title: WPF C# implementing a resize grip
body: <p>i want to implement a resize grip to my tool. I know that i can activate a grip by setting <code>ResizeMode="CanResizeWithGrip"</code> but i want to grip to be in an Grid, which is only visible on Hovering. 
  I made a Grid with an Image </p>
  
  <pre><code>&lt;Grid x:Name="gridResize" Background="Transparent" &gt;
      &lt;Image x:Name="resizeGrip" HorizontalAlignment="Left" 
             Height="30" 
             VerticalAlignment="Top" 
             Width="27"  
             Source="UserControls/Images/sizegrip.png"/&gt;
  &lt;/Grid&gt;
  </code></pre>
  
  <p>And i have to handle these Events in Code: </p>
  
  <pre><code>private void ResizeGrip_MouseDown(object sender, MouseButtonEventArgs e)
  {
      throw new NotImplementedException();
  }
  
  private void GridResize_MouseLeave(object sender, MouseEventArgs e)
  {
      gridResize.Visibility = Visibility.Hidden;
  }
  
  private void GridResize_MouseEnter(object sender, MouseEventArgs e)
  {
      gridResize.Visibility = Visibility.Visible;
  }
  </code></pre>
  
  <p>Does anyone knows how to implement the Mouse Down Method? </p>