Is there a bug in TListBox?
lazarus / 31-LCL

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vfclists · 2010-05-03 19:10

This code is to scan the list of selected items in a List box and add
them to a string list. It crashes when it gets to an unselected item.

Am I doing something wrong here, or is it a known bug?

Code: [Select]procedure TutilitiesInterfaceForm.GetEventsList(list:
TStringList);
var
 i :integer;
begin
  for i := 0 to lbEventsToMonitorA.Items.Count - 1 do
  begin
    if lbEventsToMonitorA.Selected[i] = true then
      list.Add(lbEventsToMonitorA.Items[i]);
  end;
end;

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Marc · 2010-05-03 21:56

on what line does it crash ?
This code should work.

ps.
Code: [Select]if lbEventsToMonitorA.Selected[i] = true then
is the same as
Code: [Select]if lbEventsToMonitorA.Selected[i] then
Selected[] already returns a boolean, no need to compare it against
another boolean

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vfclists · 2010-05-03 23:45

It crashes on this line:
Code: [Select]if lbEventsToMonitorA.Selected[i] = true then
and the crash occurs when the item is not selected, ie always crashes
on the first on selected item.

Quote from: Marc on May 03, 2010, 11:56:05 pmon what line does it
crash ?
This code should work.

ps.
Code: [Select]if lbEventsToMonitorA.Selected[i] = true then
is the same as
Code: [Select]if lbEventsToMonitorA.Selected[i] then
Selected[] already returns a boolean, no need to compare it against
another boolean

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eny · 2010-05-04 04:46

Just a thought: is your listbox populated, the first time you call
'GetEventsList'?

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Marc · 2010-05-04 06:50

Quote from: eny on May 04, 2010, 06:46:43 amJust a thought: is your
listbox populated, the first time you call 'GetEventsList'?

if not populated, "for i := 0 to lbEventsToMonitorA.Items.Count - 1
do" wont do anything.

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Marc · 2010-05-04 06:51

Quote from: vfclists on May 04, 2010, 01:45:58 amIt crashes on this
line:
Code: [Select]if lbEventsToMonitorA.Selected[i] = true then
and the crash occurs when the item is not selected, ie always crashes
on the first on selected item.

is lbEventsToMonitorA visible ?

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vfclists · 2010-05-04 07:17

It is populated at design time. As I said, it crashes when the index
hits the first unselected item.

Quote from: eny on May 04, 2010, 06:46:43 amJust a thought: is your
listbox populated, the first time you call 'GetEventsList'?

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vfclists · 2010-05-04 07:19

Quote from: Marc on May 04, 2010, 08:51:16 amQuote from: vfclists on
May 04, 2010, 01:45:58 amIt crashes on this line:
Code: [Select]if lbEventsToMonitorA.Selected[i] = true then
and the crash occurs when the item is not selected, ie always crashes
on the first on selected item.

is lbEventsToMonitorA visible ?

It is visible, fully upfront. Something appears to be wrong with code
generation.

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Bart · 2010-05-04 14:06

Similar code:
Code: [Select]var
  i: Integer;
begin
  for i := 0 to listbox1.Items.Count - 1 do
    if listbox1.Selected[i] then
      debugln('Selected[',dbgs(i),'] = True, Value =
',Listbox1.Items[i])
    else
      debugln('Selected[',dbgs(i),'] = False, Value =
',Listbox1.Items[i]);
end;

runs perfectly fine here.

Q: Is list assigned (created) when you pass it to the procedure?

Bart

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vfclists · 2010-05-05 05:16

I have checked and the code is correct. There were problems further
down in the source code, but the debugger was executing them without
moving the highlight to them.

The highlight would be in one place where as the code was executing
somewhere else. Is that a known feature? (Lazarus 0.9.28 Windows)

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Marc · 2010-05-05 19:46

Only if source and exe are out of sync. (iow, you edited the source
without recompilation)