title: Change the background image of a Button when pressed using VisualStateManager
body: <p>I have this button :</p>
  
  <pre><code>&lt;Button x:Name="PrevAdIcon" Tag="-1" Visibility="Collapsed" Width="80" Height="80" Click="PrevAd"&gt;
      &lt;Button.Background&gt;
          &lt;ImageBrush AlignmentY="Top" Stretch="None" ImageSource="/Images/prev.png"&gt;&lt;/ImageBrush&gt;
      &lt;/Button.Background&gt;
  &lt;/Button&gt;
  </code></pre>
  
  <p>How can I change the background to <code>/Images/prev-selected.png</code> when a user pressed the button ? It'll give him a feedback, since it's a WP7 app</p>
  
  <p>what I have so far (not working) :</p>
  
  <pre><code>&lt;vsm:VisualState x:Name="Pressed"&gt;
                                      &lt;Storyboard&gt;
                                          &lt;ObjectAnimationUsingKeyFrames BeginTime="00:00:00"  Duration="00:00:00.0010000" Storyboard.TargetName="Background" Storyboard.TargetProperty="Background"&gt;
                                              &lt;DiscreteObjectKeyFrame KeyTime="0"&gt;
                                                  &lt;DiscreteObjectKeyFrame.Value&gt;
                                                      &lt;ImageBrush ImageSource="/Images/prev-selected.png" Stretch="Fill"/&gt;
                                                  &lt;/DiscreteObjectKeyFrame.Value&gt;
                                              &lt;/DiscreteObjectKeyFrame&gt;
                                          &lt;/ObjectAnimationUsingKeyFrames&gt;
                                      &lt;/Storyboard&gt;
                                  &lt;/vsm:VisualState&gt;
  </code></pre>