iOS Accessibility: during layout change, only specify the focus object when it is changed. (#33972)

Author: Chris Yang

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

@@ -211,9 +211,15 @@ void PostAccessibilityNotification(UIAccessibilityNotifications notification,
     }
 
     if (layoutChanged) {
+      SemanticsObject* next = FindNextFocusableIfNecessary();
+      SemanticsObject* lastFocused =
+          [objects_.get() objectForKey:@(last_focused_semantics_object_id_)];
+      // Only specify the focus item if the new focus is different, avoiding double focuses on the
+      // same item. See: https://github.com/flutter/flutter/issues/104176. If there is a route
+      // change, we always refocus.
       ios_delegate_->PostAccessibilityNotification(
           UIAccessibilityLayoutChangedNotification,
-          FindNextFocusableIfNecessary().nativeAccessibility);
+          (routeChanged || next != lastFocused) ? next.nativeAccessibility : NULL);
     } 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
@@ -327,11 +333,9 @@ static bool DidFlagChange(const flutter::SemanticsNode& oldNode,
 
 SemanticsObject* AccessibilityBridge::FindFirstFocusable(SemanticsObject* parent) {
   SemanticsObject* currentObject = parent ?: objects_.get()[@(kRootNodeId)];
-  ;
   if (!currentObject) {
     return nil;
   }
-
   if (currentObject.isAccessibilityElement) {
     return currentObject;
   }

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

@@ -743,10 +743,83 @@ - (void)testLayoutChangeDoesCallNativeAccessibility {
   bridge->UpdateSemantics(/*nodes=*/new_nodes, /*actions=*/new_actions);
 
   XCTAssertEqual([accessibility_notifications count], 1ul);
-  SemanticsObject* focusObject = accessibility_notifications[0][@"argument"];
-  // Make sure refocus event is sent with the nativeAccessibility of root node
-  // which is a FlutterSemanticsScrollView.
-  XCTAssertTrue([focusObject isKindOfClass:[FlutterSemanticsScrollView class]]);
+  id focusObject = accessibility_notifications[0][@"argument"];
+
+  // Make sure the focused item is not specificed when it stays the same.
+  // See: https://github.com/flutter/flutter/issues/104176
+  XCTAssertEqualObjects(focusObject, [NSNull null]);
+  XCTAssertEqual([accessibility_notifications[0][@"notification"] unsignedIntValue],
+                 UIAccessibilityLayoutChangedNotification);
+}
+
+- (void)testLayoutChangeDoesCallNativeAccessibilityWhenFocusChanged {
+  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,
+      /*platform_views_controller=*/nil,
+      /*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";
+  nodes[node1.id] = node1;
+  flutter::SemanticsNode root_node;
+  root_node.id = kRootNodeId;
+  root_node.label = "root";
+  root_node.flags = static_cast<int32_t>(flutter::SemanticsFlags::kHasImplicitScrolling);
+  root_node.childrenInTraversalOrder = {1};
+  root_node.childrenInHitTestOrder = {1};
+  nodes[root_node.id] = root_node;
+  bridge->UpdateSemantics(/*nodes=*/nodes, /*actions=*/actions);
+
+  // Simulates the focusing on the node 1.
+  bridge->AccessibilityObjectDidBecomeFocused(1);
+
+  // Remove node 1 to trigger a layout change notification, and focus should be one root
+  flutter::CustomAccessibilityActionUpdates new_actions;
+  flutter::SemanticsNodeUpdates new_nodes;
+
+  flutter::SemanticsNode new_root_node;
+  new_root_node.id = kRootNodeId;
+  new_root_node.label = "root";
+  new_root_node.flags = static_cast<int32_t>(flutter::SemanticsFlags::kHasImplicitScrolling);
+  new_nodes[new_root_node.id] = new_root_node;
+  bridge->UpdateSemantics(/*nodes=*/new_nodes, /*actions=*/new_actions);
+
+  XCTAssertEqual([accessibility_notifications count], 1ul);
+  SemanticsObject* focusObject2 = accessibility_notifications[0][@"argument"];
+
+  // Bridge should ask accessibility to focus on root because node 1 is moved from screen.
+  XCTAssertTrue([focusObject2 isKindOfClass:[FlutterSemanticsScrollView class]]);
   XCTAssertEqual([accessibility_notifications[0][@"notification"] unsignedIntValue],
                  UIAccessibilityLayoutChangedNotification);
 }
@@ -896,7 +969,6 @@ - (void)testAnnouncesRouteChangesAndLayoutChangeInOneUpdate {
   XCTAssertEqual([accessibility_notifications[1][@"notification"] unsignedIntValue],
                  UIAccessibilityScreenChangedNotification);
   SemanticsObject* focusObject = accessibility_notifications[2][@"argument"];
-  // It should still focus the root.
   XCTAssertEqual([focusObject uid], 0);
   XCTAssertEqual([accessibility_notifications[2][@"notification"] unsignedIntValue],
                  UIAccessibilityLayoutChangedNotification);
@@ -1211,7 +1283,7 @@ - (void)testAnnouncesLayoutChangeWithNilIfLastFocusIsRemoved {
                  UIAccessibilityLayoutChangedNotification);
 }
 
-- (void)testAnnouncesLayoutChangeWithLastFocused {
+- (void)testAnnouncesLayoutChangeWithTheSameItemFocused {
   flutter::MockDelegate mock_delegate;
   auto thread_task_runner = CreateNewThread("AccessibilityBridgeTest");
   flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
@@ -1276,10 +1348,10 @@ - (void)testAnnouncesLayoutChangeWithLastFocused {
   new_root_node.childrenInHitTestOrder = {1};
   second_update[root_node.id] = new_root_node;
   bridge->UpdateSemantics(/*nodes=*/second_update, /*actions=*/actions);
-  SemanticsObject* focusObject = accessibility_notifications[0][@"argument"];
-  // Since we have focused on the node 1 right before the layout changed, the bridge should refocus
-  // the node 1.
-  XCTAssertEqual([focusObject uid], 1);
+  id focusObject = accessibility_notifications[0][@"argument"];
+  // Since we have focused on the node 1 right before the layout changed, the bridge should not ask
+  // to refocus again on the same node.
+  XCTAssertEqualObjects(focusObject, [NSNull null]);
   XCTAssertEqual([accessibility_notifications[0][@"notification"] unsignedIntValue],
                  UIAccessibilityLayoutChangedNotification);
 }