I have inherited some code for a fairly complex WPF application which uses Caliburn.Micro to implementt the MVVM pattern. It uses views bound automatically to view models using the Caliburn naming conventions. The view models inherit from a class that implements INotifyDataErrorInfo, and Fluent Validation is used to generate field-specific errors. This works perfectly, except in one scenario where I have a user control embedded into several different views, and the UI elements within that user control need to be validated.
The embedded user control has it's own view model, which doesn't implement INotifyDataErrorInfo. Suffice to say that the validation messages we generate when validating the parent view do not propagate up to the UI for display.
I'm not quite sure what code I would need to show here to illustrate the problem, so the question is more conceptual really - the question is:
Im my scenario, should I be implementing on the view model behind the embedded user control, or is there some other way to make the parent view call GetErrors() on it's view model with the property names of controls nested within embedded user controls?
I hope that makes sense - I'm quite new to WPF!
I ended up solving this. The problem turned out to be that I had a separate view model bound to the nested view, and that view model did not inherit from a class that implemented INotifyDataErrorInfo. Suffice to say that the rule here seems to be you can have embedded user controls which have their own view model (datacontext) and still get the validation behaviour, but every view model in the hierarchy must implementINotifyDataErrorInfo otherwise the UI elements bound to them won't get notified of errors. In my case it was difficult to see problem because Caliburn.Micro and AutoFac were doing a lot of auto-wiring that was hard to see in a debug context.