AddressOf as parameter

Question

I am building an API where I want a particular method to accept a function pointer. For example I want the consumer of the method to call it like this: MyMethod(AddressOf MyFunction)

I know how to make the method work like this: MyMethod(new MyDelegate(addressof MyFunction)) but I don't want this. I see Microsoft has methods that can pass AddressOf directly. How is this achieved?

Answer 1

Perry,

your method has to take a defined delegate as parameter and then you can simply use the AddressOf Somefunction to call it like:

Public Class Form1
    Private Delegate Sub theDelegate(ByVal somevalue As String)
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        test(AddressOf mytest)
    End Sub
    Private Sub test(ByVal mydel As theDelegate)

    End Sub
    Private Sub mytest(ByVal myvalue As String)

    End Sub
End Class

---

Hannes

If you have got questions about this, just ask.

In a perfect world,
users would never enter data in the wrong form,
files they choose to open would always exist
and code would never have bugs.

C# to VB.NET: http://www.developerfusion.com/tools/convert/csharp-to-vb/

Answer 2

The problem is that I don't know at design time what the delegate signature will be. I want the user to be able to pass in the address of any method without them having to create a delegate and passing that. I am building a scripting engine and I want to abstract the whole delegate stuff from users.

Answer 3

If you dont know the signatures at design time, create your delegate dynamicaly

Here an example

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim Del As [Delegate]
        Del = [Delegate].CreateDelegate(GetType(Action(Of String, Integer)), Me, "MyMethod1")
        ABC.DEF(Del, "AString", 22)
        Del = [Delegate].CreateDelegate(GetType(Action(Of String)), Me, "MyMethod2")
        ABC.DEF(Del, "AString")
    End Sub

    Private Sub MyMethod1(ByVal A As String, ByVal B As Integer)
        Stop
    End Sub

    Private Sub MyMethod2(ByVal A As String)
        Stop
    End Sub
End Class

Class ABC

    Public Shared Sub DEF(ByVal D As [Delegate], ByVal ParamArray Arg() As Object)
        D.DynamicInvoke(Arg)
    End Sub

End Class

Answer 4

Luke,

I did not test it, but for me it looks to a crazy penny lane method. 

In my mind that was the name for these machines which could be used with those big old English Pennies when one Pound was worth the equivalent of the current 5 Euro.

I'm not sure if they use those also in Canada, probably for sure in English Canada.

 

---

Success
Cor

Answer 5

Cool machine !!! I need a few of those.

Can we get the money?

Answer 6

Cor,

The method can also be used for function ... Or dynamicaly create event handlers

Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim Del As [Delegate]
        Del = [Delegate].CreateDelegate(GetType(Action(Of String, Integer)), Me, "MyMethod1")
        ABC.DEF(Del, "AString", 22)
        Del = [Delegate].CreateDelegate(GetType(Func(Of String, Integer)), Me, "MyMethod2")
        Dim TheCount As Integer = CInt(ABC.DEF(Del, "AString"))
        Stop
        Del = [Delegate].CreateDelegate(GetType(EventHandler), Me, "Button1_Click")
        Button1.GetType.GetEvent("Click").AddEventHandler(Button1, Del)
    End Sub
    Private Sub MyMethod1(ByVal A As String, ByVal B As Integer)
        Stop
    End Sub
    Private Function MyMethod2(ByVal A As String) As Integer
        Return A.Length
    End Function
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
        Beep()
    End Sub
End Class
Class ABC
    Public Shared Function DEF(ByVal D As [Delegate], ByVal ParamArray Arg() As Object) As Object
        Return D.DynamicInvoke(Arg)
    End Function
End Class