WPF - Why isn't ValidationRule a DependencyObject?

Question

Is there a technical reason why ValidationRule is not a DependencyObject?

Answer 1

Unfortunately in WPF who you derive from is often the difference between something that just works and something that is totally useless. But in general, the class designers want to pick the least possible base class that they needed. There's really no reason that ValidationRule needs to be tied to WPF at all other than the fact that it's defined in a WPF assembly. But as we're finding out, that makes it quite painful to do what you're trying to do.