[DUG] TListitems disappearing and reappearing causing access violations

[Kyley Harris]

If that was the case.. then its unlikely to happen midstream during a very
small short procedure call. Especially if that procedure call is a user
initiated one.

if that is the case.. its extremely simple to test this with remote desktop
and some logging of the construction/destruction of the list items.


On Tue, Apr 9, 2013 at 11:29 PM, Ross Levis <ross at stationplaylist.com>wrote:

> I’ve had someone suggest this elsewhere…****
>
> ** **
>
> *The user connects a monitor to a laptop, or connects remotely via
> terminal services.
> Basically, anything that changes the display resolution has that kind of
> consequences.*
>
> ** **
>
> I have seen a TeamViewer in one of the many screen shots.  So I guess
> Windows is recreating the windows and allocating new handles to the list
> items as I thought.  I’ll check with them if the crashes coincide with use
> of TeamViewer.****
>
> ** **
>
> Ross.****
>
> ** **
>
> *From:* Ross Levis [mailto:ross at stationplaylist.com]
> *Sent:* Tuesday, 9 April 2013 11:17 p.m.
> *To:* 'NZ Borland Developers Group - Delphi List'
> *Subject:* RE: [DUG] TListitems disappearing and reappearing causing
> access violations****
>
> ** **
>
> The list is populated by the software.  It’s still in Delphi 7.****
>
> ** **
>
> No threads are deleting any items.  Only the main thread adds and removes
> items.****
>
> ** **
>
> There is no one procedure this has occurred in.  It can work for 2 days
> and suddenly this happens in a random procedure that accesses a list item.
> ****
>
> ** **
>
> In this particular case, it is in a procedure where one specific listitem
> is sent as a parameter.****
>
> ** **
>
> Here are some of the relevant lines of code in the procedure being
> executed.****
>
> ** **
>
>     if Item <> nil then****
>
>     begin****
>
>       if Item.Selected then UpdateButtons;****
>
>        …****
>
>       Item.ImageIndex := 8;****
>
>     end;****
>
> ** **
>
> There are no deletions in the procedure.****
>
> ** **
>
> The Item.Selected test works fine but Item.ImageIndex := 8 crashes at
> TListItem.SetImage with an access violation.****
>
> ** **
>
> The item existed and then no items exist based on the screen shot.****
>
> ** **
>
> I’ve been having to put validations all over the place like this…****
>
> if ListView.Items.IndexOf(Item) >= 0 then Listitem.ImageIndex := 8.****
>
> ** **
>
> This user has had a crash where it does this validation up the procedure
> somewhere which validated, but further down it will be accessing Item.Index
> and this crashes.****
>
> ** **
>
> It’s a nightmare.  I’m wondering if it could be corrupt RAM in the PC or
> something.****
>
> ** **
>
> Cheers,****
>
> Ross.****
>
> ** **
>
> *From:* delphi-bounces at listserver.123.net.nz [
> mailto:delphi-bounces at listserver.123.net.nz<delphi-bounces at listserver.123.net.nz>]
> *On Behalf Of *Kyley Harris
> *Sent:* Tuesday, 9 April 2013 10:33 p.m.
> *To:* NZ Borland Developers Group - Delphi List
> *Subject:* Re: [DUG] TListitems disappearing and reappearing causing
> access violations****
>
> ** **
>
> without seeing the 10lines above, and whats inbetween (if you were being
> literal) its very hard to say. ****
>
> The only time I've ever had something dissapear from a list is when I
> deleted it though a callback, method, thread etc.. or freeing something. *
> ***
>
> what version of delphi is the code now? How does the list get populated or
> edited by the application.. ****
>
> I'd start by looking at how many locations of code insert or delete the
> list items, and verify none are being called while your procedure is
> executing its for-loop, (assuming the access violation is an index based
> one because of the list count change)****
>
> ** **
>
> ** **
>
> On Tue, Apr 9, 2013 at 10:21 PM, Ross Levis <ross at stationplaylist.com>
> wrote:****
>
> Wondering if anyone has any ideas.****
>
>  ****
>
> I've had this problem a long time from when I started writing an app about
> 7 or 8 years ago, but it happens so rarely it's not usually an issue. But
> one user in particularly is regularly sending me MadExcept reports which
> either have access violation errors or "the application appears to be
> frozen". In all cases it's during an access of a TListItem which was
> perfectly valid 10 lines of code up a procedure but suddenly doesn't exist.
> ****
>
>  ****
>
> The screenshot created at the same time shows the ListView has no visible
> items, but I know for a fact there are 30 or more items in the list. I
> believe sometimes the items visually disappear and reappear shortly
> afterwards, like a Desktop refresh.****
>
>  ****
>
> I think I've heard something about Windows recreating the window handles
> or some such thing. I don't understand why it would do so. There are no
> changes to the listview that would require re-creating the window.****
>
>  ****
>
> Any ideas?****
>
>  ****
>
>
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>
>
> --
> Kyley Harris
> Harris Software
> +64-21-671-821 ****
>
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-- 
Kyley Harris
Harris Software
+64-21-671-821
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