QQuickHoverHandler: listen for parent changes, and update hasHoverInChild

A QQuickHoverHandler is normally created by the QML engine, but
can sometimes also be created directly from C++. And for
the latter case, QQuickHoverHandler::componentComplete() will
not be called. This causes a problem, since it takes care of
subscribing for hover events on the parent item.

To support creating hover handlers from c++, we therefore need
to also subscribe to hover events from the constructor.
Moreover, since the parentItem can change at runtime, we also
need a virtual function that informs it when the parent item
changes, so that we can remove hover subscription from the old
parent, and subscribe for it on the new parent.

Pick-to: 6.4
Change-Id: I52f3cd16d6bbfbbe2e4c3c019efdc7f06c5f2c31
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/quick/handlers/qquickhoverhandler.cpp

@@ -42,35 +42,58 @@ class QQuickHoverHandlerPrivate : public QQuickSinglePointHandlerPrivate
 
 public:
     void onEnabledChanged() override;
+    void onParentChanged(QQuickItem *oldParent, QQuickItem *newParent) override;
+
+    void updateHasHoverInChild(QQuickItem *item, bool hasHover);
 };
 
 void QQuickHoverHandlerPrivate::onEnabledChanged()
 {
     Q_Q(QQuickHoverHandler);
 
-    if (auto parent = q->parentItem()) {
-        QQuickItemPrivate *itemPriv = QQuickItemPrivate::get(parent);
-        itemPriv->setHasHoverInChild(enabled);
-        // The DA needs to resolve which items and handlers should now be hovered or unhovered.
-        // Marking the parent item dirty ensures that flushFrameSynchronousEvents() will be called from the render loop,
-        // even if this change is not in response to a mouse event and no item has already marked itself dirty.
-        itemPriv->dirty(QQuickItemPrivate::Content);
-    }
+    if (auto parent = q->parentItem())
+        updateHasHoverInChild(parent, enabled);
     if (!enabled)
         q->setHovered(false);
+
+    QQuickSinglePointHandlerPrivate::onEnabledChanged();
+}
+
+void QQuickHoverHandlerPrivate::onParentChanged(QQuickItem *oldParent, QQuickItem *newParent)
+{
+    if (oldParent)
+        updateHasHoverInChild(oldParent, false);
+    if (newParent)
+        updateHasHoverInChild(newParent, true);
+
+    QQuickSinglePointHandlerPrivate::onParentChanged(oldParent, newParent);
+}
+
+void QQuickHoverHandlerPrivate::updateHasHoverInChild(QQuickItem *item, bool hasHover)
+{
+    QQuickItemPrivate *itemPriv = QQuickItemPrivate::get(item);
+    itemPriv->setHasHoverInChild(hasHover);
+    // The DA needs to resolve which items and handlers should now be hovered or unhovered.
+    // Marking the parent item dirty ensures that flushFrameSynchronousEvents() will be called from the render loop,
+    // even if this change is not in response to a mouse event and no item has already marked itself dirty.
+    itemPriv->dirty(QQuickItemPrivate::Content);
 }
 
 QQuickHoverHandler::QQuickHoverHandler(QQuickItem *parent)
     : QQuickSinglePointHandler(*(new QQuickHoverHandlerPrivate), parent)
 {
+    Q_D(QQuickHoverHandler);
     // Tell QQuickPointerDeviceHandler::wantsPointerEvent() to ignore button state
-    d_func()->acceptedButtons = Qt::NoButton;
+    d->acceptedButtons = Qt::NoButton;
+    if (parent)
+        d->updateHasHoverInChild(parent, true);
 }
 
 QQuickHoverHandler::~QQuickHoverHandler()
 {
+    Q_D(QQuickHoverHandler);
     if (auto parent = parentItem())
-        QQuickItemPrivate::get(parent)->setHasHoverInChild(false);
+        d->updateHasHoverInChild(parent, false);
 }
 
 /*!
@@ -107,9 +130,13 @@ bool QQuickHoverHandler::event(QEvent *event)
 
 void QQuickHoverHandler::componentComplete()
 {
+    Q_D(QQuickHoverHandler);
     QQuickSinglePointHandler::componentComplete();
-    if (auto par = parentItem())
-        QQuickItemPrivate::get(par)->setHasHoverInChild(true);
+
+    if (d->enabled) {
+        if (auto parent = parentItem())
+            d->updateHasHoverInChild(parent, true);
+    }
 }
 
 bool QQuickHoverHandler::wantsPointerEvent(QPointerEvent *event)

src/quick/handlers/qquickpointerhandler.cpp

@@ -597,15 +597,18 @@ QQuickItem *QQuickPointerHandler::parentItem() const
 
 void QQuickPointerHandler::setParentItem(QQuickItem *p)
 {
+    Q_D(QQuickPointerHandler);
     if (QObject::parent() == p)
         return;
 
     qCDebug(lcHandlerParent) << "reparenting handler" << this << ":" << parent() << "->" << p;
-    if (auto *oldParent = static_cast<QQuickItem *>(QObject::parent()))
+    auto *oldParent = static_cast<QQuickItem *>(QObject::parent());
+    if (oldParent)
         QQuickItemPrivate::get(oldParent)->removePointerHandler(this);
     setParent(p);
     if (p)
         QQuickItemPrivate::get(p)->addPointerHandler(this);
+    d->onParentChanged(oldParent, p);
     emit parentChanged();
 }
 

src/quick/handlers/qquickpointerhandler_p_p.h

@@ -39,6 +39,7 @@ public:
     bool dragOverThreshold(QVector2D delta) const;
     bool dragOverThreshold(const QEventPoint &point) const;
 
+    virtual void onParentChanged(QQuickItem * /*oldParent*/, QQuickItem * /*newParent*/) {}
     virtual void onEnabledChanged() {}
 
     static QVector<QObject *> &deviceDeliveryTargets(const QInputDevice *device);

tests/auto/quick/pointerhandlers/qquickhoverhandler/data/nohandler.qml

@@ -0,0 +1,15 @@
+import QtQuick 2.15
+import QtQuick.Window 2.15
+
+Window {
+    width: 320
+    height: 240
+    visible: true
+
+    Rectangle {
+        objectName: "childItem"
+        width: 100
+        height: 100
+        color: "lightblue"
+    }
+}

tests/auto/quick/pointerhandlers/qquickhoverhandler/tst_qquickhoverhandler.cpp

@@ -46,6 +46,7 @@ private slots:
     void window();
     void deviceCursor_data();
     void deviceCursor();
+    void addHandlerFromCpp();
 
 private:
     void createView(QScopedPointer<QQuickView> &window, const char *fileName);
@@ -567,6 +568,69 @@ void tst_HoverHandler::deviceCursor()
     QCOMPARE(airbrushEraserHandler->isHovered(), true); // there was no fresh QTabletEvent to tell it not to be hovered
 }
 
+void tst_HoverHandler::addHandlerFromCpp()
+{
+    // Check that you can create a hover handler from c++, and add it
+    // as a child of an existing item. Continue to check that you can
+    // also change the parent item at runtime.
+    QQmlEngine engine;
+    QQmlComponent component(&engine);
+    component.loadUrl(testFileUrl("nohandler.qml"));
+    QScopedPointer<QQuickWindow> window(qobject_cast<QQuickWindow *>(component.create()));
+    QVERIFY(!window.isNull());
+    window->show();
+    QVERIFY(QTest::qWaitForWindowExposed(window.data()));
+
+    QQuickItem *childItem = window->findChild<QQuickItem *>("childItem");
+    QVERIFY(childItem);
+
+    // Move mouse outside child
+    const QPoint outside(200, 200);
+    const QPoint inside(50, 50);
+    QTest::mouseMove(window.data(), outside);
+
+    QQuickHoverHandler *handler = new QQuickHoverHandler(childItem);
+    QSignalSpy spy(handler, &QQuickHoverHandler::hoveredChanged);
+
+    // Move mouse inside child
+    QTest::mouseMove(window.data(), inside);
+    QVERIFY(handler->isHovered());
+    QCOMPARE(spy.count(), 1);
+
+    // Move mouse outside child
+    QTest::mouseMove(window.data(), outside);
+    QVERIFY(!handler->isHovered());
+    QCOMPARE(spy.count(), 2);
+
+    // Remove the parent item from the handler
+    spy.clear();
+    handler->setParentItem(nullptr);
+
+    // Move mouse inside child
+    QTest::mouseMove(window.data(), inside);
+    QVERIFY(!handler->isHovered());
+    QCOMPARE(spy.count(), 0);
+
+    // Move mouse outside child
+    QTest::mouseMove(window.data(), outside);
+    QVERIFY(!handler->isHovered());
+    QCOMPARE(spy.count(), 0);
+
+    // Reparent back the item to the handler
+    spy.clear();
+    handler->setParentItem(childItem);
+
+    // Move mouse inside child
+    QTest::mouseMove(window.data(), inside);
+    QVERIFY(handler->isHovered());
+    QCOMPARE(spy.count(), 1);
+
+    // Move mouse outside child
+    QTest::mouseMove(window.data(), outside);
+    QVERIFY(!handler->isHovered());
+    QCOMPARE(spy.count(), 2);
+}
+
 QTEST_MAIN(tst_HoverHandler)
 
 #include "tst_qquickhoverhandler.moc"