By popular demand (my own taste, and a request of a tester), I hide a button when we can
no longer scroll in this direction...
I replaced the hackish test:
if (scrollRightButton.isVisible())
with a specialized field:
private boolean isScrolling;
The following are the added / modified methods with regard to my previous
message:
private void adjustScroll(int diff)
{
int newLeft = parsePosition(tabBar.getElement().getStyle().getLeft()) +
diff;
if (newLeft <= 0)
{
int gap = computeGap();
if (gap < -newLeft)
{
// If we are about to scroll too far away from the right
border, adjust back
newLeft += -newLeft - gap;
}
}
else
{
// Don't scroll for a positive newLeft
newLeft = 0;
}
scrollTo(newLeft);
}
/**
* Gap = distance between right of last tab and right of the tab bar.
*/
private int computeGap()
{
Widget lastTab = getLastTab();
if (lastTab == null)
return 0;
return getRightPosition(lastTab) - getTabBarWidth();
}
private void showScrollButtonsIfNecessary()
{
// Defer size calculations until sizes are available.
// When calculating immediately after add(), all size methods return
zero.
Scheduler.get().scheduleDeferred(new Scheduler.ScheduledCommand()
{
@Override
public void execute()
{
boolean shouldScroll = isScrollingNecessary();
if (isScrolling)
{
if (!shouldScroll)
{
// The scroll buttons are being hidden, reset the scroll position
to zero to avoid
// having tabs starting in the middle of the window!
scrollTo(0);
}
else
{
// Resizing or adding / removing tabs, recompute the
scroll
adjustScroll(0);
}
}
else
{
// Was not scrolling, show leftmost tab and adjust scroll button
visibility
scrollTo(0);
}
}
});
}
private void scrollTo(int pos)
{
tabBar.getElement().getStyle().setLeft(pos, Unit.PX);
// Change visibility of the scroll buttons, depending on the current
scrolling
isScrolling = pos < 0;
// Visible if not in the rightmost position
scrollLeftButton.setVisible(isScrolling);
// Visible if not in the leftmost position (and if we must scroll)
scrollRightButton.setVisible(isScrollingNecessary() && computeGap() !=
-pos);
}
HTH.
--
Philippe Lhoste
-- (near) Paris -- France
-- http://Phi.Lho.free.fr
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