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Asked: 2026-06-17T23:58:55+00:00

I have been trying to get a function to work asynchronously with a GUI

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I have been trying to get a function to work asynchronously with a GUI window, and having very limited success.

The code below is my function, XXX, with a delegate and Callback – to allow stopping the GUI thread, without getting an error.

It works though – if it is a Sub, not a function, and if it doesn’t have any arguments.

I don’t know how to change it so I can check its return value… I have found a little help in some examples, http://msdn.microsoft.com/en-us/library/system.iasyncresult.asyncstate.aspx – but they print the return value in the callback, and I can’t see how to get it in the caller.

I can’t find any way to use arguments in my function.

Private Function XXX_Callback(ByVal ia As IAsyncResult) 
    Dim d As XXXDelegate = CType(CType(ia, Runtime.Remoting.Messaging.AsyncResult).AsyncDelegate, XXXDelegate)
    d.EndInvoke(ia)

    Dim result As AsyncResult = CType(ia, AsyncResult)
    Dim caller As XXXDelegate = CType(result.AsyncDelegate, XXXDelegate)
    Dim returnValue As Boolean = caller.EndInvoke(ia)

    XXX_Finish()   ' needs the "vvv argument, I don't know how to get it
    ' The returnValue is here but I don't know how to send it to the caller
End Function

'Private Function XXX_Finish(ByVal vvv as Boolean) As Boolean
' this probably needs to return something, I don't know what/ how to get it
Private Function XXX_Finish() As Boolean
    ' something 
    myGui.Finish()            
End Function

' Private Delegate Function XXXDelegate(ByVal vvv As Integer) As Boolean
' Public Function XXX(ByVal vvv As Integer) As Boolean    ' This is what I would like
Private Delegate Sub XXXDelegate()
Public Sub XXX() 
    '
    myGui.Update()
    '
End Sub

Public Sub Caller()
    '
    myGui = New SomeGui()
    myGui.Begin()
    Dim t As New XXXDelegate(AddressOf XXX)
    t.BeginInvoke(AddressOf XXX_Callback, Nothing)
    ' more code, another call
End Sub

Private myGui As SomeGui

Please, could someone help me get this into a better shape, or get some examples that will help ? With the ones I have found in the past two days, I have reached a dead end…

Thank you.

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1 Answer

  1. Editorial Team

    After searching through lots of posts on the web, and reading a couple of books, I have found the best resource, with examples for each case that one might encounter:

    http://support.microsoft.com/kb/315582

    The answers to this particular question are in the above link, “Sample 2: Calling A Method Asynchronously by Using the EndInvoke() Call Pattern” and “Sample 5: Executing a Callback When an Asynchronous Method Completes.”

    The best thing about it though is the simple and organized fashion in which the options to use Invoke, EndInvoke, Callback are explained.

    One thing to note: for my question above, the essential breakthrough was when I read the words “BeginInvoke() returns immediately and does not wait for the asynchronous call to complete.“

    So… trying to call another method, after it, was the wrong approach.

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