private static void OnSetRegionNameCallback(DependencyObject element, DependencyPropertyChangedEventArgs args) { if (element != null) { IRegionManager regionManager = element.GetValue(RegionManagerProperty) as IRegionManager; if (regionManager != null) { string oldRegionName = args.OldValue as string; if (oldRegionName != null) { regionManager.Regions.Remove(oldRegionName); } string newRegionName = args.NewValue as string; if (newRegionName != null) { regionManager.AttachNewRegion(element, newRegionName); } } } }