delegate handling, or incorrect syntax... either way how can i do this?

[Eric Newton]

Given the following code,

Public class ProgressFormMan ager
Public Sub BeginInvoke(ByV al method As [Delegate], ByVal args() As Object)
Dim asyncCallback As New System.Threadin g.WaitCallback( method)
System.Threadin g.ThreadPool.Qu eueUserWorkItem (asyncCallback, args)
End Sub
.... [other implementation details]
End Class

[in the Form codebehind]
Private Sub Button1_Click(. ..
Dim pfm as new ProgressFormMan ager(Me) 'Me is the form to become the
owner
pfm.BeginInvoke (addressof LongMethodCallb ack, new object() { arg1, arg2,
arg3 })
End Sub

Private Sub LongMethodCallb ack(byval param as object)
Dim args() as object = DirectCast(para m, object())
'do lengthy work
End Sub

since ProgressFormMan ager attempts to keep the form created on the same
thread as the caller and then fork a worker thread, I'm using the
QueueUserWorkIt em

problem follows:
A) Vb compiler fails on in ProgressFormMan ager.BeginInvok e with two errors:
1) 'System.Threadi ng.WaitCallback ' is a delegate type. Delegate construction
permits only a single AddressOf expression as an argument list. Often an
AddressOf expression can be used instead of a delegate construction.
2) 'AddressOf' expression cannot be converted to 'System.Delegat e' because
'System.Delegat e' is not a delegate type.

any ideas?

I know in C# this wouldnt even be a problem.

--
Eric Newton
C#/ASP Application Developer
http://ensoft-software.com/
er**@cc.ensoft-software.com [remove the first "CC."]

[David]

On 2004-01-05, Eric Newton <er**@cc.enso ft-software.com> wrote:

Given the following code,

Public class ProgressFormMan ager
Public Sub BeginInvoke(ByV al method As [Delegate], ByVal args() As Object)
Dim asyncCallback As New System.Threadin g.WaitCallback( method)
System.Threadin g.ThreadPool.Qu eueUserWorkItem (asyncCallback, args)
End Sub
... [other implementation details]
End Class
You have to declare method as an actual delegate type. You may as
well use the WaitCallback type, since that's what you want anyway.

Public Sub BeginInvoke(ByV al method as Threading.WaitC allback)
ThreadPool.Queu eUserWorkitem(m ethod, args)
End Sub

And back in the form, it's simply

pfm.BeginInvoke (addressof LongMethodCallb ack)

(I'm not showing the args argument to avoid linebreaks, but obviously
just add that back in).
I know in C# this wouldnt even be a problem.

Actually, you can't pass System.Delegate s around like this in c# either.
In c#, you'd need to explicitly instantiate the delegate when you called
BeginInvoke. VB.Net will do that for you, but you have to let it know
what kind of delegate to create. You can either do that in the function
declaration, as above, or explicitly create the delegate when you call
the function.
--
David
dfoster at
hotpop dot com