>From qt4-doc about `QWidget::setContentsMargins':
"Changing the margins will trigger a resizeEvent()."
and within src/gui/kernel/qwidget.cpp (qt-4.8.6):
if (left == d->leftmargin && top == d->topmargin
&& right == d->rightmargin && bottom == d->bottommargin)
return;
...
so resizeEvent() is called only if the margins are changed.
It means that the current order in `RosegardenScrollView::resizeEvent' is:
QAbstractScrollArea::resizeEvent
RosegardenScrollView::updateScrollBars
QWidget::setContentsMargins (from updateBottomWidgetGeometry)
+---> QAbstractScrollArea::resizeEvent if the margins are changed
and we can get a loop
+---> resizeEvent ---> setContentsMargins---+
| |
| v
+-------------------<-----------------------+
i.e. when the horizontal scrollbar appairs and the value for
verticalScrollBar()->setMaximum(
std::max(contentsHeight() - visibleHeight(), 0));
in `updateScrollBars' jumps from 0 to a little positive value.
On Sun, Apr 26, 2015 at 09:38:09PM -0400, Ted Felix wrote:
> It's probably the enormous number of resize events that are sent out
> with the animated resizing. I see hundreds of them, then the endless
> loop and crash.
Here is the loop:
0) resizeEvent
1) verticalScrollBar()->setMaximum(nonzero);
2) setContentsMargins
3) margins changed -> resizeEvent
4) verticalScrollBar()->setMaximum(0);
5) setContentsMargin
6) margins changed -> resizeEvent
7) goto 1
However, after the swap between `updateBottomWidgetGeometry' and
`updateScrollBars', proposed in
http://sourceforge.net/p/rosegarden/mailman/message/34048181/
the order becomes:
QAbstractScrollArea::resizeEvent
QWidget::setContentsMargins
+---> QAbstractScrollArea::resizeEvent if the margins are changed
RosegardenScrollView::updateScrollBars();
Now the loop 'setContentsMargins @ resizeEvent' stops after the first step:
resizeEvent
setContentsMargins
margins changed -> resizeEvent
setContentsMargins
margins changed -> NO
It makes sense, so the bug is fixed.
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