unify handler grab state handling into onGrabChanged

onGrabChanged and handleGrab looked redundant.  It was also not clear
how important it is for handlers to react to passive ungrabs, overrides
or cancellations.  Rather than debating about when to call one of these
and when not to, let's centralize the responsibility in
QQuickEventPoint (because the grabber pointers are stored there, so
it's the ultimate destination of any grab change), and let's notify
all the relevant handlers about all changes, with enough information
that each handler can decide for itself what's important and what
isn't.  But so far most handlers don't need to override this virtual.
The base class QQuickPointerHandler takes care of setting the
active property to false, rejecting the eventpoint, and unsetting
keepMouseGrab and keepTouchGrab whenever grab is lost; and emitting
grabChanged or canceled as appropriate to notify any QML code which
needs to know.  Subclasses mainly care about the change of active state:
they must initiate active state themselves, and may react when it
reverts to false.

Change-Id: I6c7f29472d12564d74ae091b0c81fa08fe131ce7
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 11 insertions, 7 deletions

diff --git a/src/quick/handlers/qquicktaphandler.cpp b/src/quick/handlers/qquicktaphandler.cpp
index 228b6bbaf3..b05d32f4b4 100644
--- a/src/quick/handlers/qquicktaphandler.cpp
+++ b/src/quick/handlers/qquicktaphandler.cpp
@@ -132,9 +132,9 @@ bool QQuickTapHandler::wantsEventPoint(QQuickEventPoint *point)
         }
         break;
     }
-    // If this is the grabber, returning false from this function will
-    // cancel the grab, so handleGrabCancel() and setPressed(false) will be called.
-    // But when m_gesturePolicy is DragThreshold, we don't grab, but
+    // If this is the grabber, returning false from this function will cancel the grab,
+    // so onGrabChanged(this, CancelGrabExclusive, point) and setPressed(false) will be called.
+    // But when m_gesturePolicy is DragThreshold, we don't get an exclusive grab, but
     // we still don't want to be pressed anymore.
     if (!ret)
         setPressed(false, true, point);
@@ -254,7 +254,10 @@ void QQuickTapHandler::setPressed(bool press, bool cancel, QQuickEventPoint *poi
             m_longPressTimer.stop();
             m_holdTimer.invalidate();
         }
-        setPassiveGrab(point, press);
+        if (m_gesturePolicy == DragThreshold)
+            setPassiveGrab(point, press);
+        else
+            setExclusiveGrab(point, press);
         if (!cancel && !press && point->timeHeld() < longPressThreshold()) {
             // Assuming here that pointerEvent()->timestamp() is in ms.
             qreal ts = point->pointerEvent()->timestamp() / 1000.0;
@@ -274,10 +277,11 @@ void QQuickTapHandler::setPressed(bool press, bool cancel, QQuickEventPoint *poi
     }
 }
 
-void QQuickTapHandler::handleGrabCancel(QQuickEventPoint *point)
+void QQuickTapHandler::onGrabChanged(QQuickPointerHandler *grabber, QQuickEventPoint::GrabState stateChange, QQuickEventPoint *point)
 {
-    QQuickPointerSingleHandler::handleGrabCancel(point);
-    setPressed(false, true, point);
+    QQuickPointerSingleHandler::onGrabChanged(grabber, stateChange, point);
+    if (grabber == this && stateChange == QQuickEventPoint::CancelGrabExclusive)
+        setPressed(false, true, point);
 }
 
 void QQuickTapHandler::connectPreRenderSignal(bool conn)