Hi.

I want to control the execution of a loop with a checkbox. If the checkbox is checked the loop should run, if it is unchecked no action. I tried this with onClick:

CheckBox.Click(Sender:TObject);
begin
  repeat
    Some Action …
    Form.Update;
  until (CheckBox.State  checked)
end;

The loop starts, but i cannot click the Checkbox again for switching off. How to do it? Is it possible without threads?

Michael.

CheckBox.Click(Sender:TObject);
begin
  repeat
    Some Action …
    Appication.ProcessMessage;
  until (CheckBox.State  checked)
end;

2016-08-10 10:56 GMT-03:00 Schindler Karl-Michael <

On Wed, Aug 10, 2016 at 9:56 AM, Schindler Karl-Michael <

thanks,
Dmitry
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lazarus-ide.org/pipermail/lazarus/attachments/20160810/5d45cc44/attachment.html>

Besides the typo ;-) Application.ProcessMessages did the trick. Thanks.

Hi,

Besides the typo ;-) Application.ProcessMessages did the trick. Thanks.

Don't know if this is an issue anymore, it was in Delphi some time ago so you may want to check:

It used to be Application.processmessages pegged cpu to 100%. The alternative "application.handlemessage" may be a bit slower but much nicer on the cpu. Again, don't know if this is an issue in Lazarus.

A loop with Application.ProcessMessages with 100% CPU usage will also use up your battery on a laptop or mobile device. An easy way to improve that is to put sleep(10) into the loop.

Here a short explanation of the alternative I use most of the time: http://codenewsfast.com/cnf/article/0/permalink.art-ng1824q786

You can find the above link and other things here: http://turbocontrol.com/APro.htm

Regards,
Paul
www.ControlPascal.com

HandleMessages calls ProcessMessages and then sleeps til a new message. This is Delphi compatible and by design.

100% cpu without need is bad coding.

Mattias

Schindler Karl-Michael wrote

I want to control the execution of a loop with a checkbox. If the checkbox is checked the loop should run, if it is unchecked no action. I tried this with onClick:

Something like that should never be done in an "Event driven" system like a Lazarus application.

Each event should be finished (ad the handler procedure exited) as fast as possible.

So you should exit the procedure when the check box is not checked and start a new execution in the "CheckBox1Change" event.

-Michael

Michael Schnell wrote

Each event should be finished (ad the handler procedure exited) as fast as possible.

If you extend this (into ludicracy) this would mean that exch event should fire a new thread that rubs the code needed and then exit... ;-)

Bart

Well probably if the event is required to do something useful but time-consuming (like launching a long long calculation) while the GUI (thread) needs to be responsive (e.g. report on progress, maybe abort the calculation or change parameters in-flight)

Bart

el es

Bart wrote

If you extend this (into ludicracy) this would mean that exch event should fire a new thread that rubs the code needed and then exit... ;-)

Depending on the exact task in question this indeed might be perfectly viable.

But doing a busy loop (resulting in 100% do-nothing CPU) on behalf of a GUI switch IMHO is not really appropriate ever.

-Michael