Alan,
Your problem intrigued me, so I tested it myself. I found the same
behavior, and started looking for the cause. I found it, however, I'm not
sure it's something that can ( or even should be ) fixed. I'll let you and
Jason decide that. I'm only starting to get familiar with the innards of
IBO, so someone who knows the code in and out should look at it. I'll just
sum up what I figured out...

The problem lies in the min/max range of the scroll bar. Until the
recordcount is known, the UpdateScrollbar method of the grid falls into the
else clause (see below:

if CursorRecordCountValid then
begin
[SNIP]
end
else
begin
//THE CODE FALLS IN HERE UNTIL THE RECORDCOUNT IS KNOWN

if not BufferHasBof then Dec( SINew.nMin, SINew.nPage div 2 + 1 );
if not BufferHasEof then Inc( SINew.nMax, SINew.nPage div 2 + 1 );
end;

These "guess-timated" values of SINew.nMin and nMax are then used at the
bottom of the
function to set the scrollbar's parameters with
SetScrollInfo( Handle, SB_VERT, SINew, True );

To verify that this is the cause, I pumped a dummy table with 500000 single
field rows (an integer, with vals from 0 to 499999), then pointed an IB_grid
at it with thumbtracking enabled. Then I performed your procedure of
dragging the
thumb around. If you pay attention to the integer values (the whole reason
I used an integer field), every
time you drag the thumb to the bottom and let go, the grid brings in a new
set of rows roughly equal to half the
number of visible grid rows. If you force the query to fetch all 500000
rows, ( i used a separate button's click event ),
then, voila! Drag the thumb up and down, let go anywhere, and it behaves
just like it should from then on. Therefore,
the problem lies in that the query doesn't know how many actual data rows
there are until you pull them all, so the scrollbar's min and max vals
aren't being set correctly, which means that windows can't pass the correct
thumbposition to the
grid in the WMVSCROLL message handler...

I hope this helps you guys figure out a viable solution, since I agree that
to a customer, this could be confusing... What you could do in the interim
is just force a fetchall up front when using thumbtracking.

Brian

> -----Original Message-----
> From: Jason Wharton [mailto:jwharton@...]
> Sent: Thursday, December 19, 2002 1:31 PM
> To: IBObjects@yahoogroups.com
> Subject: Re: [IBO] TIB_Grid ThumbTrack Q
>
>
> I don't follow this 100%. Will you please be more descriptive?
>
> Jason Wharton
> CPS - Mesa AZ
> http://www.ibobjects.com
>
> -- We may not have it all together --
> -- But together we have it all --
>
>
> ----- Original Message -----
> From: "Alan McDonald" <alan@...>
> To: <IBObjects@yahoogroups.com>
> Sent: Thursday, December 12, 2002 12:04 AM
> Subject: [IBO] TIB_Grid ThumbTrack Q
>
>
> > When Thumbtrack is set to True, you can scroll the grid to the first
> record
> > by tracking the scroll bar to the top. But tracking the scrollbar to the
> > bottm leaves the cente cell of the grid highlighted instead of the last
> > record/cell.
> >
> > Alan
>
>
>
>
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