Inheriting from one base class that implements INotifyPropertyChanged?

This is a very common base class to have in WPF or Silverlight development and won't noticeably affect performance. The only problem I have with PropertyNotifier as a base class results from being restricted to single inheritance but that tends to be a rare issue with the type of class you'll need it for.

Yes, thats very common practice. For a large scale application it becomes necessary to have this kind of base class. We had also created a BaseViewModel for the same purpose; we also implemented a lot of common code(across ViewModels) in this base class like logging, displaying error messages, initializing WCF proxy objects etc.

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