Asynchronous Event Delegation
[vb.net]I was playing around with delegates today and came up with a quick example of how to fire events using delegates in an asynchronous manner (fire an event and continue processing).
Revised Code (Original at bottom):
Public Class Form1
Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
'JUST ADD A STANDARD BUTTON TO YOUR FORM
#End Region
'
'Create instance of class
'
Friend oDelClass As New DelClass
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'
'Add a handler for the event. Could also be done WithEvents .
'
AddHandler oDelClass.DoneProcessing, AddressOf dosomething
End Sub
Public Sub dosomething(ByVal sender As Object, ByVal e As System.EventArgs)
MsgBox("I've been shown from a new thread pool thread!")
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
'
'Call procedure that will raise an event when done.
'
oDelClass.ProcessSomething()
End Sub
End Class
Class Form1
Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
'JUST ADD A STANDARD BUTTON TO YOUR FORM
#End Region
'
'Create instance of class
'
Friend oDelClass As New DelClass
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
'
'Add a handler for the event. Could also be done WithEvents .
'
AddHandler oDelClass.DoneProcessing, AddressOf dosomething
End Sub
Public Sub dosomething(ByVal sender As Object, ByVal e As System.EventArgs)
MsgBox("I've been shown from a new thread pool thread!")
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
'
'Call procedure that will raise an event when done.
'
oDelClass.ProcessSomething()
End Sub
End Class Public Class DelClass
'
'Delegate (function pointer)
'
Friend Delegate Sub MyEventHandler(ByVal sender As Object, ByVal e As System.EventArgs)
'
'Instance of the function pointer that points to OnDoneProcessing.
'
Private MyEventInvoker As New MyEventHandler(AddressOf OnDoneProcessing)
'
'Event declaration where MyEventHandler is simply an interface.
'Could be: Friend MyEvent(byval sender as object, byval e as system.eventargs)
'
Friend Event DoneProcessing As MyEventHandler
'
'Overidable event calling procedure.. standard .NET event design
'
Friend Overridable Sub OnDoneProcessing(ByVal sender As Object, ByVal e As System.EventArgs)
'
'If OnDoneProcessing was called using BeginInvoke, then you are already running in a thread
'pool thread parallel to the caller thread (async).
'
'Fire the event
'
RaiseEvent DoneProcessing(sender, e)
End Sub
Friend Sub ProcessSomething()
'
'Perform some processing that in return raises an event...
'
'Calls OnDoneProcessing, which raises the event, in a new thread.
'
Call MyEventInvoker.BeginInvoke(New Object, New System.EventArgs, Nothing, Nothing)
'
'You could also use a function, then use EndInvoke, or a callback, to get the return.
'That is beyond the needs of this example, but here is a link:
'http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconasynchronousdelegatesprogrammingsample.asp?frame=true
'
End Sub
End Class
Class DelClass
'
'Delegate (function pointer)
'
Friend Delegate Sub MyEventHandler(ByVal sender As Object, ByVal e As System.EventArgs)
'
'Instance of the function pointer that points to OnDoneProcessing.
'
Private MyEventInvoker As New MyEventHandler(AddressOf OnDoneProcessing)
'
'Event declaration where MyEventHandler is simply an interface.
'Could be: Friend MyEvent(byval sender as object, byval e as system.eventargs)
'
Friend Event DoneProcessing As MyEventHandler
'
'Overidable event calling procedure.. standard .NET event design
'
Friend Overridable Sub OnDoneProcessing(ByVal sender As Object, ByVal e As System.EventArgs)
'
'If OnDoneProcessing was called using BeginInvoke, then you are already running in a thread
'pool thread parallel to the caller thread (async).
'
'Fire the event
'
RaiseEvent DoneProcessing(sender, e)
End Sub
Friend Sub ProcessSomething()
'
'Perform some processing that in return raises an event...
'
'Calls OnDoneProcessing, which raises the event, in a new thread.
'
Call MyEventInvoker.BeginInvoke(New Object, New System.EventArgs, Nothing, Nothing)
'
'You could also use a function, then use EndInvoke, or a callback, to get the return.
'That is beyond the needs of this example, but here is a link:
'http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconasynchronousdelegatesprogrammingsample.asp?frame=true
'
End Sub
End Class James made an excellent blog that inherits from a button and mirrors the standard click event with an ASync version. This design is very flexible, and suitable for use with any inheritable class that has events.