private void DisposePresentationImages()
{
if (_presentationImages == null)
return;
foreach (PresentationImage image in _presentationImages)
image.Dispose();
_presentationImages.ItemAdded -= OnPresentationImageAdded;
_presentationImages.ItemRemoved -= OnPresentationImageRemoved;
_presentationImages.ItemChanging -= OnPresentationImageChanging;
_presentationImages.ItemChanged -= OnPresentationImageChanged;
_presentationImages = null;
}