I am not understanding something...

Question

Well, actually there are many things I don't understand. Like, for example, how my fellow american citizens can be stupid enough to sign up for another four years of...oh, never mind, what's the point?
What's really bothering me at the moment is this "feature", which I have been completely incapable of implementing successfully. It seems simple, which is exactly why I am annoyed by my continued failure to do it properly.
All I want (ok, not ALL I want, but certainly something I want) is to have a real-time list of data automatically keep itself scrolled to the most current entry. You know, kind of like you'd expect it to do in any reasonable gui, right?
I figured, no problem. A JList inside a JScrollPane. Then a function to add data to the JList and max out the vertical scrollbar. Launch n+1 threads which all reference the "parent" object in order to update the list.
Well, even before implementing this, I knew there was a small problem. For the "classic" feel, the list should only autoscroll if you aren't using the list at the time - like scrolling up or looking at some other section of the list. But, one thing at a time.
Immediate problem. It doesn't work as expected. Much of the time, the scrollbar doesn't go all the way to the bottom, but instead stays just above the last one or two lines.
Another problem. Sometimes the list just flat out goes BLANK - no scrollbar, no nothing. It only comes back when something else is added to the list.
Knowing a little something about Swing, I figured it was possible the add-to-list command wasn't finishing in time for the autoscroll command to do it's job properly. In other words, the scrollbar was maxing out, then the items were appearing in the list. So I used SwingUtilities.invokeLater() in an attempt to "delay" the scrolling.
No luck. It might have had some effect, but not enough. I tried putting a sleep timer in the invokeLater(), but that just paused my whole application.
I'd be happy to provide code etc if anyone cares (originally posted at http://forum.java.sun.com/thread.jspa?threadID=579946 but tweaked since then), but what I really want is a solution. I.E. I'm not sure I'm even going about this problem in the right way, which is why I defined it in such general terms up above. If it can/should be done without a JList or JScrollPane, that's fine.

Answer 1

Well, actually there are many things I don't
understand. Like, for example, how my fellow american
citizens can be stupid enough to sign up for another
four years of...oh, never mind, what's the point?Sorry,. that's a topic for a different thread... :-)
http://forum.java.sun.com/thread.jspa?threadID=578435&start=0&tstart=0
What's really bothering me at the moment is this
"feature", which I have been completely incapable of
implementing successfully. It seems simple, which is
exactly why I am annoyed by my continued failure to
do it properly.I know the feeling.
All I want (ok, not ALL I want, but certainly
something I want) is to have a real-time list of
data automatically keep itself scrolled to the most
current entry. You know, kind of like you'd expect it
to do in any reasonable gui, right?Sure.
I figured, no problem. A JList inside a JScrollPane.
Then a function to add data to the JList and max out
the vertical scrollbar. Launch n+1 threads which all
reference the "parent" object in order to update the
list.Sounds logical (or a JTable, but same difference).
Well, even before implementing this, I knew there was
a small problem. For the "classic" feel, the list
should only autoscroll if you aren't using the list
at the time - like scrolling up or looking at some
other section of the list. But, one thing at a time.Could be annoying to the user, yeah.... How do you know, except to know that focus is on the list, in which case you don't scroll, and thus you'd have to explicitly have focus leave the list to get back to "normal".
Immediate problem. It doesn't work as expected. Much
of the time, the scrollbar doesn't go all the way to
the bottom, but instead stays just above the last one
or two lines.What if you try:
list.scrollRectToVisible(new Rectangle(0, list.getSize().height-1, 1, 1));
Of course, setVisibleIndex() or whatever should work.
Another problem. Sometimes the list just flat out
goes BLANK - no scrollbar, no nothing. It only comes
back when something else is added to the list.Sounds like a thread concurrency problem.
Knowing a little something about Swing, I figured it
was possible the add-to-list command wasn't finishing
in time for the autoscroll command to do it's job
properly. In other words, the scrollbar was maxing
out, then the items were appearing in the list. So I
used SwingUtilities.invokeLater() in an attempt to
"delay" the scrolling.I would guess you aren't using invokeLater() in the right place, that place being in the code that updates the list model, which in turn, tells the list view to update itself. And that might be coupled with a synchronization problem as well, depending on how you are updating the list model.
No luck. It might have had some effect, but not
enough. I tried putting a sleep timer in the
invokeLater(), but that just paused my whole
application.right.
I'd be happy to provide code etc if anyone cares
(originally posted at
http://forum.java.sun.com/thread.jspa?threadID=579946
but tweaked since then), but what I really want is a
solution. I.E. I'm not sure I'm even going about this
problem in the right way, which is why I defined it
in such general terms up above. If it can/should be
done without a JList or JScrollPane, that's fine.No reason it can't.
It seems a common enough feature to want in a gui,
surely there's a common way of implementing it?There is a "proper" way, which clearly you aren't doing. :-)