PointerHandlers: fix some grab notification and signal order problems

The singlePointHandlerProperties manual test showed how this was broken
in a couple of ways after 8c659c6c723e4f5f97f46a4555a4765e85c26f1d :
- When QQuickPointerTouchEvent::reset() is swapping one point instance
for another, and consequently transferring the grabbers from one to
another, it should not cause onGrabChanged to occur.  Every point
update was triggering DragHandler.onGrabChanged.
- The order of signal emission is important so that sceneGrabPos
will be correct in onGrabChanged.

Change-Id: I62a302d6e54126ae10834b6d622e82aa0e434bab
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

3 files changed, 15 insertions, 5 deletions

diff --git a/src/quick/handlers/qquickpointersinglehandler.cpp b/src/quick/handlers/qquickpointersinglehandler.cpp
index d9a9d692ae..112c680d3c 100644
--- a/src/quick/handlers/qquickpointersinglehandler.cpp
+++ b/src/quick/handlers/qquickpointersinglehandler.cpp
@@ -148,15 +148,17 @@ bool QQuickPointerSingleHandler::wantsEventPoint(QQuickEventPoint *point)
 
 void QQuickPointerSingleHandler::onGrabChanged(QQuickPointerHandler *grabber, QQuickEventPoint::GrabState stateChange, QQuickEventPoint *point)
 {
-    QQuickPointerHandler::onGrabChanged(grabber, stateChange, point);
     if (grabber != this)
         return;
     switch (stateChange) {
     case QQuickEventPoint::GrabExclusive:
+        m_sceneGrabPos = point->sceneGrabPos();
         setActive(true);
-        Q_FALLTHROUGH();
+        QQuickPointerHandler::onGrabChanged(grabber, stateChange, point);
+        break;
     case QQuickEventPoint::GrabPassive:
         m_sceneGrabPos = point->sceneGrabPos();
+        QQuickPointerHandler::onGrabChanged(grabber, stateChange, point);
         break;
     case QQuickEventPoint::OverrideGrabPassive:
         return; // don't emit
@@ -165,6 +167,7 @@ void QQuickPointerSingleHandler::onGrabChanged(QQuickPointerHandler *grabber, QQ
     case QQuickEventPoint::CancelGrabPassive:
     case QQuickEventPoint::CancelGrabExclusive:
         // the grab is lost or relinquished, so the point is no longer relevant
+        QQuickPointerHandler::onGrabChanged(grabber, stateChange, point);
         reset();
         break;
     }
diff --git a/src/quick/items/qquickevents.cpp b/src/quick/items/qquickevents.cpp
index 49ed0f050e..61d843210e 100644
--- a/src/quick/items/qquickevents.cpp
+++ b/src/quick/items/qquickevents.cpp
@@ -650,6 +650,10 @@ void QQuickEventPoint::setGrabberPointerHandler(QQuickPointerHandler *grabber, b
     if (exclusive) {
         if (grabber != m_exclusiveGrabber.data()) {
             if (grabber) {
+                // set variables before notifying the new grabber
+                m_exclusiveGrabber = QPointer<QObject>(grabber);
+                m_grabberIsHandler = true;
+                m_sceneGrabPos = m_scenePos;
                 grabber->onGrabChanged(grabber, GrabExclusive, this);
                 for (QPointer<QQuickPointerHandler> passiveGrabber : m_passiveGrabbers) {
                     if (passiveGrabber != grabber)
@@ -664,7 +668,7 @@ void QQuickEventPoint::setGrabberPointerHandler(QQuickPointerHandler *grabber, b
                 if (pointerEvent()->asPointerTouchEvent())
                     oldGrabberItem->touchUngrabEvent();
             }
-
+            // set variables after notifying the old grabber
             m_exclusiveGrabber = QPointer<QObject>(grabber);
             m_grabberIsHandler = true;
             m_sceneGrabPos = m_scenePos;
@@ -943,8 +947,9 @@ QQuickPointerEvent *QQuickPointerTouchEvent::reset(QEvent *event)
             point->setGrabberItem(nullptr);
             point->clearPassiveGrabbers();
         } else {
-            point->setExclusiveGrabber(grabbers.at(i));
-            point->setPassiveGrabbers(passiveGrabberses.at(i));
+            // Restore the grabbers without notifying (don't call onGrabChanged)
+            point->m_exclusiveGrabber = grabbers.at(i);
+            point->m_passiveGrabbers = passiveGrabberses.at(i);
         }
     }
     m_pointCount = newPointCount;
diff --git a/src/quick/items/qquickevents_p_p.h b/src/quick/items/qquickevents_p_p.h
index c4200ac550..2eebf131bc 100644
--- a/src/quick/items/qquickevents_p_p.h
+++ b/src/quick/items/qquickevents_p_p.h
@@ -370,6 +370,8 @@ private:
     QSizeF m_ellipseDiameters;
     QPointingDeviceUniqueId m_uniqueId;
 
+    friend class QQuickPointerTouchEvent;
+
     Q_DISABLE_COPY(QQuickEventTouchPoint)
 };