Question

Is there an equivalent to AddressOf in Visual Basic 4?

I am attempting to get some Visual Basic 5/6 code that adds menu items to my form’s system menu working in VB4. Below is the code snippet that will not compile:

'Add Custom Menu To System Menu
Call AppendMenu(GetSystemMenu(Me.hWnd, 0&), MF_SEPARATOR, 0&, vbNullString)
Call AppendMenu(GetSystemMenu(Me.hWnd, 0&), MF_STRING, IDM_SYSTEMTRAY, "Minimize To &System Tray")
Call AppendMenu(GetSystemMenu(Me.hWnd, 0&), MF_STRING, IDM_ABOUT, "&About...")
procOld = SetWindowLong(hWnd, GWL_WNDPROC, AddressOf WindowProc)

Here is the API declarations from the module:

' Win32 API
Public Const MF_SEPARATOR = &H800&
Public Const MF_STRING = &H0&
Public Const GWL_WNDPROC = (-4)
Public Declare Function GetSystemMenu Lib "user32" (ByVal hWnd As Long, ByVal bRevert As Long) As Long
Public Declare Function AppendMenu Lib "user32" Alias "AppendMenuA" (ByVal hMenu As Long, ByVal wFlags As Long, ByVal wIDNewItem As Long, ByVal lpNewItem As Any) As Long
Public Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Public Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hWnd As Long, ByVal msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Public Const WM_SYSCOMMAND = &H112

' User Created
Public procOld As Long
Public Const IDM_ABOUT As Long = 1010
Public Const IDM_SYSTEMTRAY As Long = 1011

And finally, the code for WindowProc:

Public Function WindowProc(ByVal hWnd As Long, ByVal iMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
    Select Case iMsg
        Case WM_SYSCOMMAND
            Select Case wParam
                Case IDM_ABOUT
                   MsgBox "About goes here..."
                   Exit Function
               Case IDM_SYSTEMTRAY
                   MsgBox "Send to system tray code goes here..."
                   Exit Function
            End Select
    End Select
    ' Pass all messages on to VB and then return the value to windows
    WindowProc = CallWindowProc(procOld, hWnd, iMsg, wParam, lParam)
End Function

Any other pointers or alternate methods of adding items to my form’s system menu would be appreciated too!

Answer 1

From: Xtreme VB Talk: AddressOf work around for vb4

[Banjo]
I don’t think that you can without resorting to somesort of outside
DLL written in C.

[OnErr0r]
Matt Curland wrote just such a dll. Allows you to get the address of a class function, even works with vb5/6.

You can download callback.zip from the above page after registering. As a fallback, you can get the file here: callback.zip

EDIT: The direct download link has been removed, because it appears that this source code is part of a book by Matt Curland and copyrighted.