|Disabling The System Keys from Your Application|
When my application is running, I'd like to prevent users from using Ctrl-Alt-Del and Alt-Tab. What's the best way to do this?
This is pretty quick one... The best way I've seen yet is to trick Windows into thinking that a screen saver is running. When Windows thinks a screensaver is active, Ctrl-Alt-Del and Alt-Tab (Win95 only for this) are disabled. You can perform this trickery by calling a WinAPI function, SystemParametersInfo. For a more in-depth discussion about what this function does, I encourage you to refer to the online help.
In any case, SystemParametersInfo takes four parameters. Here's its C declaration from the Windows help file:
BOOL SystemParametersInfo( UINT uiAction, // system parameter to query or set UINT uiParam, // depends on action to be taken PVOID pvParam, // depends on action to be taken UINT fWinIni // user profile update flag );
For our purposes we'll set uiAction to SPI_SCREENSAVERRUNNING, uiParam to 1 or 0 (1 to disable the keys, 0 to re-enable them), pvParam to a "dummy" pointer address, then fWinIni to 0. Pretty straight-forward. Here's what you do:
To disable the keystrokes, write this:
SystemParametersInfo(SPI_SCREENSAVERRUNNING, 1, @ptr, 0);
To enable the keystrokes, write this:
SystemParametersInfo(SPI_SCREENSAVERRUNNING, 0, @ptr, 0);
Not much to it, is there? Thanks to the folks on the Borland Forums for providing this information!
|Copyright © The Delphi Corner 2001 All Rights Reserved|