Using C Calling Convention Callback Functions in C# and VB - The Easy Way

Imports System
Imports System.Runtime.InteropServices
Imports App.Runtime.InteropServices

Module DelegateGeneratorDemoVB

    Public Delegate Sub CallbackDelegate(ByVal count As Integer)

    Overloads Sub SetCallback(ByVal callback As CallbackDelegate)
        SetCallback(DelegateGenerator.CreateDelegate(callback))
    End Sub

    <DllImport("TestLib.dll", CallingConvention:=CallingConvention.Cdecl)> _
    Overloads Sub SetCallback(ByVal callback As MulticastDelegate)
    End Sub

    <DllImport("TestLib.dll", CallingConvention:=CallingConvention.Cdecl)> _
    Overloads Sub InvokeCallback()
    End Sub

    Sub Main()
        Dim del As CallbackDelegate = AddressOf Callback

        Console.WriteLine("Testing generated delegate...")

        SetCallback(del)

        Try
            For i As Integer = 0 To 9 Step 1
                InvokeCallback()
            Next i
        Catch exc As Exception
            Console.WriteLine(exc)
        End Try

        Console.WriteLine("Testing direct delegate usage...")

        SetCallback(DirectCast(del, MulticastDelegate))

        Try
            For i As Integer = 0 To 9 Step 1
                InvokeCallback()
            Next i
        Catch exc As Exception
            Console.WriteLine(exc)
        End Try
    End Sub

    Sub Callback(ByVal count As Integer)
        Console.WriteLine("Callback invoked for " & count & " time")
    End Sub

End Module