Check the gesturemanager pointer before accessing it.

This fixes a crash when a static QWidget is destroyed after the QApplication
object.

Task-number: QTBUG-12025
Reviewed-by: Zeno Albisser

3 files changed, 12 insertions, 9 deletions

diff --git a/src/gui/graphicsview/qgraphicsitem.cpp b/src/gui/graphicsview/qgraphicsitem.cpp
index 5fffefb..a2ae385 100644
--- a/src/gui/graphicsview/qgraphicsitem.cpp
+++ b/src/gui/graphicsview/qgraphicsitem.cpp
@@ -1453,9 +1453,10 @@ QGraphicsItem::~QGraphicsItem()
 #ifndef QT_NO_GESTURES
     if (d_ptr->isObject && !d_ptr->gestureContext.isEmpty()) {
         QGraphicsObject *o = static_cast<QGraphicsObject *>(this);
-        QGestureManager *manager = QGestureManager::instance();
-        foreach (Qt::GestureType type, d_ptr->gestureContext.keys())
-            manager->cleanupCachedGestures(o, type);
+        if (QGestureManager *manager = QGestureManager::instance()) {
+            foreach (Qt::GestureType type, d_ptr->gestureContext.keys())
+                manager->cleanupCachedGestures(o, type);
+        }
     }
 #endif
 
diff --git a/src/gui/kernel/qapplication.cpp b/src/gui/kernel/qapplication.cpp
index aaf479f..5c333b0 100644
--- a/src/gui/kernel/qapplication.cpp
+++ b/src/gui/kernel/qapplication.cpp
@@ -5791,10 +5791,12 @@ Q_GUI_EXPORT void qt_translateRawTouchEvent(QWidget *window,
 #ifndef QT_NO_GESTURES
 QGestureManager* QGestureManager::instance()
 {
-    QApplicationPrivate *qAppPriv = QApplicationPrivate::instance();
-    if (!qAppPriv->gestureManager)
-        qAppPriv->gestureManager = new QGestureManager(qApp);
-    return qAppPriv->gestureManager;
+    if (QApplicationPrivate *qAppPriv = QApplicationPrivate::instance()) {
+        if (!qAppPriv->gestureManager)
+            qAppPriv->gestureManager = new QGestureManager(qApp);
+        return qAppPriv->gestureManager;
+    }
+    return 0;
 }
 #endif // QT_NO_GESTURES
 
diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index fed8d0a..aaa29a1 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -12049,8 +12049,8 @@ void QWidget::ungrabGesture(Qt::GestureType gesture)
 {
     Q_D(QWidget);
     if (d->gestureContext.remove(gesture)) {
-        QGestureManager *manager = QGestureManager::instance();
-        manager->cleanupCachedGestures(this, gesture);
+        if (QGestureManager *manager = QGestureManager::instance())
+            manager->cleanupCachedGestures(this, gesture);
     }
 }
 #endif // QT_NO_GESTURES