Cocoa: NSMenu views never get viewDidUnhide called

This is the case for QWidgets added as native menu items with
QWidgetAction. According to Cocoa's documentation [1], we should
rely on -[QNSView viewDidMoveToWindow] instead.

On 10.9 however, we receive NSWindowDidChangeOcclusionStateNotification
from the NSMenu window, which is preferable to using -[QNSView
viewDidMoveToWindow] as it guarantees the view is actually visible.
We do runtime symbol lookup to get this to work on 10.9 regardless
of the build SDK version.

[1] https://developer.apple.com/library/mac/documentation/cocoa/Conceptual/MenuList/Articles/ViewsInMenuItems.html

Task-number: QTBUG-19840
Change-Id: If4676df5d79c359965f09ef2e5eddf4c925e3533
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

src/plugins/platforms/cocoa/qnsview.mm

@@ -42,6 +42,7 @@
 #include <QtCore/qglobal.h>
 
 #include <Carbon/Carbon.h>
+#include <dlfcn.h>
 
 #include "qnsview.h"
 #include "qcocoawindow.h"
@@ -65,6 +66,9 @@
 
 static QTouchDevice *touchDevice = 0;
 
+// ### HACK Remove once 10.8 is unsupported
+static NSString *_q_NSWindowDidChangeOcclusionStateNotification = nil;
+
 @interface NSEvent (Qt_Compile_Leopard_DeviceDelta)
   - (CGFloat)deviceDeltaX;
   - (CGFloat)deviceDeltaY;
@@ -73,6 +77,13 @@ static QTouchDevice *touchDevice = 0;
 
 @implementation QNSView
 
++ (void)initialize
+{
+    NSString **notificationNameVar = (NSString **)dlsym(RTLD_NEXT, "NSWindowDidChangeOcclusionStateNotification");
+    if (notificationNameVar)
+        _q_NSWindowDidChangeOcclusionStateNotification = *notificationNameVar;
+}
+
 - (id) init
 {
     self = [super initWithFrame : NSMakeRect(0,0, 300,300)];
@@ -192,6 +203,19 @@ static QTouchDevice *touchDevice = 0;
     }
 }
 
+- (void)viewDidMoveToWindow
+{
+    if (self.window) {
+        // This is the case of QWidgetAction's generated QWidget inserted in an NSMenu.
+        // 10.9 and newer get the NSWindowDidChangeOcclusionStateNotification
+        if (!_q_NSWindowDidChangeOcclusionStateNotification
+            && [self.window.className isEqualToString:@"NSCarbonMenuWindow"])
+            m_platformWindow->exposeWindow();
+    } else {
+        m_platformWindow->obscureWindow();
+    }
+}
+
 - (void)viewWillMoveToWindow:(NSWindow *)newWindow
 {
     // ### Merge "normal" window code path with this one for 5.1.
@@ -325,6 +349,23 @@ static QTouchDevice *touchDevice = 0;
         m_platformWindow->obscureWindow();
     } else if ([notificationName isEqualToString: @"NSWindowDidOrderOnScreenAndFinishAnimatingNotification"]) {
         m_platformWindow->exposeWindow();
+    } else if (_q_NSWindowDidChangeOcclusionStateNotification
+               && [notificationName isEqualToString:_q_NSWindowDidChangeOcclusionStateNotification]) {
+#if MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_9
+// ### HACK Remove the enum declaration, the warning disabling and the cast further down once 10.8 is unsupported
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wobjc-method-access"
+        enum { NSWindowOcclusionStateVisible = 1UL << 1 };
+#endif
+        // Older versions managed in -[QNSView viewDidMoveToWindow].
+        // Support QWidgetAction in NSMenu. Mavericks only sends this notification.
+        // Ideally we should support this in Qt as well, in order to disable animations
+        // when the window is occluded.
+        if ((NSUInteger)[self.window occlusionState] & NSWindowOcclusionStateVisible)
+            m_platformWindow->exposeWindow();
+#if MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_9
+#pragma clang diagnostic pop
+#endif
     } else if (notificationName == NSWindowDidChangeScreenNotification) {
         if (m_window) {
             NSUInteger screenIndex = [[NSScreen screens] indexOfObject:self.window.screen];