QQuickScrollBarAttached: fix change listener removal

Before bb2a6c6 QQuickScrollBarAttached called

   flickable->updateOrAddGeometryChangeListener(Size)

when attaching to a Flickable, and

   flickable->removeItemChangeListener(Geometry)

when detaching from a Flickable. In bb2a6c6 the latter was changed to

   flickable->updateOrRemoveGeometryChangeListener(listener, Size)

to make the attach and detach operations nice and symmetric.

Now the problem is that updateOrRemoveGeometryChangeListener(Size)
doesn't actually remove the listener, but just resets the geometry
types it listens to. Thus, upon destruction of QQuickScrollBarAttached,
it leaves behind a dangling pointer in Flickable's list of change
listeners.

We can call either of these to fix the problem:

   flickable->updateOrRemoveGeometryChangeListener(Nothing)
   flickable->removeItemChangeListener(Geometry)

The former does essentially the latter with some extra overhead,
so we'll just revert back to how it was before bb2a6c6.

I added a warning note, also to ScrollIndicator since it's using
the same approach, to avoid the same pitfall in the future.

Change-Id: Ibdce15b22edf549491426d769b74b18daf0500ca
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

0 files changed, 0 insertions, 0 deletions