Question

How can I raise an event from another class which implements an interface that contains an event?

Public Interface IMyEvent
    Event MyEvent()
End Interface

Public Class ClassA
    Implements IMyEvent

    Public Event MyEvent() Implements IMyEvent.MyEvent

End Class

Public Class ClassB
    Public myClassA As New ClassA

    Public Sub New()
        Dim myIEvent As IMyEvent = CType(myClassA, IMyEvent)
        RaiseEvent myIEvent.MyEvent ' Doesn't work.
    End Sub
End Class

Note the comment – that code doesn’t work. How can I raise an event like this, if it’s contained within another class through an interface?

Answer 1

First, the reason you can’t do this is because events can only be called on the class in which they are declared.

The usual way around this is to provide a protected OnEventName() method, which invokes the event. Then, you can inherit from the class and either call or override the OnEventName() method to invoke the event. If you really want to be able to do this from a class that is unrelated in the hierarchy, you can add the OnEventName() method to the interface you declared.