public BarcodeHandler()
 {
     _buffer    = new StringBuilder(128);
     _hookFlag  = false;
     _hookValid = false;
     _procHook  = new delLowLevelKeyboardProc(HookHandleProc);
     _hHook     = SetHook();
     if (_hHook == 0)
     {
         throw new CouldntHookException();
     }
 }
 private static extern long SetWindowsHookEx(int idHook,
                                             delLowLevelKeyboardProc lpfn, IntPtr hMod, uint dwThreadId);