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Groups > comp.lang.java.gui > #4698

Re: fighting over the scroller

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In article <1c0j779arr138ua3kr50ed1ju8u5jm0of3@4ax.com>,
 Roedy Green <see_website@mindprod.com.invalid> wrote:

> On Tue, 20 Sep 2011 19:15:10 -0400, "John B. Matthews"
> <nospam@nospam.invalid> wrote, quoted or indirectly quoted someone who
> said :
> 
> >This example highlights the effect. While it's easy to demonstrate 
> >contention, say by simultaneously gesturing with the mouse and 
> >holding down an arrow key, correct use of the EDT keeps events 
> >well-ordered.
> >
> ><http://stackoverflow.com/questions/7201509>
> >
> >Is this a problem in practice?
> 
> The practical problem I notice is at
> http://mindprod.com/applet/vercheck.html
> 
> Vercheck displays a scrollable table.  You can ask it to update each 
> row of the table by probing the corresponding web site in turn.  As 
> it goes it scrolls the table to keep the item it is working on in 
> view.
> 
> However, sometimes you want to override this behaviour to take a look 
> at something off screen.  You scroll, but the program immediately 
> yanks you away.  I would like it to suppress programmatic scrolling 
> for X seconds since if you scrolled, presumably you are looking at 
> something and don't want it scrolled offscreen.

I see. Text components [1] have a DefaultCaret [2], which maintains an 
UpdatePolicy property that's useful in this context. In contrast, you 
have to manage it yourself for JTable.

I typically establish a suitable attribute:

    private boolean isAutoScroll;

And scroll accordingly:

    if (isAutoScroll) {
        Rectangle r = table.getCellRect(...);
        table.scrollRectToVisible(r);
    }

One convenient approach is to condition the property in an 
AdjustmentListener:

    public void adjustmentValueChanged(AdjustmentEvent e) {
        isAutoScroll = !e.getValueIsAdjusting();
    }

This has the effect of not scrolling while the mouse is dragging the 
thumb and resuming scrolling when the mouse is released. Of course, 
other schemes are possible. A user preference wouldn't be unwarranted.

> This desired behaviour is something I think JScrollPane should always 
> do, not just in Vercheck.

I'd think it depends the content, as with text components.

[1]<http://tips4java.wordpress.com/2008/10/22/text-area-scrolling/>
[2]<http://download.oracle.com/javase/7/docs/api/javax/swing/text/DefaultCaret.html>

-- 
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>

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fighting over the scroller Roedy Green <see_website@mindprod.com.invalid> - 2011-09-20 13:51 -0700
  Re: fighting over the scroller "John B. Matthews" <nospam@nospam.invalid> - 2011-09-20 19:15 -0400
    Re: fighting over the scroller Roedy Green <see_website@mindprod.com.invalid> - 2011-09-20 23:21 -0700
      Re: fighting over the scroller "John B. Matthews" <nospam@nospam.invalid> - 2011-09-22 13:41 -0400
        Re: fighting over the scroller Roedy Green <see_website@mindprod.com.invalid> - 2011-09-22 18:34 -0700
          Re: fighting over the scroller "John B. Matthews" <nospam@nospam.invalid> - 2011-09-22 23:26 -0400

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