Lazarus

Programming => LCL => Topic started by: jwdietrich on June 29, 2019, 06:56:11 pm

Title: Cross-platform way to get and toggle the Num Lock state
Post by: jwdietrich on June 29, 2019, 06:56:11 pm

Is there a cross-platform method for reading and setting the Num Lock state on the numeric keypad available? My application should activate Num Lock on launch or activation and restore the pre-launch state on terminating or when being deactivated.

The solution should be cross-platform compatible to Windows and Linux (macOS not necessary, where Num Lock is always on).

Title: Re: Cross-platform way to get and toggle the Num Lock state
Post by: jwdietrich on July 02, 2019, 10:49:34 pm

Well, I think it has reasons that this thread doesn't get a reply.

I learned that setting the num lock state requires administrating privileges and isn't part of the userland API, at least in Windows (see e.g. https://stackoverflow.com/questions/25724740/getting-and-setting-numlock-state-in-lazarus (https://stackoverflow.com/questions/25724740/getting-and-setting-numlock-state-in-lazarus)). In my opinion, this doesn't make sense, since this is nothing than an issue of the user interface, but this decision has been made long ago.

I now changed the design of my app, so that it reads the num lock state and provides a warning if num lock is deactivated.

For those who are interested, the following method changes the colour of a small circular shape (NumLockIndicator to be similar to a little LED) to red or green depending on the num lock state:

Code: Pascal  [Select][+][-]

1. procedure TMainForm.IndicateNumLockState(Sender: TObject);
2. begin
3.   {$IF DEFINED(LCLcarbon) or DEFINED(LCLCocoa)}
4.     NumLockIndicator.visible := false;
5.   {$ELSE}
6.   if Odd(GetKeyState(VK_NUMLOCK)) then
7.   begin
8.     NumLockIndicator.Brush.Color := clLime;
9.     NumLockIndicator.Hint := 'Num Lock is activated. You can enter numbers via the numeric keypad.';
10.   end
11.   else
12.   begin
13.     NumLockIndicator.Brush.Color := clRed;
14.     NumLockIndicator.Hint := 'Num Lock is deactivated. Numbers cannot be entered via the numeric keypad.';
15.   end;
16.   {$ENDIF}
17. end;

This code is inspired by https://forum.lazarus.freepascal.org/index.php?topic=12143.0 (https://forum.lazarus.freepascal.org/index.php?topic=12143.0).