Q:

How to make iteration number/counter in ng-class

How to implement iteration in ng-class ? , below is my code
 <div class="list-message">
      <ul>
        <li ng-repeat="mainList in itemsList" ng-class="{ active: isSet(i++)}" >
          <a href ng-click="setTab(i++) " ng-repeat="x in mainList">
            {{x.message_text}}
          </a>
        </li>
      </ul>
     </div>

   <div class="detail-message">
    <ul ng-repeat="mainList in itemsList track by $index" ng-show="isSet(i++)">
      <li ng-repeat="x in mainList">
        {{x.message_detail}}
      </li>
    </ul>
   </div>

And the result that i want is like the example below.the iterarion inside ng class will be count iterarion number.
  <div class="list-message">
     <ul>
      <li ng-repeat="mainList in itemsList" ng-class="{ active: isSet(1)}" >
         <a href ng-click="setTab(1) " ng-repeat="x in mainList">
            {{x.message_text}}
          </a>
       </li>

      <li ng-repeat="mainList in itemsList" ng-class="{ active: isSet(2)}" >
        <a href ng-click="setTab(2) " ng-repeat="x in mainList">
          {{x.message_text}}
         </a>
       </li>

       <li ng-repeat="mainList in itemsList" ng-class="{ active: isSet(3)}" >
         <a href ng-click="setTab(3) " ng-repeat="x in mainList">
           {{x.message_text}}
         </a>
       </li>
     </ul>
    </div>

   <div class="detail-message">
    <ul ng-repeat="mainList in itemsList track by $index" ng-show="isSet(1)">
      <li ng-repeat="x in mainList">
        {{x.message_detail}}
      </li>
    </ul>
    <ul ng-repeat="mainList in itemsList track by $index" ng-show="isSet(2)">
      <li ng-repeat="x in mainList">
        {{x.message_detail}}
      </li>
    </ul>
    <ul ng-repeat="mainList in itemsList track by $index" ng-show="isSet(3)">
      <li ng-repeat="x in mainList">
        {{x.message_detail}}
      </li>
    </ul>
   </div>

Thank You , appreciate every single your comment and help.

A:

Using $index will help you to keep a track of index. 
$index is a iterator offset of the repeated element (0..length-1).
You can use it like.
 <li ng-repeat="mainList in itemsList" ng-class="{ active: isSet($index)}" >
     <a href ng-click="setTab($index) " ng-repeat="x in mainList">
       {{x.message_text}}
     </a>
   </li>

