title: Apply animation on WPF control visibility change
body: <p>My xaml is </p>
  
  <pre><code>   &lt;Grid DockPanel.Dock="Top" &gt;
  &lt;DockPanel Background="#bdbec0"  MouseEnter="showTopMenu_MouseEnter" HorizontalAlignment="Stretch" Height="55" &gt;                    
      &lt;Button HorizontalAlignment="Center" VerticalAlignment="Center"&gt;Down&lt;/Button&gt;
  &lt;/DockPanel&gt;
  &lt;DockPanel Background="#151515" LastChildFill="True" Visibility="Collapsed" Name="TopMenuArea"  Height="55"&gt;
   some controls here in a horizontal strip , by default its hidden and when some one click on top button its visible and it wil be hidden when some one click outside this area
  &lt;/DockPanel&gt;
  </code></pre>
  
  <p></p>
  
  <p>And code for button mouse over is</p>
  
  <pre><code>    private void showTopMenu_MouseEnter(object sender, MouseEventArgs e)
      {          
          TopMenuArea.Visibility = Visibility.Visible;
      }
  </code></pre>
  
  <p>How can i apply a animation effect while changing the visibility of TopMenuArea ? Is any way to do it from xaml directly?</p>