Avoid needless notifications when destroying layouts

When deleting a layout with children, it ends up in ~QQuickItem(), which in
turn will call setParentItem(0).  setParentItem(0) will in turn call
setEffectiveVisibleRecur(), which will recurse down all its descendants.
Therefore, deleting a top level layout might trigger item change listeners
for *all* its descendants, not only its direct children.

This behavior might even cause crashes: The visibility changes will then
trigger an invalidation of the layout, which will propagate up the parent
hierarchy, and potentially call invalidate() on a partially-destroyed
layout, which then might crash.

Change-Id: I48e11d57f69e9011ced6c3a0b51e3d89b24ad5c1
Task-number: QTBUG-55103
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/imports/layouts/qquicklayout_p.h b/src/imports/layouts/qquicklayout_p.h
index eece6f8658..113498eb2b 100644
--- a/src/imports/layouts/qquicklayout_p.h
+++ b/src/imports/layouts/qquicklayout_p.h
@@ -95,6 +95,7 @@ public:
     void itemChange(ItemChange change, const ItemChangeData &value) Q_DECL_OVERRIDE;
     void geometryChanged(const QRectF &newGeometry, const QRectF &oldGeometry)  Q_DECL_OVERRIDE;
     bool isReady() const;
+    void deactivateRecur();
 
 
     /* QQuickItemChangeListener */
@@ -134,6 +135,7 @@ public:
 protected:
     unsigned m_isReady : 1;
     unsigned m_disableRearrange : 1;
+    unsigned m_hasItemChangeListeners : 1;      // if false, we don't need to remove its item change listeners...
     mutable QSet<QQuickItem *> m_ignoredItems;
 };