iOS a11y: Ensure parent elements are stacked below their children

The accessibility system on iOS does not support elements that are both
accessible themselves, and act as a container for other elements. You
either return YES from isAccessibilityElement, which allows you to
report accessible properties for the element, or NO, in which case
you can implement the informal UIAccessibilityContainer protocol
to report child elements. This was confirmed in Apple Q&A session
on accessibility December 14.

As Qt's accessibility system allow elements that are both containers
and have properties of their own, we can't build a hierarchy of elements
and containers, with only the leaf elements being accessible. Instead,
we let each UIView act as a UIAccessibilityContainer, and report the
entire child hierarchy as a single level of sibling accessible elements.

In doing so, we include elements such as the Window or Dialog that
root all the accessible elements. And apparently the order that we
report these elements back to iOS determine the z-order of the
elements, so we need to ensure "container" elements are behind
their children. Otherwise assistive technologies such as Voice Control,
or the Accessibility Inspector, will not be able to target the child
elements.

Fixes: QTBUG-108848
Pick-to: 6.2 6.4 6.5 5.15
Change-Id: I5234bab2f14d5f368ae8c2672b051efcb80aa77d
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

1 files changed, 3 insertions, 1 deletions

diff --git a/src/plugins/platforms/ios/quiview_accessibility.mm b/src/plugins/platforms/ios/quiview_accessibility.mm
index bb27d832d1..366141ef81 100644
--- a/src/plugins/platforms/ios/quiview_accessibility.mm
+++ b/src/plugins/platforms/ios/quiview_accessibility.mm
@@ -23,9 +23,11 @@
     if (!iface || iface->state().invisible)
         return;
 
-    [self createAccessibleElement: iface];
     for (int i = 0; i < iface->childCount(); ++i)
         [self createAccessibleContainer: iface->child(i)];
+
+    // The container element must go last, so that it underlays all its children
+    [self createAccessibleElement:iface];
 }
 
 - (void)initAccessibility