QCocoaDrag: reset the stored NSView when it gets destroyed

QCocoaDrag stores the last NSView that received an input event, which
becomes a dangling pointer when the NSView gets destroyed. Inform the
QCocoaDrag when NSView's destructor runs, so that it can reset the
pointer (and reset the NSEvent pointer as well) when the destroyed
NSView is the stored one.

With this change alone we'd end up triggering the Q_ASSERT later on in
QCocoaDrag::drag, as m_lastEvent is now nil so the NSWindow will be nil
as well. QCocoaDrag::drag cannot do anything useful if m_lastEvent is
nil, so exit early.

Pick-to: 6.8 6.5
Fixes: QTBUG-116554
Change-Id: I5949d728d05adcf3d4a32c91f7e181393bef0422
Reviewed-by: Tor Arne Vestbø <[email protected]>

3 files changed, 19 insertions, 1 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoadrag.h b/src/plugins/platforms/cocoa/qcocoadrag.h
index f470fa39a9f..30456a91bba 100644
--- a/src/plugins/platforms/cocoa/qcocoadrag.h
+++ b/src/plugins/platforms/cocoa/qcocoadrag.h
@@ -36,6 +36,7 @@ public:
     * event and view when handling an event in QNSView
     */
     void setLastInputEvent(NSEvent *event, NSView *view);
+    void viewDestroyed(NSView *view);
 
     void setAcceptedAction(Qt::DropAction act);
     void exitDragLoop();
diff --git a/src/plugins/platforms/cocoa/qcocoadrag.mm b/src/plugins/platforms/cocoa/qcocoadrag.mm
index 3b736db39b3..bbc75bf6dbe 100644
--- a/src/plugins/platforms/cocoa/qcocoadrag.mm
+++ b/src/plugins/platforms/cocoa/qcocoadrag.mm
@@ -38,6 +38,17 @@ void QCocoaDrag::setLastInputEvent(NSEvent *event, NSView *view)
     m_lastView = view;
 }
 
+void QCocoaDrag::viewDestroyed(NSView *view)
+{
+    if (view == m_lastView) {
+        if (m_lastEvent.window.contentView == view) {
+            [m_lastEvent release];
+            m_lastEvent = nil;
+        }
+        m_lastView = nil;
+    }
+}
+
 QMimeData *QCocoaDrag::dragMimeData()
 {
     if (m_drag)
@@ -95,9 +106,11 @@ Qt::DropAction QCocoaDrag::defaultAction(Qt::DropActions possibleActions,
 
 Qt::DropAction QCocoaDrag::drag(QDrag *o)
 {
-    m_drag = o;
     m_executed_drop_action = Qt::IgnoreAction;
+    if (!m_lastEvent)
+        return m_executed_drop_action;
 
+    m_drag = o;
     QMacPasteboard dragBoard(CFStringRef(NSPasteboardNameDrag), QUtiMimeConverter::HandlerScopeFlag::DnD);
     m_drag->mimeData()->setData("application/x-qt-mime-type-name"_L1, QByteArray("dummy"));
     dragBoard.setMimeData(m_drag->mimeData(), QMacPasteboard::LazyRequest);
diff --git a/src/plugins/platforms/cocoa/qnsview.mm b/src/plugins/platforms/cocoa/qnsview.mm
index 560cada5fb4..e961021d240 100644
--- a/src/plugins/platforms/cocoa/qnsview.mm
+++ b/src/plugins/platforms/cocoa/qnsview.mm
@@ -173,6 +173,10 @@ QT_NAMESPACE_ALIAS_OBJC_CLASS(QNSViewMenuHelper);
     [[NSNotificationCenter defaultCenter] removeObserver:self];
     [m_mouseMoveHelper release];
 
+    // FIXME: Replace with __weak or someting equivalent
+    QCocoaDrag* nativeDrag = QCocoaIntegration::instance()->drag();
+    nativeDrag->viewDestroyed(self);
+
     [super dealloc];
 }