CODEWITHSUNDEEP
.netcomvb6interop
HardcoreGamer
HardcoreGamer

Reputation: 1193

Pass VB Function callback as parameter to .NET

Part of a Visual Basic program is being moved to .NET dll.

Parameter call can be passed successfully & everything run fine.

How can I pass a callback function of VB6 for .NET to call after a long running async task?

In .NET

Public Delegate Function VBCallBackFunc() As Integer

Public Function DoSomething(a As String, b As String, c As String, _
parent As IntPtr, Optional ByVal CallbackAddr As VBCallBackFunc = Nothing) As Boolean Implements _DotNetLib.DoSomething

VB6

result = DotNetLib.DoSomething(strA, strB, strC, Me.hwnd, AddressOf DotNetCallback)

Public Function DotNetCallback() As Long
    MsgBox ("Callback")
End Function

In object browser of VB:

Function DoSomething(strA As String, strB As String, strC As String,
 parent As Long, [CallbackAddr As VBCallBackFunc]) As Boolean

Member of DotNetLib

But it said "Invalid use of AddressOf operator" ???

Upvotes: 1

Views: 1428

Answers (1)

tcarvin
tcarvin

Reputation: 10855

The comments related to using Events are a good option, but I tend to use interfaces more, so here is a solution for that.

(Free-hand code, you will need to syntax check and the names can be cleaned up, they are just for illustration purposes)

In .NET:

Create an COM exposed interface for your callback:

Public Interface IVBCallBack
   Public Function VBCallBackFunc() As Integer
End Interface

Change your DoSomething be like this:

Public Function DoSomething(a As String, b As String, c As String, parent As IntPtr, ByVal CallbackAddr As IVBCallBack) As Boolean

In VB6:

result = DotNetLib.DoSomething(strA, strB, strC, Me.hwnd, Me)

(And you will need your class, control, or form to Implements IVBCallBack)

Public Function IVBCallBack_VBCallBackFunc() As Long
    MsgBox ("Callback")
End Function

Be sure to have a method on the .NET side to clean up and release all your references since .NET is holding a reference to the VB6 object.

One other thing to note. DO NOT CALL BACK INTO VB6 ON ANY THREAD OTHER THAN THE MAIN UI THREAD!

Upvotes: 3

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