title: WPF Window fadeIn does not work
body: <p>I have the following code:</p>
  
  <pre><code>&lt;Window.Background&gt;
      &lt;SolidColorBrush Opacity="0.7" Color="White" x:Name="BackgroundBrush"&gt;&lt;/SolidColorBrush&gt;
  &lt;/Window.Background&gt;
  &lt;Window.Triggers&gt;
      &lt;EventTrigger RoutedEvent="Loaded"&gt;
          &lt;EventTrigger.EnterActions&gt;
              &lt;BeginStoryboard&gt;
                  &lt;Storyboard&gt;
                      &lt;DoubleAnimation Storyboard.TargetProperty="Opacity" To="1" Duration="0:0:5" Storyboard.TargetName="BackgroundBrush" From="0.7"&gt;
                      &lt;/DoubleAnimation&gt;
                  &lt;/Storyboard&gt;
              &lt;/BeginStoryboard&gt;
          &lt;/EventTrigger.EnterActions&gt;
      &lt;/EventTrigger&gt;
  &lt;/Window.Triggers&gt;
  </code></pre>
  
  <p>But nothing happened when window is shown. Why?</p>