Cocoa: Work around faulty screen list on startup

The NSScreen API has been observed to a return a
screen list with one mirrored, non-primary screen
when Qt is running as a startup item. Always use
the screen if there's only one screen in the list.

Change-Id: I721e25bb7595599287b97f6528e04060ce5da6c1
Task-id: QTBUG-37878
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoaintegration.mm b/src/plugins/platforms/cocoa/qcocoaintegration.mm
index fca7fa042c..9fd05a65ee 100644
--- a/src/plugins/platforms/cocoa/qcocoaintegration.mm
+++ b/src/plugins/platforms/cocoa/qcocoaintegration.mm
@@ -370,11 +370,15 @@ void QCocoaIntegration::updateScreens()
         return;
     QSet<QCocoaScreen*> remainingScreens = QSet<QCocoaScreen*>::fromList(mScreens);
     QList<QPlatformScreen *> siblings;
-    for (uint i = 0; i < [screens count]; i++) {
+    uint screenCount = [screens count];
+    for (uint i = 0; i < screenCount; i++) {
         NSScreen* scr = [screens objectAtIndex:i];
         CGDirectDisplayID dpy = [[[scr deviceDescription] objectForKey:@"NSScreenNumber"] unsignedIntValue];
         // If this screen is a mirror and is not the primary one of the mirror set, ignore it.
-        if (CGDisplayIsInMirrorSet(dpy)) {
+        // Exception: The NSScreen API has been observed to a return a screen list with one
+        // mirrored, non-primary screen when Qt is running as a startup item. Always use the
+        // screen if there's only one screen in the list.
+        if (screenCount > 1 && CGDisplayIsInMirrorSet(dpy)) {
             CGDirectDisplayID primary = CGDisplayMirrorsDisplay(dpy);
             if (primary != kCGNullDirectDisplay && primary != dpy)
                 continue;