CListCtrl bug in WIn95
Steve Rothweiler -- sr@ccrl.nj.nec.com
Monday, May 06, 1996
ENV: VC++ 4.1 Win95
I spent several hours on the phone with Microsoft engineers, and
I thought that this group might benefit from this. The bottom
line is that I got them to admit that there is a (previously
undiscovered) bug in the CListCtrl code in Windows95. I would
like to know if this same bug also occurs in WindowsNT, if anyone
has the time. The bug will be fixed "in the next version of
Windows95", said Microsoft. I asked the obvious question, "When
will that be?". They didn't know. This was back in March.
I know this is a little detailed, but it really isn't all that bad.
If you are using CListView or a CListCtrl in your app, you may want
to try this, because you may run into it in the future. You can
reproduce the bug as follows:
1) Open the database/catalog2 MFC sample, compile it, and run it.
2) File:Open any Access database (.mdb) file. I like to use
database/daoctl/sampdata.mdb in the mfc samples directory.
If you have trouble opening it, make sure it's not read-only.
3) Memorize the ListView data. Note what data is in what columns.
For sampdata.mdb, the Type column has the word TABLE for each item,
and the Qualifier column has the pathname to sampdata for each item.
4) Now make the following modifications to cat2view.cpp. The gist of
this is we are going to delay the addition of column 4 until after
columns 0-3 are added and all their items are added.
A) Comment out line 119 in cat2view.cpp (line numbers may differ):
// control.InsertColumn(4,_T("Remarks"),LVCFMT_LEFT,100,4);
B) Also comment out lines 135-136 inside the while loop in the
CCatalog2Doc::levelTable case:
// control.SetItem(item,4,LVIF_TEXT,
// pDoc->m_pTableset->m_strRemarks,0,0,0,0);
C) Add the following lines immediately after the while loop, but before
the break statement that ends the CCatalog2Doc::levelTable case:
// Now add column 4.
control.InsertColumn(4,_T("Remarks"),LVCFMT_LEFT,100,4);
item = 0;
pDoc->m_pTableset->MoveFirst();
while (!pDoc->m_pTableset->IsEOF())
{
control.SetItem(item,4,LVIF_TEXT,
pDoc->m_pTableset->m_strRemarks,0,0,0,0);
item++;
pDoc->m_pTableset->MoveNext();
}
5) It is easy to see that this should have no effect on the behavior
of the program, but it does! Recompile, run, and open the same
database file you opened before. For sampdata.mdb, the Type column
now has nothing in it, the Qualifier column now has the word TABLE
for each item, and the Owner column which had nothing in it before,
now has the pathnames to sampdata in it!!!
The Microsoft engineers explained that the bug is in the implementation
of InsertColumn(). Even though I added the _LAST_ column to the ListCtrl,
data in previous columns were affected. Since InsertColumn() is
implemented by the operating system, it is a bug in Windows95.
The workaround for me is, when my user wishes to add a new column, I must
delete all the items and column data, then I can reload the entire
ListCtrl. I told them that this is unacceptable for me because I have
many columns (>10) and possibly hundreds of items and it takes over 20
seconds sometimes to reload the ListCtrl (and I have a pretty fast
machine!). They tried for many days to find another workaround, but to
no avail.
They also promised me that they would credit back one of my 2 incidents
that I get for being a Level 2 member of MSDN. The next time I called,
I had no incidents left! I _SCREAMED_ at them. They deserved worse.
Sorry about this, I had to get it off my chest.
--
Steve Rothweiler
sr@ccrl.nj.nec.com Is it just me, or does Microsoft
609-951-2969 _intentionally_ complicate things?
Jeff Lindholm -- JeffL@inter-intelli.com
Thursday, May 09, 1996
[Mini-digest: 3 responses]
ENV: VC++ 4.1, Win95, and NT 4.0
There is a work around, not a very elegant one. If you use an owner
draw list and the lParam is the actual data associated with the row you
can draw the data into the columns as you wish. This is what I do. The
only problem I ran into with this is if you want to switch views you
must either changed the window styles or handle their drawing as well.
The benefit is you can highlight the ENTIRE row not just the first
column.
Jeff
-----From: mikeblas@interserv.com
On Mon, 6 May 96, sr@ccrl.nj.nec.com (Steve Rothweiler) wrote:
>ENV: VC++ 4.1 Win95
Thanks.
>I spent several hours on the phone with Microsoft engineers, and
>I thought that this group might benefit from this. The bottom
>line is that I got them to admit that there is a (previously
>undiscovered) bug in the CListCtrl code in Windows95.
>Since InsertColumn() is
>implemented by the operating system, it is a bug in Windows95.
That is to say, the bug is _not_ in CListCtrl, it is in the Windows common
list control. I think this is far above hair-splitting because people have a
really hard time understanding what part of what program is what library and
where the system starts and ends.
>They also promised me that they would credit back one of my 2 incidents
>that I get for being a Level 2 member of MSDN. The next time I called,
>I had no incidents left! I _SCREAMED_ at them. They deserved worse.
They work as hard as they can in a very stressful environment where they
debug other people's code, try to find problems in software they didn't
write, and then have inappreciative people _SCREAM_ at them all day. It was
probably an honest mistake, but you've made it into some personal vendetta.
What "worse" can they expect? Are you going to fire off hate mail and stuff?
By the way, since you work at NEC, maybe you can answer this: why does my
17-inch NEC monitor have a viewable area so much smaller than NEC? Maybe
I'll call your number and _SCREAM_ at you for a while. You certainly deserve
worse--and you're getting worse, because I'm telling all my friends to buy
Sonys.
.B ekiM
--
TCHAR szDisc[] = _T("These words are my own; I do not speak for Microsoft.");
-----From: Gene Sewell
For what it's worth, you might suggest an alternative way to implement your
list control, namely treat it as a virtual list control.
I am displaying potentially very large databases (w/ cols) using list
controls, and have implemented a virtual list control. Rather than load all
the data into the list control, I only load in the number of lines that are
visible. I then play games with the thumb, positioning it, and responding
to it as if there were many many items in the display. I'm only supporting
report mode, BTW.
If you were to do this approach, there would be no 20 sec reload - it would
be done instantly....
Just a suggestion, since it sounds like the current system is unusable.
Gene
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