iOS: Propagate focus changes to VoiceOver

Changing the focus object should update the VoiceOver focused element,
the same way we do it on macOS.

There's no NSAccessibilityFocusedUIElementChangedNotification on iOS,
but we can pass the focused element as an argument when posting the
UIAccessibilityLayoutChangedNotification.

The class method on QMacAccessibilityElement to get an element for
an QAccessible::Id was not used by any callers, and has been modified
to resolve the container from the QAccessibleInterface, so that we
don't need to plumb that all the way from the focus change event.

Inspired-by: Jan Möller <jan.moeller@governikus.de>
Fixes: QTBUG-114608
Pick-to: 6.5
Change-Id: I2e43ae649bc7e3a44c1e1200e8de66bf420b1949
Reviewed-by: Lars Schmertmann <lars.schmertmann@governikus.de>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 7a512d1)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 1c8cb94)

src/plugins/platforms/ios/qiosplatformaccessibility.mm

@@ -7,6 +7,7 @@
 
 #include <QtGui/QtGui>
 #include "qioswindow.h"
+#include "quiaccessibilityelement.h"
 
 QIOSPlatformAccessibility::QIOSPlatformAccessibility()
 {}
@@ -40,6 +41,16 @@ void invalidateCache(QAccessibleInterface *iface)
     if (!isActive() || !accessibleInterface)
         return;
     switch (event->type()) {
+    case QAccessible::Focus: {
+        auto *element = [QMacAccessibilityElement elementWithId:event->uniqueId()];
+        Q_ASSERT(element);
+        // There's no NSAccessibilityFocusedUIElementChangedNotification, like we have on
+        // macOS. Instead, the documentation for UIAccessibilityLayoutChangedNotification
+        // specifies that the optional argument to UIAccessibilityPostNotification is the
+        // accessibility element for VoiceOver to move to after processing the notification.
+        UIAccessibilityPostNotification(UIAccessibilityLayoutChangedNotification, element);
+        break;
+    }
     case QAccessible::ObjectCreated:
     case QAccessible::ObjectShow:
     case QAccessible::ObjectHide:

src/plugins/platforms/ios/qioswindow.h

@@ -63,6 +63,7 @@ class QIOSWindow : public QObject, public QPlatformWindow
 #endif
 
     bool isForeignWindow() const override;
+    UIView *view() const;
 
 private:
     void applicationStateChanged(Qt::ApplicationState state);

src/plugins/platforms/ios/qioswindow.mm

@@ -456,6 +456,11 @@
     return ![m_view isKindOfClass:QUIView.class];
 }
 
+UIView *QIOSWindow::view() const
+{
+    return m_view;
+}
+
 QT_END_NAMESPACE
 
 #include "moc_qioswindow.cpp"

src/plugins/platforms/ios/quiaccessibilityelement.h

@@ -14,7 +14,7 @@
 @property (readonly) QAccessible::Id axid;
 
 - (instancetype)initWithId:(QAccessible::Id)anId withAccessibilityContainer:(id)view;
-+ (instancetype)elementWithId:(QAccessible::Id)anId withAccessibilityContainer:(id)view;
++ (instancetype)elementWithId:(QAccessible::Id)anId;
 
 @end
 

src/plugins/platforms/ios/quiaccessibilityelement.mm

@@ -8,6 +8,7 @@
 #include "private/qaccessiblecache_p.h"
 #include "private/qcore_mac_p.h"
 #include "uistrings_p.h"
+#include "qioswindow.h"
 
 QT_NAMESPACE_ALIAS_OBJC_CLASS(QMacAccessibilityElement);
 
@@ -23,7 +24,7 @@ - (instancetype)initWithId:(QAccessible::Id)anId withAccessibilityContainer:(id)
     return self;
 }
 
-+ (instancetype)elementWithId:(QAccessible::Id)anId withAccessibilityContainer:(id)view
++ (instancetype)elementWithId:(QAccessible::Id)anId
 {
     Q_ASSERT(anId);
     if (!anId)
@@ -33,9 +34,17 @@ + (instancetype)elementWithId:(QAccessible::Id)anId withAccessibilityContainer:(
 
     QMacAccessibilityElement *element = cache->elementForId(anId);
     if (!element) {
-        Q_ASSERT(QAccessible::accessibleInterface(anId));
-        element = [[self alloc] initWithId:anId withAccessibilityContainer:view];
-        cache->insertElement(anId, element);
+        auto *a11yInterface = QAccessible::accessibleInterface(anId);
+        Q_ASSERT(a11yInterface);
+        auto *window = a11yInterface->window();
+        if (window && window->handle()) {
+            auto *platformWindow = static_cast<QIOSWindow*>(window->handle());
+            element = [[self alloc] initWithId:anId withAccessibilityContainer:platformWindow->view()];
+            cache->insertElement(anId, element);
+        } else {
+            qWarning() << "Could not create a11y element for" << window
+                << "with platform window" << (window ? window->handle() : nullptr);
+        }
     }
     return element;
 }