title: Collapsed Items in Wrappanel still need place
body: <p>I have a Wrappanel inside a TreeViewItem. The Items inside the Wrappanel can be made (in)visible by a filter. The problem is that the collapsed Items still need a small place what corrupts the alignment (all Items have a fixed width, Margin and Padding is 0).<br>
  How can I remove the superfluous space?  </p>
  
  <p>Part of the XAML (inside the TreeViewItem Style):  </p>
  
  <pre><code>&lt;Setter Property="ItemsPanel"&gt;
      &lt;Setter.Value&gt;
          &lt;ItemsPanelTemplate&gt;
              &lt;WrapPanel/&gt;
          &lt;/ItemsPanelTemplate&gt;
      &lt;/Setter.Value&gt;
  &lt;/Setter&gt;
  &lt;Setter Property="ItemTemplate"&gt;
      &lt;Setter.Value&gt;
          &lt;DataTemplate&gt;
              &lt;CheckBox IsChecked="{Binding Assigned, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                        ToolTip="{Binding Description}"
                        Click="CheckBox_Clicked"
                        FontFamily="Courier New"
                        Padding="0,0,0,0"
                        Margin="0,0,0,0"&gt;
                  &lt;TextBlock Text="{Binding FixedLengthName}"/&gt;
                  &lt;CheckBox.Visibility&gt;
                      &lt;MultiBinding Converter="{StaticResource PermVisibilityConv}"&gt;
                          &lt;Binding Path="IsChecked" ElementName="ChangesOnly"/&gt;
                          &lt;Binding Path="Changed"/&gt;
                          &lt;Binding Path="Visible"/&gt;
                      &lt;/MultiBinding&gt;
                  &lt;/CheckBox.Visibility&gt;
              &lt;/CheckBox&gt;
          &lt;/DataTemplate&gt;
      &lt;/Setter.Value&gt;
  &lt;/Setter&gt;
  </code></pre>
  
  <p>without filter:<br>
  <a href="https://i.stack.imgur.com/z7oNQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/z7oNQ.png" alt="all items visible"></a>  </p>
  
  <p>with filter:<br>
  <a href="https://i.stack.imgur.com/WTrRc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WTrRc.png" alt="some items collapsed"></a></p>