Your communication object must be able to remove itself from the chain and keep the chain intact. When the communication object does remove itself, it is no longer the active object. This can be carried out as follows:

• Your communication object must process the WM_DESTROY message sent by IPF that corresponds to the closure of a window with which your communication object is associated.

• Your communication object must query the current object window using HM_QUERY. This returns the handle of the current object window.

• Your communication object can then send the HM_UPDATE_OBJCOM_WINDOW_CHAIN message to the handle of the current object window including the handle of your communication object, which was returned when you added your communication object to the chain (see Adding Your Communication Object to the Communication Chain).

The following code fragment illustrates this process:

        case WM_DESTROY:

            hwndPrevious = (HWND) WinQueryWindowULong (hwnd, COM_HWND);

            hwndLatest = (HWND) WinSendMsg (hwnd,
                                     HM_QUERY,
                                     MPFROM2SHORT ((USHORT)0, HMQW_OBJCOM_WINDOW),
                                     NULL);

            WinMessageBox (HWND_DESKTOP,
                           HWND_DESKTOP,
                           (PCH)str,
                           (PCH)"IPF Sample Error Message",
                           1,
                           MB_OK | MB_APPLMODAL |
                           MB_MOVEABLE | MB_ICONASTERISK);
            WinSendMsg (hwndLatest,
                        HM_UPDATE_OBJCOM_WINDOW_CHAIN,
                        (MPARAM) hwndPrevious,
                        (MPARAM) WinQueryWindow (hwnd, QW_PARENT));

            rValue = FALSE;
            break;

        default:

            rValue = TRUE;
            break;

    }
}