QQuickItem: avoid emitting signals during destruction

Origin: upstream, https://code.qt.io/cgit/qt/qtdeclarative.git/commit/?id=74873324bdf33997
Last-Update: 2023-02-26

If a QQuickItem is in the QQuickItem destructor, then it is both unsafe
and unnecessary to emit property change notifications. Connected code
can no longer rely on the state of the emitting object - if it was
originally a subclass of QQuickItem, then those subclass destructors
will already have run. And the QQuickItem destructor will also have
partially run, leaving the object in an undefined state.

Add a flag that we set to true at the top of ~QQuickItem, and don't emit
visibleChildrenChanged, parentChanged, visibleChanged, and
childrenChanged for items that are partially destroyed already.

[ChangeLog][Qt Quick][QQuickItem] QQuickItem no longer emits change
notifications for the parent, children, visible, and visibleChildren
properties while it is being destroyed.

Gbp-Pq: Name qquickitem_no_signals_on_destruction.patch

diff --git a/src/quick/items/qquickitem.cpp b/src/quick/items/qquickitem.cpp
index c655b4c3276c3c19352e9427c6c1966a611aeb63..bc7dc52cac18c02afa60f5e55b8b9a18a27ef14c 100644 (file)
--- a/src/quick/items/qquickitem.cpp
+++ b/src/quick/items/qquickitem.cpp
@@ -2328,6 +2328,7 @@ QQuickItem::QQuickItem(QQuickItemPrivate &dd, QQuickItem *parent)
 QQuickItem::~QQuickItem()
 {
     Q_D(QQuickItem);
+    d->inDestructor = true;
 
     if (d->windowRefCount > 1)
         d->windowRefCount = 1; // Make sure window is set to null in next call to derefWindow().
@@ -2695,9 +2696,8 @@ void QQuickItem::setParentItem(QQuickItem *parentItem)
 
         const bool wasVisible = isVisible();
         op->removeChild(this);
-        if (wasVisible) {
+        if (wasVisible && !op->inDestructor)
             emit oldParentItem->visibleChildrenChanged();
-        }
     } else if (d->window) {
         QQuickWindowPrivate::get(d->window)->parentlessItems.remove(this);
     }
@@ -2774,8 +2774,9 @@ void QQuickItem::setParentItem(QQuickItem *parentItem)
 
     d->itemChange(ItemParentHasChanged, d->parentItem);
 
-    emit parentChanged(d->parentItem);
-    if (isVisible() && d->parentItem)
+    if (!d->inDestructor)
+        emit parentChanged(d->parentItem);
+    if (isVisible() && d->parentItem && !QQuickItemPrivate::get(d->parentItem)->inDestructor)
         emit d->parentItem->visibleChildrenChanged();
 }
 
@@ -2971,7 +2972,8 @@ void QQuickItemPrivate::removeChild(QQuickItem *child)
 
     itemChange(QQuickItem::ItemChildRemovedChange, child);
 
-    emit q->childrenChanged();
+    if (!inDestructor)
+        emit q->childrenChanged();
 }
 
 void QQuickItemPrivate::refWindow(QQuickWindow *c)
@@ -3200,6 +3202,7 @@ QQuickItemPrivate::QQuickItemPrivate()
     , touchEnabled(false)
 #endif
     , hasCursorHandler(false)
+    , inDestructor(false)
     , dirtyAttributes(0)
     , nextDirtyItem(nullptr)
     , prevDirtyItem(nullptr)
@@ -6112,9 +6115,11 @@ bool QQuickItemPrivate::setEffectiveVisibleRecur(bool newEffectiveVisible)
         QAccessible::updateAccessibility(&ev);
     }
 #endif
-    emit q->visibleChanged();
-    if (childVisibilityChanged)
-        emit q->visibleChildrenChanged();
+    if (!inDestructor) {
+        emit q->visibleChanged();
+        if (childVisibilityChanged)
+            emit q->visibleChildrenChanged();
+    }
 
     return true;    // effective visibility DID change
 }

diff --git a/src/quick/items/qquickitem_p.h b/src/quick/items/qquickitem_p.h
index d48b5510640cc3c92350ab239e8fde16cd84f59a..6f329bd119b3a0fcaefded93f472e92bf14818a9 100644 (file)
--- a/src/quick/items/qquickitem_p.h
+++ b/src/quick/items/qquickitem_p.h
@@ -472,6 +472,7 @@ public:
     bool replayingPressEvent:1;
     bool touchEnabled:1;
     bool hasCursorHandler:1;
+    quint32 inDestructor:1; // has entered ~QQuickItem
 
     enum DirtyType {
         TransformOrigin         = 0x00000001,

diff --git a/tests/auto/quick/qquickitem2/tst_qquickitem.cpp b/tests/auto/quick/qquickitem2/tst_qquickitem.cpp
index c8ef36ee6893552ce43e0f3afcf66b7190b5cc20..0b9b4ffd7108c42df7894730e0cbf698c1097548 100644 (file)
--- a/tests/auto/quick/qquickitem2/tst_qquickitem.cpp
+++ b/tests/auto/quick/qquickitem2/tst_qquickitem.cpp
@@ -132,6 +132,8 @@ private slots:
 
     void grab();
 
+    void signalsOnDestruction();
+
 private:
     QQmlEngine engine;
     bool qt_tab_all_widgets() {
@@ -3532,6 +3534,52 @@ void tst_QQuickItem::isAncestorOf()
     QVERIFY(!sub2.isAncestorOf(&sub2));
 }
 
+/*
+    Items that are getting destroyed should not emit property change notifications.
+*/
+void tst_QQuickItem::signalsOnDestruction()
+{
+    QQuickWindow window;
+    window.show();
+
+    // visual children, but not QObject children
+    std::unique_ptr<QQuickItem> parent(new QQuickItem(window.contentItem()));
+    std::unique_ptr<QQuickItem> child(new QQuickItem);
+    std::unique_ptr<QQuickItem> grandChild(new QQuickItem);
+
+    QSignalSpy childrenSpy(parent.get(), &QQuickItem::childrenChanged);
+    QSignalSpy visibleChildrenSpy(parent.get(), &QQuickItem::visibleChildrenChanged);
+    QSignalSpy childParentSpy(child.get(), &QQuickItem::parentChanged);
+    QSignalSpy childChildrenSpy(child.get(), &QQuickItem::childrenChanged);
+    QSignalSpy childVisibleChildrenSpy(child.get(), &QQuickItem::visibleChanged);
+    QSignalSpy grandChildParentSpy(grandChild.get(), &QQuickItem::parentChanged);
+
+    child->setParentItem(parent.get());
+    QCOMPARE(childrenSpy.count(), 1);
+    QCOMPARE(visibleChildrenSpy.count(), 1);
+    QCOMPARE(childParentSpy.count(), 1);
+    QCOMPARE(childChildrenSpy.count(), 0);
+    QCOMPARE(childVisibleChildrenSpy.count(), 0);
+
+    grandChild->setParentItem(child.get());
+    QCOMPARE(childrenSpy.count(), 1);
+    QCOMPARE(visibleChildrenSpy.count(), 1);
+    QCOMPARE(childParentSpy.count(), 1);
+    QCOMPARE(childChildrenSpy.count(), 1);
+    QCOMPARE(childVisibleChildrenSpy.count(), 0);
+    QCOMPARE(grandChildParentSpy.count(), 1);
+
+    parent.reset();
+
+    QVERIFY(!child->parentItem());
+    QVERIFY(grandChild->parentItem());
+    QCOMPARE(childrenSpy.count(), 1);
+    QCOMPARE(visibleChildrenSpy.count(), 1);
+    QCOMPARE(childParentSpy.count(), 2);
+    QCOMPARE(grandChildParentSpy.count(), 1);
+}
+
+
 QTEST_MAIN(tst_QQuickItem)
 
 #include "tst_qquickitem.moc"