Fix crash-on-exit when embedding QNView

The QWindow and QCocoaWindow may be deleted
before the QNSView (which Cocoa keeps a reference
to).

Clear pointers to the Qt windows on QCocoaWindow
destruction and add null-pointer check to QNView::isOpaque.

Change-Id: I71764886c27bf1d14fb4e684c15e7c72e1c0a17c
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@theqtcompany.com>

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -446,6 +446,14 @@ QCocoaWindow::~QCocoaWindow()
                                               name:nil object:m_nsWindow];
     }
 
+    // The QNSView object may outlive the corresponding QCocoaWindow object,
+    // for example during app shutdown when the QNSView is embedded in a
+    // foregin NSView hiearchy. Clear the pointers to the QWindow/QCocoaWindow
+    // here to make sure QNSView does not dereference stale pointers.
+    if (m_qtView) {
+        [m_qtView clearQWindowPointers];
+    }
+
     foreach (QCocoaWindow *child, m_childWindows) {
        [m_nsWindow removeChildWindow:child->m_nsWindow];
         child->m_parentCocoaWindow = 0;

src/plugins/platforms/cocoa/qnsview.h

@@ -80,6 +80,7 @@ Q_FORWARD_DECLARE_OBJC_CLASS(QT_MANGLE_NAMESPACE(QNSViewMouseMoveHelper));
 
 - (id)init;
 - (id)initWithQWindow:(QWindow *)window platformWindow:(QCocoaWindow *) platformWindow;
+- (void) clearQWindowPointers;
 #ifndef QT_NO_OPENGL
 - (void)setQCocoaGLContext:(QCocoaGLContext *)context;
 #endif

src/plugins/platforms/cocoa/qnsview.mm

@@ -214,6 +214,12 @@ static NSString *_q_NSWindowDidChangeOcclusionStateNotification = nil;
     return self;
 }
 
+- (void) clearQWindowPointers
+{
+    m_window = 0;
+    m_platformWindow = 0;
+}
+
 #ifndef QT_NO_OPENGL
 - (void) setQCocoaGLContext:(QCocoaGLContext *)context
 {
@@ -481,6 +487,8 @@ QT_WARNING_POP
 
 - (BOOL) isOpaque
 {
+    if (!m_platformWindow)
+        return true;
     return m_platformWindow->isOpaque();
 }