Fix interaction of QQuickItems with the garbage collector

The QObject ownership of QQuickItem objects is not accessible / mutable
in QML, because the parent property maps to the (dynamic) visual parent.

There are use-cases of creating QQuickItem objects without a QObject parent and
to support this, the visual parent needs to mark its visual children in order
to provide intuitive semantics.

[ChangeLog][QtQuick][Import Behavior Changes] A QQuick Item is now strongly
referenced by its visual parent item, so it doesn't require a QObject parent to
stay alive.

Task-number: QTBUG-35913
Change-Id: Ief2d40ac76298a0cf241ca73ff654c4ecfa12748
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/src/quick/items/qquickview_p.h b/src/quick/items/qquickview_p.h
index 170c93a6cf..e18b45dfbe 100644
--- a/src/quick/items/qquickview_p.h
+++ b/src/quick/items/qquickview_p.h
@@ -51,12 +51,17 @@
 #include <QtCore/QWeakPointer>
 
 #include <QtQml/qqmlengine.h>
+#include <private/qv4object_p.h>
 #include "qquickwindow_p.h"
 
 #include "qquickitemchangelistener_p.h"
 
 QT_BEGIN_NAMESPACE
 
+namespace QV4 {
+struct ExecutionEngine;
+}
+
 class QQmlContext;
 class QQmlError;
 class QQuickItem;
@@ -94,6 +99,23 @@ public:
     QQuickView::ResizeMode resizeMode;
     QSize initialSize;
     QElapsedTimer frameTimer;
+    QV4::PersistentValue rootItemMarker;
+};
+
+struct QQuickRootItemMarker : public QV4::Object
+{
+    Q_MANAGED
+
+    QQuickRootItemMarker(QQuickViewPrivate *view);
+
+    static void destroy(Managed *that)
+    {
+        static_cast<QQuickRootItemMarker*>(that)->~QQuickRootItemMarker();
+    }
+
+    static void markObjects(Managed *that, QV4::ExecutionEngine *e);
+
+    QQuickViewPrivate *view;
 };
 
 QT_END_NAMESPACE