title: Change padding of usercontrol based on ComputedVerticalScrollBarVisibility
body: <p>I have a usercontrol that hosts some content inside a scrollviewer, when the window is resized the vertical scroll is set up to show automatically, this all works fine.</p>
  
  <p>I want a trigger on the ComputedVerticalScrollBarVisibility property, that changes the Padding of the actual usercontrol. This is my code right now, why is it not working?</p>
  
  <pre><code>&lt;UserControl x:Class="Something.CustomizableView"
               xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
               xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
               xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
               xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
               xmlns:view="clr-namespace:Something"
               mc:Ignorable="d"
               d:DesignHeight="300" d:DesignWidth="300"&gt;
      &lt;UserControl.Style&gt;
          &lt;Style TargetType="{x:Type Control}"&gt;
              &lt;Setter Property="Padding" Value="20" /&gt;
              &lt;Style.Triggers&gt;
                  &lt;DataTrigger Binding="{Binding ElementName=TheScroll,Path=ComputedVerticalScrollBarVisibility}" Value="Visible"&gt;
                      &lt;Setter Property="Padding" Value="0"&gt;&lt;/Setter&gt;
                  &lt;/DataTrigger&gt;
              &lt;/Style.Triggers&gt;
          &lt;/Style&gt;
      &lt;/UserControl.Style&gt;
  </code></pre>
  
  <p>Here is my ScrollViewer + ItemsControl</p>
  
  <pre><code>&lt;ScrollViewer x:Name="TheScroll" VerticalScrollBarVisibility="Auto" Grid.Row="1"&gt;
              &lt;ItemsControl
                  ItemsSource="{Binding ContentModules}"
                  ItemTemplateSelector="{StaticResource ContentTemplateSelector}"
                  Background="White"&gt;
                  &lt;ItemsControl.ItemContainerStyle&gt;
                      &lt;Style&gt;
                          &lt;Setter Property="FrameworkElement.Margin" Value="0 0 0 50" /&gt;
                      &lt;/Style&gt;
                  &lt;/ItemsControl.ItemContainerStyle&gt;
              &lt;/ItemsControl&gt;
          &lt;/ScrollViewer&gt;
  </code></pre>