Even if your communication object is the only one in use, your communication object is still part of the communication chain. To add itself to the chain, your communication object must:

• Send the help manager message HM_SET_OBJCOM_WINDOW to the window PACVP->hWnd Parent.

  Your communication object must pass its frame handle as the first parameter.

• Your communication object must receive and store the window handle it receives in return.

• Your communication object should pass all HM_ help manager messages to that window handle.

The following code fragment illustrates this process.

#define INCL_WIN#define INCL_WINHELP
#include <os2.h>

#define HM_MSG_MAX (HM_MSG_BASE+0x0024)

USHORT   IPFClassRegistered = 0;         /* IPF class registered flag        */

/* Main Entry point */
MRESULT EXPENTRY IPFMain (PACVP pACVP, PCH Parameter);

/* Pop up error box */
VOID Error (PCH str);


MRESULT EXPENTRY IPFMain (PACVP pACVP, PCH Parameter)
/* pACVP contains the following structure:

   typedef struct_ACVP
   {
      ULONG  cb;                   length
      HAB    hAB;                  anchor block handle
      HMQ    hmq;                  messge queue handle
      ULONG  ObjectID;             object identifier
      HWND   hWndParent;           IPF viewport client handle
      HWND   hWndOwner;            IPF viewport client handle
      HWND   hWndACVP;             applications frame window hwnd
   } ACVP, *PACVP;

This structure is prefilled in except for hWndACVP.  You must put your
window handle there if you are creating an application-controlled viewport.
If this is just a generic communication object, you do not need to fill it in.

Parameter is the information passed in with the objectinfo tag.

Note: You can use ObjectID to have multiple acviewports and comm objects
use the same entry point.  Check the ObjectID to find out where you were
called from in the IPF file. */

{
    HWND  hwndFrame, hwndPrevious, hwndLatest, hwndClient;
    ULONG CtrlData = 0;

    Error ( Parameter );
    /* Check global to see if our window class has been registered. */
    /* if not, register it.                                         */
    if (!IPFClassRegistered)
    {
        /* We will register our class with 4 extra bytes of information
           so that we can place the previous object comm window handle there.
           You might want to create a structure store here instead. */
        if (!WinRegisterClass( pACVP->hAB,
                               "CLASS_IPF",
                               (PFNWP) IPF_WinProc,
                               CS_SYNCPAINT | CS_SIZEREDRAW | CS_MOVENOTIFY,
                               4))
        {
            Error ("Can not register class");
            exit (TRUE);
        }
        IPFClassRegistered = 1;
    }

    /* Create window.  Visibility does not matter, as IPF will take care
       of it. */
    if (!(hwndFrame = WinCreateStdWindow (pACVP->hWndParent,
                                          WS_VISIBLE,
                                          &CtrlData,
                                          "CLASS_IPF",
                                          "IPF",
                                          0L,
                                          0L,
                                          0L,
                                          &hwndClient
                                          )))
    {
        Error ("Can not create window");
        return (MRESULT) TRUE;
    }

    /* Setup our window in the ACVP structure.  This is only necessary if
       you are creating an acviewport. */
    pACVP->hWndACVP = hwndFrame;

    /* Set the current comm object window to us */
    hwndPrevious = (HWND) WinSendMsg (pACVP->hWndParent,
                                      HM_SET_OBJCOM_WINDOW,
                                      (MPARAM) hwndFrame,
                                      (MPARAM)NULL);

    /* Query back the comm obj window */
    hwndLatest = (HWND) WinSendMsg (pACVP->hWndParent,
                                    HM_QUERY,
                                    MPFROM2SHORT ((USHORT)0, HMQW_OBJCOM_WINDOW),
                                    (MPARAM)NULL);

    /* double check to make sure we are in the comm chain */
    if (hwndFrame != hwndLatest)
    {
        Error ("Can not set object communication window");
        return (MRESULT) TRUE;
    }

    /* Store the previous commobj handle in window words */
    if (!WinSetWindowULong (hwndClient, QWL_USER, (ULONG) hwndPrevious))
    {
        Error ("Can not save handle into reserved memory");
        return (MRESULT) TRUE;
    }
    return (MRESULT) FALSE;
}

VOID Error (PCH str)

{
    WinMessageBox (HWND_DESKTOP,
                   HWND_DESKTOP,
                   (PCH)str,
                   (PCH)"IPF Sample Error Message",
                   1,
                   MB_OK | MB_APPLMODAL |
                   MB_MOVEABLE | MB_ICONASTERISK);
}