Delphi application - Block windows-key (Start) on Windows 8

Question

I' programming a Delphi application. My goal is to cover ALL screen with my application to force user to fill my form. Application will be run as scheduled task.

My problem is, that normally, Windows does not allow applications to block other users action.

In Windows 7 I can run my application as scr file (screen saver), with no title bar and set StayOnTop. In this case, other application even if visible on "Window key" (start), stays behind my application, so my goal is reached. Unfortunately, in Windows 8 this solution does not work because "window key" shows start screen, when I can run anything and this "anything" stays on top.

I tried some trick with code below, but without success.

  h := FindWindowEx(FindWindow('Shell_TrayWnd', nil),0,'Button',nil);
  ShowWindow(h,0); 
  Windows.SetParent(h,0);

How to block 'window key' (start button) action in the entire Windows 8 system?

Answer 1

I didn't test it on windows 8, but in principle one can use a keyboard hook to discard the key-press.

Something similar to the following:

const   
    WH_KEYBOARD_LL   =   13;
    LLKHF_ALTDOWN    =   $00000020;
    LLKHF_INJECTED   =   $00000010;

type
    tagKBDLLHOOKSTRUCT   =   record
        vkCode:   DWORD;
        scanCode:   DWORD;
        flags:   DWORD;
        time:   DWORD;
        dwExtraInfo:   DWORD;
      end;
    KBDLLHOOKSTRUCT   =   tagKBDLLHOOKSTRUCT;
    LPKBDLLHOOKSTRUCT   =   ^KBDLLHOOKSTRUCT;
    PKBDLLHOOKSTRUCT   =   ^KBDLLHOOKSTRUCT;

var
    hhkLowLevelKybd:   HHOOK;

function LowLevelKeyBoardProc(nCode:   Integer;   awParam:   WPARAM;   alParam:   LPARAM):   LRESULT;   stdcall;
var
    fEatKeyStroke:   Boolean;
    p:   PKBDLLHOOKSTRUCT;
begin
    fEatKeystroke   :=   False;
    if active and(  nCode   =   HC_ACTION)   then
    begin
        case   awParam   of
            WM_KEYDOWN,
            WM_SYSKEYDOWN,
            WM_KEYUP,
            WM_SYSKEYUP:
                begin
                    p   :=   PKBDLLHOOKSTRUCT(alParam);
                    if DisableWinKeys then
                     begin
                      if p^.vkCode   =   VK_LWIN
                        then fEatKeystroke   :=   True;
                      if p^.vkCode   =   VK_RWIN
                        then fEatKeystroke   :=   True;
                     end;
                end;
        end;
    end;
    if   fEatKeyStroke   then
        Result := 1
    else
        Result := CallNextHookEx(hhkLowLevelKybd, nCode, awParam, alParam);
end;

procedure InstallHook;
begin
  if hhkLowLevelKybd <> 0 then exit;
  hhkLowLevelKybd := SetWindowsHookEx(WH_KEYBOARD_LL, @LowLevelKeyboardProc,   hInstance,   0);
end;

procedure UninstallHook;
begin
  if hhkLowLevelKybd = 0 then exit;
  UnhookWindowsHookEx(hhkLowLevelKybd);
  hhkLowLevelKybd := 0;
end;