Question

In a WPF application (C#) I’ve got an instance of ObjectX in a class ClassA. This ClassA is instantiated in ClassB.

Hence ClassB -> contains instance of -> ClassA -> which contains an instance of -> ObjectX

ObjectX raises an EventA. I need to handle this event in ClassB.

What is this concept called (Event Delegation, Event Routing, …)? And how can it be done?

Answer 1

In WPF it is called Routed events, but this will work only if both of these are true:

1. We’re speaking about element classes and ‘contains’ means that one of your control actually contain another [and LogicalTreeHelper states that your controls are parents/children to each other.
2. If the event you’re looking for is defined as routed with correct routing strategy – either tunelled or bubbling will work. If it is not then routing events won’t help you.

I have a feeling that all you need is something like this:

in class B:

this.instanceOfA.InstanceOfX.MyEvent += MyHandlerInClassB;

but this has nothing to do with WPF.

---

UPD: or something like this if you don’t want to make instanceOfX accessible:

1. Define the same event on classA and raise it whenever instanceOfX raises its event
2. In ClassB handle instanceOfA.MyEvent

In this case you may keep instanceOfX private but you’ll have to add one more event in the middle.