2
       </a>
     </h4>
    </div>
    <div id="collapseTwo" class="panel-collapse collapse">
     <div class="panel-body">
       Body
     </div>
    </div>
   </div>
 </div>