iOS: Decouple UIWindow management from QIOSScreen

We now adopt the UIScene lifecycle, where we react to iOS creating
UIWindowScenes for connected screens, which we then configure with
a single instance of our QUIWindow, that in turn contains the
QIOSViewController and QIOSDesktopManagerView that we depend on
for our window management.

As a result, we can now create and show QWindows on visionOS,
which doesn't have UIScreen and hence failed with our old strategy
managing our UIWindow via UISScreen.

We still do not declare a UIApplicationSceneManifest in our Info.plist,
or report UIApplicationSupportsMultipleScenes, as this adds another
level to the window management that we're not ready for yet.

Task-number: QTBUG-121781
Change-Id: Ic02f43aa6b205289a3f3c8e72c2a6ef575031d9a
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 22 insertions, 15 deletions

diff --git a/src/plugins/platforms/ios/qiosviewcontroller.mm b/src/plugins/platforms/ios/qiosviewcontroller.mm
index 4f0c8a2ecc..436d1e7bed 100644
--- a/src/plugins/platforms/ios/qiosviewcontroller.mm
+++ b/src/plugins/platforms/ios/qiosviewcontroller.mm
@@ -26,6 +26,7 @@
 // -------------------------------------------------------------------------
 
 @interface QIOSViewController ()
+@property (nonatomic, assign) UIWindow *window;
 @property (nonatomic, assign) QPointer<QT_PREPEND_NAMESPACE(QIOSScreen)> platformScreen;
 @property (nonatomic, assign) BOOL changingOrientation;
 @end
@@ -88,28 +89,25 @@
 
 - (void)didAddSubview:(UIView *)subview
 {
-#if !defined(Q_OS_VISIONOS)
     Q_UNUSED(subview);
 
-    QT_PREPEND_NAMESPACE(QIOSScreen) *screen = self.qtViewController.platformScreen;
-
-    // The 'window' property of our view is not valid until the window
-    // has been shown, so we have to access it through the QIOSScreen.
-    UIWindow *uiWindow = screen->uiWindow();
+    // Track UIWindow via explicit property on QIOSViewController,
+    // as the window property of our own view is not valid until
+    // the window has been shown (below).
+    UIWindow *uiWindow = self.qtViewController.window;
 
     if (uiWindow.hidden) {
-        // Associate UIWindow to screen and show it the first time a QWindow
-        // is mapped to the screen. For external screens this means disabling
-        // mirroring mode and presenting alternate content on the screen.
-        uiWindow.screen = screen->uiScreen();
+        // Show the UIWindow the first time a QWindow is mapped to the screen.
+        // For the main screen this hides the launch screen, while for external
+        // screens this disables mirroring of the main screen, so the external
+        // screen can be used for alternate content.
         uiWindow.hidden = NO;
     }
-#endif
 }
 
+#if !defined(Q_OS_VISIONOS)
 - (void)willRemoveSubview:(UIView *)subview
 {
-#if !defined(Q_OS_VISIONOS)
     Q_UNUSED(subview);
 
     UIWindow *uiWindow = self.window;
@@ -124,11 +122,10 @@
         // to ensure that we don't try to layout the view that's being removed.
         dispatch_async(dispatch_get_main_queue(), ^{
             uiWindow.hidden = YES;
-            uiWindow.screen = [UIScreen mainScreen];
         });
     }
-#endif
 }
+#endif
 
 - (void)layoutSubviews
 {
@@ -234,9 +231,10 @@
 @synthesize preferredStatusBarStyle;
 #endif
 
-- (instancetype)initWithQIOSScreen:(QT_PREPEND_NAMESPACE(QIOSScreen) *)screen
+- (instancetype)initWithWindow:(UIWindow*)window andScreen:(QT_PREPEND_NAMESPACE(QIOSScreen) *)screen
 {
     if (self = [self init]) {
+        self.window = window;
         self.platformScreen = screen;
 
         self.changingOrientation = NO;
@@ -297,6 +295,15 @@
             name:UIApplicationDidChangeStatusBarOrientationNotification
             object:qt_apple_sharedApplication()];
 #endif
+
+    // Make sure any top level windows that have already been created
+    // for this screen are reparented into our desktop manager view.
+    for (auto *window : qGuiApp->topLevelWindows()) {
+        if (window->screen()->handle() != self.platformScreen)
+            continue;
+        if (auto *platformWindow = window->handle())
+            platformWindow->setParent(nullptr);
+    }
 }
 
 - (void)viewDidUnload