/// <summary>
/// Adds an item to an ItemsControl.
/// </summary>
/// <param name="that">The ItemsControl instance.</param>
/// <param name="item">The item to be inserted.</param>
internal static void AddItem(this ItemsControl that, object item)
{
if (that.ItemsSource == null)
{
that.InsertItem(that.Items.Count, item);
}
else
{
that.ItemsSource.Add(item);
}
}