Prism event aggregator in common user control

Question

In my wpf application I have several user controls, one of them is a TreeView for selection of a particular data type. When selectedItem changes, I publish a selectionChanged event (using Prism's EventAggregator) and a subscriber will get this event. So far, so good.

Now, I start to use the same user control in a new view, actuall in a new window. When selectionChanged event is fired from the new window, both subscriptions are triggered. I would like to specify the sender of the event, so that the subscriber can check who the event is intended for. There are many ways I can do this, but I none that I like so far.

So the question goes out to you guys, how can I achieve this?

Answer 1

The simplest way to achieve this would be to add the sender to your published event args.

public class SelectionChangedEventArgs
{
    public object Sender { get; set; }

    // Other properties (e.g. SelectedItem, etc.)
}

Then as you said, you could easily check the sender to know whether you should handle the event. Prism already provides such a feature, with the following overload of Subscribe:

public virtual SubscriptionToken Subscribe(Action<TPayload> action,
                                           ThreadOption threadOption,
                                           bool keepSubscriberReferenceAlive,
                                           Predicate<TPayload> filter);

So you can actually provide a filter that checks the Sender property when subscribing, so your handler will only be called when this condition is met.