QWindow: Persist foreign winId to support destroy/create cycles

We used to set a private _q_foreignWinId property on QWindow when
creating foreign windows, and this was the mechanism which we then
passed the foreign winId to the platform plugin.

With c585802e946d97e7d177ea334a162dc7bc286b84 this was removed,
since we now were passing the winId through via explicit QPA
APIs, and since 0c6911e5cde24c45d6f2c08b6e71064bdd1eccfa removed
the ability to explicitly destroy() a foreign window.

But when closing a QWindow, we destroy both the window itself,
and all its children, including foreign windows. In this case
we still want to support recreating the foreign window, for
example when the parent window is shown again. To enable this
we restore the _q_foreignWinId private property, but keep
the limitation of not being able to explicitly destroy a
foreign window.

Pick-to: 6.7 6.5
Fixes: QTBUG-124160
Change-Id: Ia885ba9f043e64fb21eedd2b4c344679726f1b5c
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/plugins/platforms/ios/qioswindow.mm b/src/plugins/platforms/ios/qioswindow.mm
index 6a25e24c2d..90e955b90b 100644
--- a/src/plugins/platforms/ios/qioswindow.mm
+++ b/src/plugins/platforms/ios/qioswindow.mm
@@ -55,7 +55,8 @@ QIOSWindow::QIOSWindow(QWindow *window, WId nativeHandle)
 
     connect(qGuiApp, &QGuiApplication::applicationStateChanged, this, &QIOSWindow::applicationStateChanged);
 
-    setParent(QPlatformWindow::parent());
+    if (QPlatformWindow::parent())
+        setParent(QPlatformWindow::parent());
 
     if (!isForeignWindow()) {
         // Resolve default window geometry in case it was not set before creating the