[DUG] Access violation in TTntCustomListView (Delphi 7)

[Jolyon Smith]

What version of TNT are you using ?

There is nothing intrinsically wrong with the line on which the error is
occurring, which suggests that the problem is with the parameters
involved.  Given that it is a write op to a NIL address, this points the
finger at the destination of the WStrLCopy()... the pszText member of the
item data.

There is potential for the pszText parameter to be invalid, if the
LVIF_TEXT flag is not set in the notification mask.  According to the
community additions on the MSDN ref for the LVN_DISPINFO notification (
http://msdn.microsoft.com/en-us/library/windows/desktop/bb774818(v=vs.85).aspx),
this is specifically the case on Windows 8 when list selection changes, as
would occur when keying up/down through the list, for example.

So far, everything seems to point in the same direction....


However, the code you have quoted above is conditional on the LVIF_TEXT
flag being set, but there is code that precedes this in TNT which invokes
the inherited implementation of the CNNotify handler, removing and
re-instating the LVIF_TEXT flag in the process.

The reason I ask about the version you are using is that in the version I
am looking at (2.3.0) this preceding code appears to handle the LVIF_TEXT
flag correctly, only re-applying the LVIF_TEXT flag if it was originally
set.  But I wonder if you have some version of the TNT code which perhaps
contains a flaw in this area and is adding this flag when it shouldn't ?

Or is it possible that your copy of the source has been modified from the
TNT original in a way that might have introduced such a flaw ?


It might be helpful to post the entire LVN_GETDISPINFOW handler from the
CNNotify() method, to be sure.


On 3 November 2014 20:06, Ross Levis <ross at stationplaylist.com> wrote:

> I hope someone can help.  I’m using the freeware TNT controls with D7 for
> a TTntListView component.  This is working fine for many users but one user
> experiences a crash when simply using the keyboard to move up and down the
> listview.  He is using Win8 64-bit as I do here, but I can’t duplicate it.
>
>
>
> It is a virtual listview using OnData.  Here is a portion of a MadExcept
> log.  Can provide more if required.
>
>
>
> exception message : Access violation at address 0050DA73 in module
> 'SPLStudio.exe'. Write of address 00000000.
>
>
>
> main thread ($d88):
>
> 0050da73 SPLStudio.exe TntWideStrUtils   180  +10 WStrLCopy
>
> 0053e20e SPLStudio.exe TntComCtrls      2104  +46
> TTntCustomListView.CNNotify
>
> 004f304f SPLStudio.exe Controls         4645  +53 TControl.WndProc
>
> 004f6d5e SPLStudio.exe Controls         6342  +33 TWinControl.WndProc
>
> 004c04a5 SPLStudio.exe ComCtrls        14815  +12 TCustomListView.WndProc
>
> 0053dee4 SPLStudio.exe TntComCtrls      2023  +98
> TTntCustomListView.WndProc
>
> 00539335 SPLStudio.exe TntControls       666  +19
> TWinControlTrap.WindowProc
>
> 004f2d5a SPLStudio.exe Controls         4552   +5 TControl.Perform
>
> 004f6f20 SPLStudio.exe Controls         6388   +6 DoControlMsg
>
> 004f772f SPLStudio.exe Controls         6579   +1 TWinControl.WMNotify
>
> ...
>
> Code in TntComCtrls.pas where it crashes updating a list item caption...
>
>
>
>       // handle any text info
>
>       with PLVDispInfoW(NMHdr)^.item do
>
>       begin
>
>         if (mask and LVIF_TEXT) <> 0 then
>
>         begin
>
>           Item := GetItemW(PLVDispInfoW(NMHdr)^.item);
>
>           if iSubItem = 0 then
>
> >>>>>  WStrLCopy(pszText, PWideChar(Item.Caption), cchTextMax - 1)
>
>           else begin
>
>             with Item.SubItems do begin
>
>               if iSubItem <= Count then
>
>                 WStrLCopy(pszText, PWideChar(Strings[iSubItem - 1]),
> cchTextMax - 1)
>
>               else pszText[0] := #0;
>
>             end;
>
>           end;
>
>         end;
>
>       end;
>
>
>
> Any ideas appreciated.
>
>
>
> Thanks,
>
> Ross,
>
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