events and delegates ??

[Chris]

Hi,

what is the difference between using events and delegates (apart from the
syntax) ?

have a look at following (working) programs please
(you can just copy/paste and build it) :

First program uses delegates, the second events but both do inherently the
same :

Using delegates :
Imports System
Public Delegate Sub WakeUpDelegate( )

class AClass
Public Shared Sub WakeUpA()
Console.WriteLi ne("WakeUpA()" )
End Sub
End Class

Class Timer
Public deleg As WakeUpDelegate
Public Sub Alarm()
If Not deleg Is Nothing Then
deleg()
End If
End Sub
End Class

Class Program
Public Shared Sub Main()
Console.WriteLi ne("Using Delegates (VB)")
Dim objTimer As Timer = New Timer
Dim callback As WakeUpDelegate = New WakeUpDelegate( AddressOf
AClass.WakeUpA)
objTimer.deleg = CType([Delegate].Combine(objTim er.deleg, callback),
WakeUpDelegate)
objTimer.Alarm( )
End Sub
End Class


Using events :
Imports System
Public Delegate Sub WakeUpDelegate( )

class AClass
Public Shared Sub WakeUpA()
Console.WriteLi ne("WakeUpA()" )
End Sub
End Class

Class Timer
Public Event deleg As WakeUpDelegate
Public Sub Alarm()
RaiseEvent deleg()
End Sub
End Class

Class Program
Public Shared Sub Main()
Console.WriteLi ne("Using Events (VB)")
Dim objTimer As Timer = New Timer
AddHandler objTimer.deleg, AddressOf AClass.WakeUpA
objTimer.Alarm( )
End Sub
End Class



Thanks for any help
Chris

[Jay B. Harlow [MVP - Outlook]]

Re: events and delegates ??

Chris,
The way I view it is:

Events are implemented in terms of a Delegate, similar to how a Property is
implemented in terms of a Field.

The Event protects the underlying Delegate, similar to how a Property
protects the underlying Field.

In other words you use Events when you want to encapsulate the Delegate,
similar to how you use a Property when you want to encapsulate a field.

See:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcn7/html/vaconEventsDelegatesInheritance.asp

Hope this helps
Jay

"Chris" <christianc@pan dora.be> wrote in message
news:Pd3zb.5648 7$BG5.1981470@p hobos.telenet-ops.be...[color=blue]
> Hi,
>
> what is the difference between using events and delegates (apart from the
> syntax) ?
>
> have a look at following (working) programs please
> (you can just copy/paste and build it) :
>
> First program uses delegates, the second events but both do inherently the
> same :
>
> Using delegates :
> Imports System
> Public Delegate Sub WakeUpDelegate( )
>
> class AClass
> Public Shared Sub WakeUpA()
> Console.WriteLi ne("WakeUpA()" )
> End Sub
> End Class
>
> Class Timer
> Public deleg As WakeUpDelegate
> Public Sub Alarm()
> If Not deleg Is Nothing Then
> deleg()
> End If
> End Sub
> End Class
>
> Class Program
> Public Shared Sub Main()
> Console.WriteLi ne("Using Delegates (VB)")
> Dim objTimer As Timer = New Timer
> Dim callback As WakeUpDelegate = New WakeUpDelegate( AddressOf
> AClass.WakeUpA)
> objTimer.deleg = CType([Delegate].Combine(objTim er.deleg,[/color]
callback),[color=blue]
> WakeUpDelegate)
> objTimer.Alarm( )
> End Sub
> End Class
>
>
> Using events :
> Imports System
> Public Delegate Sub WakeUpDelegate( )
>
> class AClass
> Public Shared Sub WakeUpA()
> Console.WriteLi ne("WakeUpA()" )
> End Sub
> End Class
>
> Class Timer
> Public Event deleg As WakeUpDelegate
> Public Sub Alarm()
> RaiseEvent deleg()
> End Sub
> End Class
>
> Class Program
> Public Shared Sub Main()
> Console.WriteLi ne("Using Events (VB)")
> Dim objTimer As Timer = New Timer
> AddHandler objTimer.deleg, AddressOf AClass.WakeUpA
> objTimer.Alarm( )
> End Sub
> End Class
>
>
>
> Thanks for any help
> Chris
>
>[/color]

[Armin Zingler]

Re: events and delegates ??

"Chris" <christianc@pan dora.be> schrieb[color=blue]
>
> what is the difference between using events and delegates (apart from
> the syntax) ?
>
> have a look at following (working) programs please
> (you can just copy/paste and build it) :
>
> First program uses delegates, the second events but both do
> inherently the same :
> [sample code][/color]


The difference is that an event is a MulticastDelega te, i.e. raising the
event can notify an unlimited number of objects about the event. Simplified,
an event is an array of delegates (AFAIR, in fact it is a linked list).


--
Armin

http://www.plig.net/nnq/nquote.html

http://www.netmeister.org/news/learn2quote.html

[Jay B. Harlow [MVP - Outlook]]

Re: events and delegates ??

Armin,[color=blue]
> The difference is that an event is a MulticastDelega te,[/color]
A delegate can be multicast also, remember MulticastDelega te inherits from
Delegate. Although I agree with your statement in that most of the time a
Delegate variable are single callbacks.

Try the following to see what I mean.

Private Delegate Sub Stuff()

Public Sub Main
Dim a, b, c As Stuff
a = AddressOf Method1
b = AddressOf Method2
c = DirectCast([Delegate].Combine(a, b), Stuff)
c.Invoke()
End Sub

Public Sub Method1()
Debug.WriteLine ("Hello", "Method1")
End Sub

Public Sub Method2()
Debug.WriteLine ("Goodbye", "Method2")
End Sub

Hope this helps
Jay



"Armin Zingler" <az.nospam@free net.de> wrote in message
news:OXhmKbPuDH A.2308@TK2MSFTN GP11.phx.gbl...[color=blue]
> "Chris" <christianc@pan dora.be> schrieb[color=green]
> >
> > what is the difference between using events and delegates (apart from
> > the syntax) ?
> >
> > have a look at following (working) programs please
> > (you can just copy/paste and build it) :
> >
> > First program uses delegates, the second events but both do
> > inherently the same :
> > [sample code][/color]
>
>
> The difference is that an event is a MulticastDelega te, i.e. raising the
> event can notify an unlimited number of objects about the event.[/color]
Simplified,[color=blue]
> an event is an array of delegates (AFAIR, in fact it is a linked list).
>
>
> --
> Armin
>
> http://www.plig.net/nnq/nquote.html
> http://www.netmeister.org/news/learn2quote.html
>
>[/color]