In my application I have dialogs with mutiple tabs. Im using Prism to register the views with the TabControl.
What I want is a validation for the entire dialog to diable/enable the save button.
The Problem: Currently we have a view-triggered validation. Means every bound item implements the IDataErrorInfo interface. When the View is displayed the binding triggers the interface and displays and error on the UI. The Control has the HasError Property set to true, save button gets disabled.
But the validation does not get tiggered until the view is displayed. Should I move the validation to the ViewModel and validate the Properties on my own or is there a solution to validate inactive views in a TabControl?
There isn't quite enough information to go off of I your question, so I can only guess. First off, you must understand that there are no inactive views in a TabControl. There is only one view in the TabControls visual tree at one time, and that is the selected tab. This means the other views are removed from the visual tree until they are selected. This really doesn't matter though, as validation is controlled via the ViewModel. You ViewModel most likely has a Command bound to your Save button. This command should have a CanExecute defined returning IDataErrorInfo.Error != null (meaning you have no errors). This is where you will check the validity of your objects. Return false if you have any errors, and true if you don't. Hook into the property changed event of your objects, and call the SaveCommand.RaiseCanExecuteChange method to recheck the state of your button.
If each view a tab has it's own ViewModel, hence it's own Save command, I would recommend using a CompositeCommand. This is really an unknown since I don't know how you have architected your dialogs, views, or ViewModels.