In CSLA .NET 3.0 I implemented Csla.Wpf.Validator. This control provides functionality similar to the Windows Forms ErrorProvider control, only in WPF. Of course the ErrorProvider relies on the standard IDataErrorInfo interface, which CSLA supports on behalf of your business objects, and so my Validator control used that same interface.

While I was researching and designing the Validator control, I was in contact with the WPF product team. As a result, I had (shall we say) a "strong suspicion" that my control was a temporary stop-gap until Microsoft provided a more integrated solution. And that's fine - we needed something that worked, and Validator was the ticket.

This blog post provides some good, detailed, insight into the real solution in .NET 3.5: 

Windows Presentation Foundation SDK : Data Validation in 3.5

A couple people have emailed me, asking what I think about this. My answer: I'm happy as can be!

As I say, I knew Validator was temporary. WPF is a version 1.0 technology, and it is very clear that Microsoft will be evolving it rapidly over the next few years. And it is equally clear that WPF must evolve to catch up to, and hopefully exceed, Windows Forms. That means more robust data binding support, including an ErrorProvider equivalent.

So to me, this just means that CSLA .NET 3.5 can drop the Validator control, because there's now a directly supported solution in .NET itself. While this will require changing XAML when moving from .NET 3.0 to 3.5, it is a worthwhile change to make.