Question

I am trying to test out very simple event handling in VB.NET.

So far I have:

Public Delegate Sub TestEventDelegate()
Public Event TestEvent As TestEventDelegate

Sub MySub
    Raise TestEvent
End Sub

How would you write an event handler for the above event that just displayed a simple MessageBox?

Answer 1

Writing the handler method is simple – just write a Sub which takes no parameters and displays a message box.

You then need to subscribe the handler to the event, which you can either do adding a Handles clause to the method:

Sub ShowMessageBox() Handles foo.TestEvent

Or by using an AddHandler statement:

AddHandler foo.TestEvent, AddressOf ShowMessageBox

Note that to follow .NET conventions, your delegate should have two parameters – one of type Object to specify which object raised the event, and one of type EventArgs or a subclass, to provide any extra information. This isn’t required by the language, but it’s a broadly-followed convention.