Checkbox functionality?
lazarus / 31-LCL

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Ruptor · 2013-03-03 11:35

I wanted to make two check boxes always be in the opposite state and
thought it was a straightforward task but my first attempt didn't
work.  It took two clicks to get a checkbox to turn on but the other
checkbox was switched off on the first click. My logic was that if a
checkbox is clicked it is set true so setting the other one to false
would uncheck it. Clearly my logic is wrong but why?
Code: [Select]// initialised to
COGchk.checked:=false;

procedure TForm1.COGchkChange(Sender: TObject);
begin
  EMAchk.checked:=false;
end;

procedure TForm1.EMAchkChange(Sender: TObject);
begin
  COGchk.checked:=false;
end;
 I fixed the problem by using.
Code: [Select]procedure TForm1.COGchkChange(Sender: TObject);
begin
  EMAchk.checked:=not COGchk.checked;
end;

procedure TForm1.EMAchkChange(Sender: TObject);
begin
  COGchk.checked:=not EMAchk.checked;
end;

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taazz · 2013-03-03 11:42

You have just described the radio buttons, and to top it you do not
take in to account what happens wen more than 2 check boxes are used
and one is unchecked.

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Ruptor · 2013-03-03 12:01

Do you mean I should be using the radio buttons instead? I just
thought having a tick positioned above what I wanted to show as
selected looked better.
I figured out what the problem was with my original code. I shouldn't
have used "change" because of course when one change alters the other
box the change is triggered and the routine is called for the other
box. A bit of a recursive situation so I should be using "OnClick"
instead.

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taazz · 2013-03-03 12:07

yes radio buttons would be hat I would use doesn't matter how or where
they will appear.
As for the problem I wouldn't use the click event you ignoring the the
keyboard. use the change and have a flag set eg.
Code: [Select]procedure TForm1.COGchkChange(Sender: TObject);
begin
  IF Fchanging then exit;
  FChanging := true;
  try
    EMAchk.checked:=not COGchk.checked;
  finally
    FChanging := false;
  end;
end;

procedure TForm1.EMAchkChange(Sender: TObject);
begin
  IF Fchanging then exit;
  FChanging := true;
  try
    COGchk.checked:=not EMAchk.checked;
  finally
    FChanging := false;
  end;
end;

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Ruptor · 2013-03-03 12:51

OK Thanks for the help I will use it.

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Ruptor · 2013-03-03 13:26

I had the "OnClick" already coded so I tested it but it had the
recursive problem as well. A change of check state is seen as a click
of the checkbox which seems wrong to me. So it doesn't matter which
method is used the other checkbox routine will get called
unnecessarily and is a waste of cpu time. Perhaps I should use mouse
and keypress instead but the value change might cause these to run
too.