Question

I’m trying to write a custom WPF ValidationRule to enforce that a certain property is unique within the context of a given collection. For example: I am editing a collection of custom objects bound to a ListView and I need to ensure that the Name property of each object in the collection is unique. Does anyone know how to do this?

Answer 1

First, I’d create a simple DependencyObject class to hold your collection:

class YourCollectionType : DependencyObject {      [PROPERTY DEPENDENCY OF ObservableCollection<YourType> NAMED: BoundList]  } 

Then, on your ValidationRule-derived class, create a property:

YourCollectionType ListToCheck { get; set; } 

Then, in the XAML, do this:

<Binding.ValidationRules>     <YourValidationRule>        <YourValidationRule.ListToCheck>                <YourCollectionType BoundList='{Binding Path=TheCollectionYouWantToCheck}' />        </YourValidationRule.ListToCheck>     </YourValidationRule> </Binding.ValidationRules> 

Then in your validation, look at ListToCheck’s BoundList property’s collection for the item that you’re validating against. If it’s in there, obviously return a false validation result. If it’s not, return true.