[lazarus] CheckListBox can't store objects with items in win32 interface

[Marc Weustink]

At 21:14 8-12-2003, Vincent Snijders wrote:
>On Mon, 08 Dec 2003 00:30:56 +0100
>Marc Weustink <marc at dommelstein.net> wrote:
>
> > At 22:23 7-12-2003, Vincent Snijders wrote:
> > >On Sun, 07 Dec 2003 18:41:49 +0100
> > >Marc Weustink <marc at dommelstein.net> wrote:
> > >
> > > > At 10:47 7-12-2003, Vincent Snijders wrote:
> > > > >Hi,
> > > > >
> > > > >While trying to get the debug options dialog working, I noticed
> > > > >that the win32 interface doesn't store the objects associated
> > > > >with a list item in a CheckedListBox (or ListBox).
> > > > >
> > > > >While implementing this the obvious way with LB_SETITEMDATA. This
> > > > >works for TListBox, but not for TCheckListBox, because
> > > > >TCheckListBox stores it Checked property in the item data.
> > > >
> > > > Yep.
> > > >
> > > > >Any suggestions to solve this? Storing a heap-allocated record
> > > > >with object and selected fields in the item data is one
> > > > >possibility, but I fear the bookkeeping involved. Any suggestions
> > > > >are wellcome.
> > > >
> > > > I had the samme problem when I introduced the CheckList. Delphi
> > > > uses the TCheckListBoxDataWrapper class to handle this. We can do
> > > > it the same way, but like you said, you need some bookkeeping.
> > > > Another way is to move the checkstate to the interface, so that
> > > > Item.Dat is just userdata. The TCheckListBoxDataWrapper class
> > > > isn't published, so I have no problems with that.
> > >Maybe I don't understand you, but at the moment checkstate is stored
> > >in the interface, together with item text and item object. So where
> > >do you want to move the checkstate to?
> > >Do you mean to move the storage of checked state to the LCL?
> >
> > No, I was just wondering why the checked state was stored as data. The
> > only thing I could think of was that it wasn't stored (or isn't
> > accessible) through the interface. So if there is a function like
> > LCLIsItemChecked, I see no reason to store it in the LCL as well.
> > (Ehm, I don't know if there is a function like that, I've no access to
> > all source at the moment)
>FYI, at the moment checked state is already stored in the interface and
>set and retrieved by the LCL with the LM_CLB_SETCHECKED and
>LM_CLB_GETCHECKED messages.

We might want to change these to direct calls in the future :)

>The Items stringlist is also stored in the interface. The problem I have
>now is, that for each item in a checked listbox three things need to be
>stored: string, object and checkstate. The win32 api has only place for
>2: string (item text) and object (item data).
>If you don't want to move the storage of checkedstate to the LCL, I see
>no other way than to store the checkedstate and the object together in
>item data, which will need some taking care to prevent memory
>leaks when deleting items or clearing the list.

Thats true. IMO this is an interface issue. So for win32 the item data is 
in fact a record with a data pointer and a checked bool.

>If you see another way, please let me know. Otherwise I will implement
>it this way this week.

AFAIK there is no other option. And indeed we have to take care of 
releasing data on WM_DESTROY and romoving items.
Maybe we should use data in a mixed way. Initially only as bool (0 or 1) 
and as soon as Data is used, as a pointer to a rec.

Marc