Don't crash when QTouchEvent is accepted but not handled by a

QGraphicsItem

After propagating QEvent::TouchBegin, if there is no item that has
accepted and handled the event, we must remove the touch point from our
data structures.

In this situation, QGraphicsScene will ignore the TouchBegin, as will
QGraphicsView, and QApplication will respond by not sending any more
touch events to the view/scene/item. This means our logic for handling
TouchPointReleased points will never be called (and the QGraphicsScene's
itemForTouchPointId and sceneCurrentTouchPoints state will be
incorrect).

Reviewed-by: Denis Dzyubenko
Reviewed-by: Marius Storm-Olsen

2 files changed, 39 insertions, 1 deletions

diff --git a/src/gui/graphicsview/qgraphicsscene.cpp b/src/gui/graphicsview/qgraphicsscene.cpp
index 86aaa78..4472272 100644
--- a/src/gui/graphicsview/qgraphicsscene.cpp
+++ b/src/gui/graphicsview/qgraphicsscene.cpp
@@ -5712,8 +5712,15 @@ void QGraphicsScenePrivate::touchEventHandler(QTouchEvent *sceneTouchEvent)
             item->d_ptr->acceptedTouchBeginEvent = true;
             bool res = sendTouchBeginEvent(item, &touchEvent)
                        && touchEvent.isAccepted();
-            if (!res)
+            if (!res) {
+                // forget about these touch points, we didn't handle them
+                for (int i = 0; i < touchEvent.touchPoints().count(); ++i) {
+                    const QTouchEvent::TouchPoint &touchPoint = touchEvent.touchPoints().at(i);
+                    itemForTouchPointId.remove(touchPoint.id());
+                    sceneCurrentTouchPoints.remove(touchPoint.id());
+                }
                 ignoreSceneTouchEvent = false;
+            }
             break;
         }
         default:
diff --git a/tests/auto/qtouchevent/tst_qtouchevent.cpp b/tests/auto/qtouchevent/tst_qtouchevent.cpp
index 639f8e4..bb80fde 100644
--- a/tests/auto/qtouchevent/tst_qtouchevent.cpp
+++ b/tests/auto/qtouchevent/tst_qtouchevent.cpp
@@ -193,6 +193,7 @@ private slots:
     void multiPointRawEventTranslationOnTouchPad();
     void deleteInEventHandler();
     void deleteInRawEventTranslation();
+    void crashInQGraphicsSceneAfterNotHandlingTouchBegin();
 };
 
 void tst_QTouchEvent::touchDisabledByDefault()
@@ -1303,6 +1304,36 @@ void tst_QTouchEvent::deleteInRawEventTranslation()
     qt_translateRawTouchEvent(&touchWidget, QTouchEvent::TouchScreen, rawTouchPoints);
 }
 
+void tst_QTouchEvent::crashInQGraphicsSceneAfterNotHandlingTouchBegin()
+{
+    QGraphicsRectItem *rect = new QGraphicsRectItem(0, 0, 100, 100);
+    rect->setAcceptTouchEvents(true);
+
+    QGraphicsRectItem *mainRect = new QGraphicsRectItem(0, 0, 100, 100, rect);
+    mainRect->setBrush(Qt::lightGray);
+
+    QGraphicsRectItem *button = new QGraphicsRectItem(-20, -20, 40, 40, mainRect);
+    button->setPos(50, 50);
+    button->setBrush(Qt::darkGreen);
+
+    QGraphicsView view;
+    QGraphicsScene scene;
+    scene.addItem(rect);
+    scene.setSceneRect(0,0,100,100);
+    view.setScene(&scene);
+
+    view.show();
+    QTest::qWaitForWindowShown(&view);
+
+    QPoint centerPos = view.mapFromScene(rect->boundingRect().center());
+    // Touch the button
+    QTest::touchEvent(view.viewport()).press(0, centerPos);
+    QTest::touchEvent(view.viewport()).release(0, centerPos);
+    // Touch outside of the button
+    QTest::touchEvent(view.viewport()).press(0, view.mapFromScene(QPoint(10, 10)));
+    QTest::touchEvent(view.viewport()).release(0, view.mapFromScene(QPoint(10, 10)));
+}
+
 QTEST_MAIN(tst_QTouchEvent)
 
 #include "tst_qtouchevent.moc"