[API Review] RT-24916 - TableView.scrollTo(TableColumn)

John Hendrikx hjohn at xs4all.nl
Mon Feb 4 22:57:18 PST 2013

On 4/02/2013 21:02, Jonathan Giles wrote:
> This is a fair comment: scrollTo has been designed with a 
> 'fire-and-forget' approach in mind, but I would be loath to add a 
> means of requesting a self-correcting scrollTo function. Wouldn't a 
> suitable workaround be to call scrollTo after the image loading has 
> completed in all cells?
The problem is that image loading occurs in the background, and it is 
not really predictable when all of them are completed.  In my example 
application, these images are loaded from a database (when cached) or 
from the internet when not.  It may take 10 seconds before one has been 
loaded if it wasn't cached.  Waiting that long before I restore the 
position of the view for the user is not acceptable.  Also, calling 
scrollTo may trigger more image loading (as new cells come into view), 
so I'd have to call it in a loop until no more images are getting loaded...

I realize that self-correcting the position seems wierd, but on the 
other hand, why is the control adjusting position when some cell changes 
height?  Should the View control not take every effort to stay in the 
same position?  In other words, if my last interaction with the View 
class was to tell it "show me cell 313 nicely centered", and then cells 
304-312 change their height, should they not simply be pushed up and out 
of view and keep my cell 313 centered?

I think it should store its "position" not as some absolute Y coordinate 
(which would change whenever any intermediate cell changes height), but 
more relative to the cell.  ie. the position is cell 313, centered at 
45% down from the top of the control.  That way when a cell changes, it 
will try to keep the position stable.

I cannot predict when image loading will happen, nor when it will 
finish.  Even if I could, I'd probably have to call scrollTo in a loop 
for a few times as it would not be acceptable to wait calling it.  
Also... as soon as I do call it, other cells are likely to scroll into 
view, triggering more image loading...

> Regarding a lower-level API for exact positioning, please file a jira 
> tweak request.
I've filed http://javafx-jira.kenai.com/browse/RT-28192


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