Cancel shut down problems.

[Elias Montoya]

Paul, im trying to intercept and cancel the %WM_QUERYENDSESSION, i want to restrict who shuts
down the PC. Unfortunately seems like Firefly doesnt allow me to return a null value, it seems like
it gets overwritten with DefWindowProc() with a %TRUE value...

Any ideas?

[TechSupport]

Hi Elias,

This is a problem message because of the return values that the message returns is opposite to the logic that FireFly employs in the generated code to signify that the code has been processed by the user and therefore bypass the default Windows processing.

Having said that, the message can be dealt with correctly but you need to do a little bit more work. Essentially, you need to subclass the main Form of your application and handle the WM_QUERYENDSESSION in the subclassed procedure. All other messages are sent to FireFly's Form procedure.

Here is the code you need to do the job. Notice that I am using three subclass helper functions (they are part of FireFly 3). 

Code Select Expand




'------------------------------------------------------------------------------------------------------------------------
Function FRMQUERYEND_WM_CREATE ( _
                               hWndForm As Dword, _  ' handle of Form
                               ByVal UserData As Long _  'optional user defined Long value
                               ) As Long

   ' Subclass the main form of the application
   FF_SubClassStart hWndForm, CodePtr(NewFormProc)

End Function



'------------------------------------------------------------------------------------------------------------------------
Function FRMQUERYEND_WM_DESTROY ( _
                                hWndForm      As Dword _  ' handle of Form
                                ) As Long
                               
   ' Reset the original windows procedure
   FF_SubClassEnd hWndForm

End Function



'------------------------------------------------------------------------------------------------------------------------
Function NewFormProc( ByVal hWndForm As Dword, _
                      ByVal wMsg     As Dword, _
                      ByVal wParam   As Dword, _
                      ByVal lParam   As Long _
                      ) As Long

   ' Only handle the one message that we are interested in and
   ' send all other messages to FireFly's code generated window procedure.
   
   Select Case wMsg

      Case %WM_QUERYENDSESSION
         Function = %FALSE      ' prevent application from closing when Windows ends
         Exit Function
         
      Case Else
         Function = FF_SubClassOrig( hWndForm, wMsg, wParam, lParam )
     
   End Select


End Function



'------------------------------------------------------------------------------------------------------------------------
Function FF_SubClassStart( ByVal hWndControl As Dword, _
                           ByVal hNewProc As Dword _
                           ) As Long
   
   Local hOrigProc As Dword
   
   hOrigProc = SetWindowLong( hWndControl, %GWL_WNDPROC, hNewProc )
   SetWindowLong hWndControl, %GWL_USERDATA, hOrigProc
           
End Function


'------------------------------------------------------------------------------------------------------------------------
Function FF_SubClassEnd( ByVal hWndControl As Dword ) As Long

   Local hOrigProc As Dword
   
   hOrigProc = GetWindowLong( hWndControl, %GWL_USERDATA )
   SetWindowLong hWndControl, %GWL_WNDPROC, hOrigProc

End Function


'------------------------------------------------------------------------------------------------------------------------
Function FF_SubClassOrig( ByVal hWndControl As Dword, _
                          ByVal wMsg   As Dword, _
                          ByVal wParam As Long, _
                          ByVal lParam As Long _
                          ) As Long
   
   Local hOrigProc As Dword
   
   hOrigProc = GetWindowLong( hWndControl, %GWL_USERDATA )
   Function = CallWindowProc( hOrigProc, hWndControl, wMsg, wParam, lParam )
           
End Function



[Elias Montoya]

 Thank you very much Paul!

Looking forward testing Firefly 3.

[Roger Garstang]

In one of my apps I think I handled it in PumpHook Special function.  DDT in Forms has the same issue.  This is one of the few API calls that expects a backwards return value and most designers are coded to see 0 as pass to DefProc.