Relaxed delegates in Visual Basic 8
In C# they have a thing called relaxed delegates that allow you to create an event handler with all parameter types as object and still be able to bind them to an event. Nice
In VB we don't have the same thing, the parameters must match exactly. So the following piece of code doesn’t work
Imports System.Reflection
Imports System.Windows.Forms
Module Module1
Sub Main()
Dim demo AsNew EventDemo
demo.HookEvent()
demo.FireEvent()
EndSub
EndModule
PublicClass EventDemo
Private _textBox AsNew TextBox
PublicSub HookEvent()
AddHandler _textBox.TextChanged, AddressOf MyEventHandler
EndSub
PublicSub FireEvent()
_textBox.Text = "Some text"
EndSub
Sub MyEventHandler(ByVal sender AsObject, ByVal e AsObject)
Console.WriteLine("Event fired, sender = '{0}', e = '{1}'", sender.GetType().FullName, e.GetType().FullName)
EndSub
EndClass
So is there no way to use a generic event handler with all parameters defined as object? Actually there is, its just a bit harder to do. Change the HookEvent to the following and it will work just fine:
PublicSub HookEvent()
Dim eventInfo As EventInfo
Dim methodInfo As MethodInfo
Dim dlg As [Delegate]
eventInfo = _textBox.GetType().GetEvent("TextChanged")
methodInfo = Me.GetType().GetMethod("MyEventHandler")
dlg = [Delegate].CreateDelegate(eventInfo.EventHandlerType, Me, methodInfo)
eventInfo.AddEventHandler(_textBox, dlg)
EndSub
Not exactly the prettiest way of doing it but when you need to it will work
. Lets just hope that relaxed delegates make their way into VB 9 so we can just use the AddHandler syntax, after all it is so much cleaner.
Enjoy!