Non-DDT use of Callbacks ?

[Chris Boss]

I was wondering:

Are Callback functions only usable with DDT code ?

Are the CBxxx functions used with callbacks a product of the DDT engine or simply something associated with a callback ?

Callback coding style would be useful for non-DDT apps, so I was wondering how it can be used.

[Fred Harris]

message crackers?

You talking about message crackers Chris? I always do that to avoid long Select Case blocks. The two ways I do it are either like this...

#Compile Exe
#Include "Win32api.inc"

Type WndEventArgs
  wParam               As Long          'Package parameters to Window Procedure in TYPE
  lParam               As Long
  hWnd                 As Dword
  hInst                As Dword
End Type


Function fnWndProc_OnCreate(Wea As WndEventArgs) As Long
  Local lpCreateStruct As CREATESTRUCT Ptr

  lpCreateStruct=Wea.lParam   'Can use GetModuleHandle() here instead, or, use Global (Hate Globals!)
  [email protected]

  fnWndProc_OnCreate=0
End Function


Function fnWndProc_OnPaint(Wea As WndEventArgs) As Long
  Local pszString As Asciiz Ptr
  Local lpPaint As PAINTSTRUCT
  Local strText As String
  Local hDC As Long

  hDC=BeginPaint(Wea.hWnd,lpPaint)
  Call SetBkMode(hDC,%TRANSPARENT)
  strText = "Hello, World!"
  Call TextOut(hDC,0,0,Byval Strptr(strText),Len(strText))
  Call EndPaint(Wea.hWnd,lpPaint)

  fnWndProc_OnPaint=0
End Function


Function fnWndProc_OnDestroy(Wea As WndEventArgs) As Long
  Call PostQuitMessage(0)
  fnWndProc_OnDestroy=0
End Function


Function fnWndProc(ByVal hWnd As Long,ByVal wMsg As Long,ByVal wParam As Long,ByVal lParam As Long) As Long
  Static Wea As WndEventArgs

  Select Case As Long wMsg
    Case %WM_CREATE
      Wea.hWnd=hWnd : Wea.wParam=wParam : Wea.lParam=lParam
      fnWndProc=fnWndProc_OnCreate(Wea)
      Exit Function
    Case %WM_PAINT
      Wea.hWnd=hWnd : Wea.wParam=wParam : Wea.lParam=lParam
      fnWndProc=fnWndProc_OnPaint(Wea)
      Exit Function
    Case %WM_DESTROY
      Call PostQuitMessage(0)
      fnWndProc=fnWndProc_OnDestroy(Wea)
      Exit Function
  End Select

  fnWndProc=DefWindowProc(hWnd,wMsg,wParam,lParam)
End Function

Function WinMain(ByVal hIns As Long,ByVal hPrev As Long,ByVal lpCL As Asciiz Ptr,ByVal iShow As Long) As Long
  Local winclass As WndClassEx
  Local szAppName As Asciiz*16
  Local Msg As tagMsg
  Local hWnd As Dword

  szAppName="Form1"
  winclass.cbSize=SizeOf(winclass)
  winclass.style=%CS_HREDRAW Or %CS_VREDRAW
  winclass.lpfnWndProc=CodePtr(fnWndProc)
  winclass.cbClsExtra=0
  winclass.cbWndExtra=0
  winclass.hInstance=hIns
  winclass.hIcon=LoadIcon(%NULL, ByVal %IDI_APPLICATION)
  winclass.hCursor=LoadCursor(%NULL, ByVal %IDC_ARROW)
  winclass.hbrBackground=%COLOR_BTNFACE+1
  winclass.lpszMenuName=%NULL
  winclass.lpszClassName=VarPtr(szAppName)
  Call RegisterClassEx(winclass)
  hWnd=CreateWindow(szAppName,"Form1",1040384,200,100,325,300,0,0,hIns,ByVal 0)
  Call ShowWindow(hWnd,iShow)
  While GetMessage(Msg,%NULL,0,0)
    TranslateMessage Msg
    DispatchMessage Msg
  Wend

  Function=msg.wParam
End Function

or like this...

#Compile Exe
#Include "Win32api.inc"

Type WndEventArgs
  wParam As Long
  lParam As Long
  hWnd   As Dword
  hInst  As Dword
End Type

Declare Function FnPtr(wea As WndEventArgs) As Long

Type MessageHandler
  wMessage As Long
  dwFnPtr As Dword
End Type
Global MsgHdlr() As MessageHandler


Function fnWndProc_OnCreate(wea As WndEventArgs) As Long
  Local pCreateStruct As CREATESTRUCT Ptr

  pCreateStruct=wea.lParam
  wea.[email protected]
  fnWndProc_OnCreate=0
End Function


Function fnWndProc_OnNotify(wea As WndEventArgs) As Long
  fnWndProc_OnNotify=0
End Function


Function fnWndProc_OnClose(wea As WndEventArgs) As Long
  Call PostQuitMessage(0)
  fnWndProc_OnClose=0
End Function


Function fnWndProc(ByVal hWnd As Long,ByVal wMsg As Long,ByVal wParam As Long,ByVal lParam As Long) As Long
  Static wea As WndEventArgs
  Register iReturn As Long
  Register i As Long

  For i=0 To 2
    If wMsg=MsgHdlr(i).wMessage Then
       wea.hWnd=hWnd: wea.wParam=wParam: wea.lParam=lParam
       Call Dword MsgHdlr(i).dwFnPtr Using FnPtr(wea) To iReturn
       fnWndProc=iReturn
       Exit Function
    End If
  Next i

  fnWndProc=DefWindowProc(hWnd,wMsg,wParam,lParam)
End Function


Sub AttachMessageHandlers()
  ReDim MsgHdlr(2) As MessageHandler  'Associate Windows Message With Message Handlers
  MsgHdlr(0).wMessage=%WM_CREATE   :   MsgHdlr(0).dwFnPtr=CodePtr(fnWndProc_OnCreate)
  MsgHdlr(1).wMessage=%WM_NOTIFY   :   MsgHdlr(1).dwFnPtr=CodePtr(fnWndProc_OnNotify)
  MsgHdlr(2).wMessage=%WM_CLOSE    :   MsgHdlr(2).dwFnPtr=CodePtr(fnWndProc_OnClose)
End Sub


Function WinMain(ByVal hIns As Long,ByVal hPrev As Long,ByVal lpCL As Asciiz Ptr,ByVal iShow As Long) As Long
  Local hWnd As Dword
  Local winclass As WndClassEx
  Local szAppName As Asciiz * 16
  Local Msg As tagMsg

  szAppName="NewGrid"
  Call AttachMessageHandlers()
  winclass.cbSize=SizeOf(winclass)
  winclass.style=%CS_HREDRAW Or %CS_VREDRAW
  winclass.lpfnWndProc=CodePtr(fnWndProc)
  winclass.cbClsExtra=0
  winclass.cbWndExtra=0
  winclass.hInstance=hIns
  winclass.hIcon=LoadIcon(%NULL, ByVal %IDI_APPLICATION)
  winclass.hCursor=LoadCursor(%NULL, ByVal %IDC_ARROW)
  winclass.hbrBackground=GetStockObject(%LTGRAY_BRUSH)
  winclass.lpszMenuName=%NULL
  winclass.lpszClassName=VarPtr(szAppName)
  RegisterClassEx winclass
  hWnd=CreateWindow(szAppName,"Form1",%WS_OVERLAPPEDWINDOW,200,100,325,300,0,0,hIns,ByVal 0)
  Call ShowWindow(hWnd,iShow)
  While GetMessage(Msg,%NULL,0,0)
    TranslateMessage Msg
    DispatchMessage Msg
  Wend

  Function=msg.wParam
End Function

???

[Chris Boss]

No, I am not refering to message crackers.

I am refering to the Callback function concept itself.

PB Callbacks generate values for the CBxxx functions, rather than pass actual parameters (hWnd&, Msg&, wParam&, lParam&).

Currently callbacks are used with Dialogs (aka. Dialog Procedure) and control callbacks (aka. WM_COMMAND message processing).

My question is:

Can the Callback functionality (and syntax) be used with non-DDT code ?

For example, lets say you write a subclassing routine and instead of passing a normal function as the new window procedure address, could you use a callback function address ?

For example would:

NewWindowAddress = VARPTR(MyCallBackFunction)
SetWindowLong hCtrl&, %GWL_WNDPROC, NewWindowAddress

work and would the callback function properly process the CBxxx functions (or as best it can).

[Michael Mattias]

"CALLBACK FUNCTION DialogProc() AS LONG " is simply (proprietary) shorthand for:

FUNCTION DialogProc (BYVAL CBHNDL AS LONG, BYVAL CBMSG AS LONG,_
        BYVAL CBWPARAM AS LONG, BYVAL CBLPARAM AS LONG) AS LONG

Put that into a PB/CC program where all the "CBxxxx" are not reserved words, and bingo you have a window procedure using all the CBxxxxx words.

Of course to complete the CBxxx functions you'll need a couple of MACROs...

MACRO CBCTL       = LOWRD(CBWPARAM)
MACRO CBCTLMSG = HIWRD(CBWPARAM)

But to answer yiour question directly.....

No, you may not use "CALLBACK FUNCTION" with other window procedures... it may "work" but since it's proprietary AND the doc says the CALLBACK FUNCTION is reserved for procedures used in the CALLBACK option of either CONTROL ADD or DIALOG SHOW, that would be a pure crapshoot.

ALSO, CBHNDL is always a handle to the owner window, so using "CALLBACK FUNCTION" syntax for a subclass procedure would always result in the wrong "hwnd" value when "CBHNDL" is used therein.


MCM