06170308.txt 20-Jun-00


SystemParametersInfo() function

Hi all

Has anyone had any experience of using
  SystemParametersInfo() function.
I am trying to stop my end user from using the W95 key and
  the Ctrl + Esc keys to bring up the Start Menu whilst my
  programme is running.
I have been told that I can use the API function
  SystemParametesInfo() along with the Parameter
  SPI_SCREENSAVERRUNNING. This function is supposed to trick
  the system into thinking that your programme is a screen
  saver.
I received this information from two different sources, one
  from VB and one from Delphi.
They both use the same function with the same parameter. Yet
  when I try to use this with VO I am unable to get it to
  work. I hope that they do not have one over on us.
I'm sure there must be a way to stop the Start Menu from
  being accessed whilst the programme is running.
Any help is appreciated. But then I'm sure that goes without
  saying.

Cheers
Adrian


Hello Adrian,

This should do what you want.
// 2nd param with a value of 1 disables Alt+Tab.
// Send send 0 to enable.
// 1 disables
SystemParametersInfo (SPI_SCREENSAVERRUNNING, 1, NULL, 0)
// 0 enables
SystemParametersInfo (SPI_SCREENSAVERRUNNING, 0, NULL, 0)

Hope it helps.
Butch Nash


Hi Voyagers

Just curiosity:
Why would someone want to block the User from acessing the
  start menu?

Adriano Rui Gominho


I would.  I have an app that will be used as data entry for
  shop floor workers.
All they see is a screen that lets them choose one thing and
  another and start/end a job.
It uses the keyboard, no mouse and I wouldn't want these
  guys to fiddle around the system.
That's why I hide the Taskbar :)

========Stephane Hebert========


I use the following to hide the Taskbar and then show it
  again when the app is exited.
It doesn't seem to work in Win98 though, I just tried it.  I
  know it works with Win95.
I don't know if pressing CTRL+ESCAPE will show it back up on
  the screen once it's hidden, I'll have to try when I get
  back to my dev machine.
Method Start() class App
  local hwnd as ptr
  hwnd:=FindWindow(String2Psz("Shell_TrayHwnd"),null)
  if !IsNil(hwnd)
    ShowWindow(hwnd,SW_HIDE)
  endif
  self:Exec()
  ShowWindow(hwnd,SW_RESTORE)

========Stephane Hebert========


Stephane

In Win98 the classname for the taskbar is "Shell_TrayWnd"
See if that makes any difference.

regards
Trevor


Trevor,

Yep, that did it.  Now why did they change that ?  Makes no
  sense to me.
To come back to Adrians problem, pressing CTRL+ESCAPE when
  the Taskbar is hidden doesn't prevent the start menu from
  poping up.
Surely there's another way.

========Stephane Hebert========


Stephane

>Surely there's another way.
You would probably have to put in a system wide hook to
  capture/filter all keystrokes before the system got them
  and suppress the ones you don't want to get through.
This has to be in a DLL - see extract below from the Win32
  API
The SetWindowsHookEx function installs an application-
  defined hook procedure into a hook chain. An application
  installs a hook procedure to monitor the system for
  certain types of events. A hook procedure can monitor
  events associated either with a specific thread or with
  all threads in the system.
This function supersedes the SetWindowsHook function.
HHOOK SetWindowsHookEx(
  int idHook, // type of hook to install

  HOOKPROC lpfn, // address of hook procedure
  HINSTANCE hMod, // handle of application instance
  DWORD dwThreadId //identity of thread to install hook for
 );

HTH
Steve Quinn


Stephen,

OK, I took a look and came up with the following. It crashes
  at the MainDLG{self}:Show() line.
METHOD Start() CLASS App
  local lpfn       as ptr
  local ptrHookDLL as ptr
  local ptrHook    as ptr
  local hWnd       as ptr
  local lResult   as logic
  -- Load the DLL that contains the Keyboardproc
  ptrHookDLL:=_VOLoadLibrary("WmHook.DLL")
  if !IsNil(ptrHookDLL)
    -- Load address of the Keyboardproc
    lpfn:=GetProcAddress(ptrHookDLL,String2Psz("NoCEHook"))
    if !IsNil(lpfn)
      -- Set the system wide hook
      ptrHook:=SetWindowsHookEx(WH_KEYBOARD,@lpfn,null,0)
      if IsNil(ptrHook)
        WarningBox{,"","HOOK IS NIL"}:Show()
        << ----- never shows up, then it's ok :)
      endif
    endif
  endif
  -- Find Taskbar and get handle
  hwnd:=FindWindow(String2Psz("Shell_TrayWnd"),null)
  if IsNil(hwnd)
    hwnd:=FindWindow(String2Psz("Shell_TrayHwnd"),null)
    if !IsNil(hwnd)
      lResult:=true
    endif
  else
    lResult:=true
  endif
  --  Hide it if found
  if lResult
    ShowWindow(hwnd,SW_HIDE)
  endif
  MainDLG{SELF}:Show()
  -- Restore Taskbar if it was found
  if !IsNil(hwnd)
    ShowWindow(hwnd,SW_RESTORE)
  endif

  -- Unhook the system wide hook
  if UnHookWindowsHookEx(ptrHook)
    WarningBox{,"","OK REMOVED"}:Show()
    <<--- I never get to see this,
    since the app crashes as soon
    as I press a key. :(
  endif
  -- Unload the DLL
  if !IsNil(ptrHookDLL)
    _VOFreeLibrary(ptrHookDLL)
  endif
RETURN SELF
Now the DLL that contains the function:
Static Function NoCEHook(nCode as int, ;
  wParam as dword, lParam as long) as long CALLBACK
return 0L
That's all I have and I think my problem is right here. It
  might be the CALLBACK statement.
Isn't there a WINHOOK statement ?  I know I saw a _WINCALL
  statement.  What is it used for ?
The help file only lists: CLIPPER, STRICT, PASCAL and
  CALLBACK.
Any ideas ?