Avoid passing nil to IOS accessibility announcement

shell/platform/darwin/ios/framework/Source/accessibility_bridge.h

@@ -77,6 +77,7 @@ class AccessibilityBridge final : public AccessibilityBridgeIos {
 
  private:
   SemanticsObject* GetOrCreateObject(int32_t id, flutter::SemanticsNodeUpdates& updates);
+  SemanticsObject* FindFirstFocusable(SemanticsObject* object);
   void VisitObjectsRecursivelyAndRemove(SemanticsObject* object,
                                         NSMutableArray<NSNumber*>* doomed_uids);
   void HandleEvent(NSDictionary<NSString*, id>* annotatedEvent);

shell/platform/darwin/ios/framework/Source/accessibility_bridge.mm

@@ -187,22 +187,36 @@ void PostAccessibilityNotification(UIAccessibilityNotifications notification,
   [objects_ removeObjectsForKeys:doomed_uids];
 
   layoutChanged = layoutChanged || [doomed_uids count] > 0;
+  // We should send out only one notification per semantics update.
   if (routeChanged) {
     if (!ios_delegate_->IsFlutterViewControllerPresentingModalViewController(view_controller_)) {
+      SemanticsObject* nextToFocus = [lastAdded routeFocusObject];
+      if (!nextToFocus && root) {
+        nextToFocus = FindFirstFocusable(root);
+      }
       ios_delegate_->PostAccessibilityNotification(UIAccessibilityScreenChangedNotification,
-                                                   [lastAdded routeFocusObject]);
+                                                   nextToFocus);
     }
   } else if (layoutChanged) {
     // Tries to refocus the previous focused semantics object to avoid random jumps.
-    ios_delegate_->PostAccessibilityNotification(
-        UIAccessibilityLayoutChangedNotification,
-        [objects_.get() objectForKey:@(last_focused_semantics_object_id_)]);
-  }
-  if (scrollOccured) {
-    // Tries to refocus the previous focused semantics object to avoid random jumps.
-    ios_delegate_->PostAccessibilityNotification(
-        UIAccessibilityPageScrolledNotification,
-        [objects_.get() objectForKey:@(last_focused_semantics_object_id_)]);
+    SemanticsObject* nextToFocus =
+        [objects_.get() objectForKey:@(last_focused_semantics_object_id_)];
+    if (!nextToFocus && root) {
+      nextToFocus = FindFirstFocusable(root);
+    }
+    ios_delegate_->PostAccessibilityNotification(UIAccessibilityLayoutChangedNotification,
+                                                 nextToFocus);
+  } else if (scrollOccured) {
+    // TODO(chunhtai): figure out what string to use for notification. At this
+    // point, it is guarantee the previous focused object is still in the tree
+    // so that we don't need to worry about focus lost. (e.g. "Screen 0 of 3")
+    SemanticsObject* nextToFocus =
+        [objects_.get() objectForKey:@(last_focused_semantics_object_id_)];
+    if (!nextToFocus && root) {
+      nextToFocus = FindFirstFocusable(root);
+    }
+    ios_delegate_->PostAccessibilityNotification(UIAccessibilityPageScrolledNotification,
+                                                 nextToFocus);
   }
 }
 
@@ -286,6 +300,21 @@ static bool DidFlagChange(const flutter::SemanticsNode& oldNode,
     VisitObjectsRecursivelyAndRemove(child, doomed_uids);
 }
 
+SemanticsObject* AccessibilityBridge::FindFirstFocusable(SemanticsObject* object) {
+  if (object.isAccessibilityElement) {
+    return object;
+  }
+
+  SemanticsObject* candidate = nil;
+  for (SemanticsObject* child in [object children]) {
+    if (candidate) {
+      break;
+    }
+    candidate = FindFirstFocusable(child);
+  }
+  return candidate;
+}
+
 void AccessibilityBridge::HandleEvent(NSDictionary<NSString*, id>* annotatedEvent) {
   NSString* type = annotatedEvent[@"type"];
   if ([type isEqualToString:@"announce"]) {

shell/platform/darwin/ios/framework/Source/accessibility_bridge_test.mm

@@ -283,7 +283,6 @@ - (void)testAnnouncesRouteChanges {
   id mockFlutterView = OCMClassMock([FlutterView class]);
   id mockFlutterViewController = OCMClassMock([FlutterViewController class]);
   OCMStub([mockFlutterViewController view]).andReturn(mockFlutterView);
-  std::string label = "some label";
 
   NSMutableArray<NSDictionary<NSString*, id>*>* accessibility_notifications =
       [[[NSMutableArray alloc] init] autorelease];
@@ -304,24 +303,100 @@ - (void)testAnnouncesRouteChanges {
   flutter::CustomAccessibilityActionUpdates actions;
   flutter::SemanticsNodeUpdates nodes;
 
-  flutter::SemanticsNode route_node;
-  route_node.id = 1;
-  route_node.flags = static_cast<int32_t>(flutter::SemanticsFlags::kScopesRoute) |
-                     static_cast<int32_t>(flutter::SemanticsFlags::kNamesRoute);
-  route_node.label = "route";
-  nodes[route_node.id] = route_node;
+  flutter::SemanticsNode node1;
+  node1.id = 1;
+  node1.label = "node1";
+  node1.flags = static_cast<int32_t>(flutter::SemanticsFlags::kScopesRoute);
+  node1.childrenInTraversalOrder = {2, 3};
+  node1.childrenInHitTestOrder = {2, 3};
+  nodes[node1.id] = node1;
+  flutter::SemanticsNode node2;
+  node2.id = 2;
+  node2.label = "node2";
+  nodes[node2.id] = node2;
+  flutter::SemanticsNode node3;
+  node3.id = 3;
+  node3.flags = static_cast<int32_t>(flutter::SemanticsFlags::kNamesRoute);
+  node3.label = "node3";
+  nodes[node3.id] = node3;
   flutter::SemanticsNode root_node;
   root_node.id = kRootNodeId;
-  root_node.label = label;
+  root_node.flags = static_cast<int32_t>(flutter::SemanticsFlags::kScopesRoute);
   root_node.childrenInTraversalOrder = {1};
   root_node.childrenInHitTestOrder = {1};
   nodes[root_node.id] = root_node;
   bridge->UpdateSemantics(/*nodes=*/nodes, /*actions=*/actions);
 
   XCTAssertEqual([accessibility_notifications count], 1ul);
   SemanticsObject* focusObject = accessibility_notifications[0][@"argument"];
-  XCTAssertEqual([focusObject uid], 1);
-  XCTAssertEqualObjects([focusObject accessibilityLabel], @"route");
+  XCTAssertEqual([focusObject uid], 3);
+  XCTAssertEqualObjects([focusObject accessibilityLabel], @"node3");
+  XCTAssertEqual([accessibility_notifications[0][@"notification"] unsignedIntValue],
+                 UIAccessibilityScreenChangedNotification);
+}
+
+- (void)testAnnouncesRouteChangesWhenNoNamesRoute {
+  flutter::MockDelegate mock_delegate;
+  auto thread_task_runner = CreateNewThread("AccessibilityBridgeTest");
+  flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
+                               /*platform=*/thread_task_runner,
+                               /*raster=*/thread_task_runner,
+                               /*ui=*/thread_task_runner,
+                               /*io=*/thread_task_runner);
+  auto platform_view = std::make_unique<flutter::PlatformViewIOS>(
+      /*delegate=*/mock_delegate,
+      /*rendering_api=*/flutter::IOSRenderingAPI::kSoftware,
+      /*task_runners=*/runners);
+  id mockFlutterView = OCMClassMock([FlutterView class]);
+  id mockFlutterViewController = OCMClassMock([FlutterViewController class]);
+  OCMStub([mockFlutterViewController view]).andReturn(mockFlutterView);
+
+  NSMutableArray<NSDictionary<NSString*, id>*>* accessibility_notifications =
+      [[[NSMutableArray alloc] init] autorelease];
+  auto ios_delegate = std::make_unique<flutter::MockIosDelegate>();
+  ios_delegate->on_PostAccessibilityNotification_ =
+      [accessibility_notifications](UIAccessibilityNotifications notification, id argument) {
+        [accessibility_notifications addObject:@{
+          @"notification" : @(notification),
+          @"argument" : argument ? argument : [NSNull null],
+        }];
+      };
+  __block auto bridge =
+      std::make_unique<flutter::AccessibilityBridge>(/*view_controller=*/mockFlutterViewController,
+                                                     /*platform_view=*/platform_view.get(),
+                                                     /*platform_views_controller=*/nil,
+                                                     /*ios_delegate=*/std::move(ios_delegate));
+
+  flutter::CustomAccessibilityActionUpdates actions;
+  flutter::SemanticsNodeUpdates nodes;
+
+  flutter::SemanticsNode node1;
+  node1.id = 1;
+  node1.label = "node1";
+  node1.flags = static_cast<int32_t>(flutter::SemanticsFlags::kScopesRoute);
+  node1.childrenInTraversalOrder = {2, 3};
+  node1.childrenInHitTestOrder = {2, 3};
+  nodes[node1.id] = node1;
+  flutter::SemanticsNode node2;
+  node2.id = 2;
+  node2.label = "node2";
+  nodes[node2.id] = node2;
+  flutter::SemanticsNode node3;
+  node3.id = 3;
+  node3.label = "node3";
+  nodes[node3.id] = node3;
+  flutter::SemanticsNode root_node;
+  root_node.id = kRootNodeId;
+  root_node.childrenInTraversalOrder = {1};
+  root_node.childrenInHitTestOrder = {1};
+  nodes[root_node.id] = root_node;
+  bridge->UpdateSemantics(/*nodes=*/nodes, /*actions=*/actions);
+
+  // Notification should focus first focusable node, which is node1.
+  XCTAssertEqual([accessibility_notifications count], 1ul);
+  SemanticsObject* focusObject = accessibility_notifications[0][@"argument"];
+  XCTAssertEqual([focusObject uid], 2);
+  XCTAssertEqualObjects([focusObject accessibilityLabel], @"node2");
   XCTAssertEqual([accessibility_notifications[0][@"notification"] unsignedIntValue],
                  UIAccessibilityScreenChangedNotification);
 }
@@ -384,9 +459,10 @@ - (void)testAnnouncesLayoutChangeWithNilIfLastFocusIsRemoved {
   new_root_node.label = "root";
   second_update[root_node.id] = new_root_node;
   bridge->UpdateSemantics(/*nodes=*/second_update, /*actions=*/actions);
-  NSNull* focusObject = accessibility_notifications[0][@"argument"];
-  // The node 1 was removed, so the bridge will set the focus object to nil.
-  XCTAssertEqual(focusObject, [NSNull null]);
+  SemanticsObject* focusObject = accessibility_notifications[0][@"argument"];
+  // The node 1 was removed, so the bridge will set the focus object to root.
+  XCTAssertEqual([focusObject uid], 0);
+  XCTAssertEqualObjects([focusObject accessibilityLabel], @"root");
   XCTAssertEqual([accessibility_notifications[0][@"notification"] unsignedIntValue],
                  UIAccessibilityLayoutChangedNotification);
 }