ItemsControl horizontal content layout

ItemsControl lays out its content vertically by default. To arrange it horizontally we set the Orientation of the StackPanel in the ItemsPanelTemplate. In XAML like this:

<ItemsControl>
   <ItemsControl.ItemsPanel>
      <ItemsPanelTemplate>
         <StackPanel Orientation="Horizontal"/>
      </ItemsPanelTemplate>
   </ItemsControl.ItemsPanel>
</ItemsControl>

And in C#, working from the deepest levels outward, like this:

FrameworkElementFactory factoryPanel =
   new FrameworkElementFactory(typeof(StackPanel));
factoryPanel.SetValue(
   StackPanel.OrientationProperty,
   Orientation.Horizontal);

ItemsPanelTemplate template = new ItemsPanelTemplate();
template.VisualTree = factoryPanel;

ItemsControl itemsControl = new ItemsControl();
itemsControl.ItemsPanel = template;