Watching Tutorial - Basic View App - ActionBar

Source Code:
BasicViewApp.mxml

<?xml version="1.0" encoding="utf-8"?>
<s:ViewNavigatorApplication xmlns:fx="http://ns.adobe.com/mxml/2009"
       xmlns:s="library://ns.adobe.com/flex/spark"
       firstView="views.BasicViewAppUserListView"
       applicationDPI="160">
 <fx:Declarations>
  <!-- Place non-visual elements (e.g., services, value objects) here -->
 </fx:Declarations>
 <s:navigationContent>
  <s:Button label="Back" click="navigator.popView();" />
 </s:navigationContent>
</s:ViewNavigatorApplication>