title: How to add an animation when using Ext.Viewport in Sencha Touch 2
body: <p>Here is my app.js:</p>
  
  <pre><code>Ext.application({
      views: ['SignIn'],
  
      launch: function() {
          // Initialize the signin view
          Ext.Viewport.add(Ext.create('MyApp.view.SignIn'));
      }
  });
  </code></pre>
  
  <p>In <code>MyApp.view.SignIn</code>, I wanna set another view in the <code>Ext.Viewport</code>, so I just wrote <code>Ext.Viewport.setActiveItem(someview)</code>.</p>
  
  <p>It worked well. However, how could I add an animation when doing so?</p>