Prevent stale QWidget pointers in QCocoaView

QCocoaView has two "back" pointers ot its owning QWidget
and the corresponding QWidgetPrivate. The lifetime of the
QCocoaView might be longer and that of the QWidget if Cocoa
itself holds references to it. In addition accessing a
QWidget that is being destroyed is not safe.

Set both pack pointers to NULL in ~QWidget. This prevents
following stale pointers in the QCocoaView callbacks. This
also means that we'll see the NULL pointers, add gurads for
that.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index d433048..1e9b1d9 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -1468,6 +1468,15 @@ QWidget::~QWidget()
         d->declarativeData = 0;                 // don't activate again in ~QObject
     }
 
+#ifdef QT_MAC_USE_COCOA
+    // QCocoaView holds a pointer back to this widget. Clear it now
+    // to make sure it's not followed later on. The lifetime of the
+    // QCocoaView might exceed the lifetime of this widget in cases
+    // where Cocoa itself holds references to it.
+    extern void qt_mac_clearCocoaViewQWidgetPointers(QWidget *);
+    qt_mac_clearCocoaViewQWidgetPointers(this);
+#endif
+
     if (!d->children.isEmpty())
         d->deleteChildren();