// Simulate a currently non-existing pre-change event
// in DevExpress WinForms 13.2.5
// See http://www.devexpress.com/Support/Center/Question/Details/Q560491

public class MyGalleryControlGallery :
	GalleryControlGallery
{
	// ...

	private GalleryItem MyLastCheckedItem { get; set; }
	internal bool DuringCancelOfCheckChanged { get; set; }

	protected override void OnCheckedChanged(GalleryItem item, bool forceSetItemCheck)
	{
		if (DuringCancelOfCheckChanged) return;

		var lastItem = MyLastCheckedItem;

		var args = new GalleryItemCheckChangingEventArgs
		{
			CurrentItem = lastItem,
			NewItem = item,
			Force = forceSetItemCheck
		};

		// Call my own, new event handler.
		OnItemCheckedChanging(args);

		if (args.Cancel)
		{
			DuringCancelOfCheckChanged = true;
			try
			{
				if (lastItem != null) lastItem.Checked = true;
				item.Checked = false;
			}
			finally
			{
				DuringCancelOfCheckChanged = false;
			}
		}
		else
		{
			base.OnCheckedChanged(item, forceSetItemCheck);
			MyLastCheckedItem = item;
		}
	}

	// ...
}