Best practice when not implementing IValueConvert.ConvertBack

Question

Just wondering what people think is the best practice when implementing an IValueConverter which does not have a meaningfull ConvertBack implementation (or one that is only

Answer 1

When ConvertBack contains no functionality, and you are not expecting it to be called, throw a NotImplementedException. It shouldn't have been called and therefore you want a run time exception.

If ConvertBack is intentionally being called, then you had better provide an implementation for it. One option is just to return DependencyProperty.UnsetValue, or handle exceptions within your ConvertBack implementation by returning DependencyProperty.UnsetValue.

My justification for this would be: returning a DependencyProperty.UnsetValue instead of throwing a NotImplementedException makes it unobvious when a ConvertBack method is being invoked when you really never intended it to be. Maybe it should have some functionality now that it is being invoked and throwing a run time exception. It would be much harder to discover the missing ConvertBack functionality if it is just returning DependencyProperty.UnsetValue.