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, 27 insertions, 0 deletions

diff --git a/src/plugins/platforms/ios/qiosglobal.mm b/src/plugins/platforms/ios/qiosglobal.mm
index eb9e713b0d..25ccf2961b 100644
--- a/src/plugins/platforms/ios/qiosglobal.mm
+++ b/src/plugins/platforms/ios/qiosglobal.mm
@@ -13,6 +13,7 @@ QT_BEGIN_NAMESPACE
 Q_LOGGING_CATEGORY(lcQpaApplication, "qt.qpa.application");
 Q_LOGGING_CATEGORY(lcQpaInputMethods, "qt.qpa.input.methods");
 Q_LOGGING_CATEGORY(lcQpaWindow, "qt.qpa.window");
+Q_LOGGING_CATEGORY(lcQpaWindowScene, "qt.qpa.window.scene");
 
 bool isQtApplication()
 {
@@ -109,6 +110,32 @@ UIWindow *presentationWindow(QWindow *window)
     return uiWindow;
 }
 
+UIView *rootViewForScreen(QScreen *screen)
+{
+    const auto *iosScreen = static_cast<QIOSScreen *>(screen->handle());
+    for (UIScene *scene in [qt_apple_sharedApplication().connectedScenes allObjects]) {
+        if (![scene isKindOfClass:UIWindowScene.class])
+            continue;
+
+        auto *windowScene = static_cast<UIWindowScene*>(scene);
+
+#if !defined(Q_OS_VISIONOS)
+        if (windowScene.screen != iosScreen->uiScreen())
+            continue;
+#else
+        Q_UNUSED(iosScreen);
+#endif
+
+        UIWindow *uiWindow = windowScene.keyWindow;
+        if (!uiWindow && windowScene.windows.count)
+            uiWindow = windowScene.windows[0];
+
+        return uiWindow.rootViewController.view;
+    }
+
+    return nullptr;
+}
+
 QT_END_NAMESPACE
 
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