如何在angularJS中将forEach映射到折叠面板

<div ng-app="myApp" ng-controller="myCtrl">
  <div class="panel-group" id="accordion">
    <div class="panel panel-default" ng-repeat="item in items">
      <div class="panel-heading">
        <h4 class="panel-title">
          <a data-toggle="collapse" data-parent="#accordion" href="#collapse{{$index}}">
            {{item.title}}
          </a>
        </h4>
      </div>
      <div id="collapse{{$index}}" class="panel-collapse collapse">
        <div class="panel-body">
          {{item.content}}
        </div>
      </div>
    </div>
  </div>
</div>

var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope) {
  $scope.items = [
    {title: '折叠面板1', content: '折叠面板1的内容'},
    {title: '折叠面板2', content: '折叠面板2的内容'},
    {title: '折叠面板3', content: '折叠面板3的内容'}
  ];
});