fix ios layout change cause the accessibility focus to jump randomly.

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

@@ -453,6 +453,7 @@ - (BOOL)accessibilityPerformEscape {
 - (void)accessibilityElementDidBecomeFocused {
   if (![self isAccessibilityBridgeAlive])
     return;
+  [self bridge]->AccessibilityFocusDidChange([self uid]);
   if ([self node].HasFlag(flutter::SemanticsFlags::kIsHidden) ||
       [self node].HasFlag(flutter::SemanticsFlags::kIsHeader)) {
     [self bridge]->DispatchSemanticsAction([self uid], flutter::SemanticsAction::kShowOnScreen);

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

@@ -33,6 +33,7 @@ void DispatchSemanticsAction(int32_t id,
     SemanticsActionObservation observation(id, action);
     observations.push_back(observation);
   }
+  void AccessibilityFocusDidChange(int32_t id) override {}
   FlutterPlatformViewsController* GetPlatformViewsController() const override { return nil; }
   std::vector<SemanticsActionObservation> observations;
 

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

@@ -61,6 +61,7 @@ class AccessibilityBridge final : public AccessibilityBridgeIos {
   void DispatchSemanticsAction(int32_t id,
                                flutter::SemanticsAction action,
                                std::vector<uint8_t> args) override;
+  void AccessibilityFocusDidChange(int32_t id) override;
 
   UIView<UITextInput>* textInputView() override;
 
@@ -83,6 +84,7 @@ class AccessibilityBridge final : public AccessibilityBridgeIos {
   FlutterViewController* view_controller_;
   PlatformViewIOS* platform_view_;
   FlutterPlatformViewsController* platform_views_controller_;
+  int32_t last_focused_semantics_object_id_;
   fml::scoped_nsobject<NSMutableDictionary<NSNumber*, SemanticsObject*>> objects_;
   fml::scoped_nsprotocol<FlutterBasicMessageChannel*> accessibility_channel_;
   fml::WeakPtrFactory<AccessibilityBridge> weak_factory_;

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

@@ -41,6 +41,7 @@ void PostAccessibilityNotification(UIAccessibilityNotifications notification,
     : view_controller_(view_controller),
       platform_view_(platform_view),
       platform_views_controller_(platform_views_controller),
+      last_focused_semantics_object_id_(0),
       objects_([[NSMutableDictionary alloc] init]),
       weak_factory_(this),
       previous_route_id_(0),
@@ -66,6 +67,10 @@ void PostAccessibilityNotification(UIAccessibilityNotifications notification,
   return [[platform_view_->GetOwnerViewController().get().engine textInputPlugin] textInputView];
 }
 
+void AccessibilityBridge::AccessibilityFocusDidChange(int32_t id) {
+  last_focused_semantics_object_id_ = id;
+}
+
 void AccessibilityBridge::UpdateSemantics(flutter::SemanticsNodeUpdates nodes,
                                           flutter::CustomAccessibilityActionUpdates actions) {
   BOOL layoutChanged = NO;
@@ -188,12 +193,16 @@ void PostAccessibilityNotification(UIAccessibilityNotifications notification,
                                                    [lastAdded routeFocusObject]);
     }
   } else if (layoutChanged) {
-    // TODO(goderbauer): figure out which node to focus next.
-    ios_delegate_->PostAccessibilityNotification(UIAccessibilityLayoutChangedNotification, nil);
+    // 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) {
-    // TODO(tvolkert): provide meaningful string (e.g. "page 2 of 5")
-    ios_delegate_->PostAccessibilityNotification(UIAccessibilityPageScrolledNotification, @"");
+    // Tries to refocus the previous focused semantics object to avoid random jumps.
+    ios_delegate_->PostAccessibilityNotification(
+        UIAccessibilityPageScrolledNotification,
+        [objects_.get() objectForKey:@(last_focused_semantics_object_id_)]);
   }
 }
 

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

@@ -24,6 +24,13 @@ class AccessibilityBridgeIos {
   virtual void DispatchSemanticsAction(int32_t id,
                                        flutter::SemanticsAction action,
                                        std::vector<uint8_t> args) = 0;
+  /**
+   * A callback that is called after the accessibility focus has moved to a new
+   * SemanticObject.
+   *
+   * The input id is the uid of the newly focused SemanticObject.
+   */
+  virtual void AccessibilityFocusDidChange(int32_t id) = 0;
   virtual FlutterPlatformViewsController* GetPlatformViewsController() const = 0;
 };
 

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

@@ -306,7 +306,6 @@ - (void)testAnnouncesRouteChanges {
 
   flutter::SemanticsNode route_node;
   route_node.id = 1;
-  route_node.label = label;
   route_node.flags = static_cast<int32_t>(flutter::SemanticsFlags::kScopesRoute) |
                      static_cast<int32_t>(flutter::SemanticsFlags::kNamesRoute);
   route_node.label = "route";
@@ -327,6 +326,207 @@ - (void)testAnnouncesRouteChanges {
                  UIAccessibilityScreenChangedNotification);
 }
 
+- (void)testAnnouncesLayoutChangeWithNilIfLastFocusIsRemoved {
+  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]);
+
+  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=*/mockFlutterView,
+                                                     /*platform_view=*/platform_view.get(),
+                                                     /*platform_views_controller=*/nil,
+                                                     /*ios_delegate=*/std::move(ios_delegate));
+
+  flutter::CustomAccessibilityActionUpdates actions;
+  flutter::SemanticsNodeUpdates first_update;
+
+  flutter::SemanticsNode route_node;
+  route_node.id = 1;
+  route_node.label = "route";
+  first_update[route_node.id] = route_node;
+  flutter::SemanticsNode root_node;
+  root_node.id = kRootNodeId;
+  root_node.label = "root";
+  root_node.childrenInTraversalOrder = {1};
+  root_node.childrenInHitTestOrder = {1};
+  first_update[root_node.id] = root_node;
+  bridge->UpdateSemantics(/*nodes=*/first_update, /*actions=*/actions);
+
+  XCTAssertEqual([accessibility_notifications count], 0ul);
+  // Simulates the focusing on the node 1.
+  bridge->AccessibilityFocusDidChange(1);
+
+  flutter::SemanticsNodeUpdates second_update;
+  // Simulates the removal of the node 1
+  flutter::SemanticsNode new_root_node;
+  new_root_node.id = kRootNodeId;
+  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]);
+  XCTAssertEqual([accessibility_notifications[0][@"notification"] unsignedIntValue],
+                 UIAccessibilityLayoutChangedNotification);
+}
+
+- (void)testAnnouncesLayoutChangeWithLastFocused {
+  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]);
+
+  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=*/mockFlutterView,
+                                                     /*platform_view=*/platform_view.get(),
+                                                     /*platform_views_controller=*/nil,
+                                                     /*ios_delegate=*/std::move(ios_delegate));
+
+  flutter::CustomAccessibilityActionUpdates actions;
+  flutter::SemanticsNodeUpdates first_update;
+
+  flutter::SemanticsNode node_one;
+  node_one.id = 1;
+  node_one.label = "route1";
+  first_update[node_one.id] = node_one;
+  flutter::SemanticsNode node_two;
+  node_two.id = 2;
+  node_two.label = "route2";
+  first_update[node_two.id] = node_two;
+  flutter::SemanticsNode root_node;
+  root_node.id = kRootNodeId;
+  root_node.label = "root";
+  root_node.childrenInTraversalOrder = {1, 2};
+  root_node.childrenInHitTestOrder = {1, 2};
+  first_update[root_node.id] = root_node;
+  bridge->UpdateSemantics(/*nodes=*/first_update, /*actions=*/actions);
+
+  XCTAssertEqual([accessibility_notifications count], 0ul);
+  // Simulates the focusing on the node 1.
+  bridge->AccessibilityFocusDidChange(1);
+
+  flutter::SemanticsNodeUpdates second_update;
+  // Simulates the removal of the node 2.
+  flutter::SemanticsNode new_root_node;
+  new_root_node.id = kRootNodeId;
+  new_root_node.label = "root";
+  new_root_node.childrenInTraversalOrder = {1};
+  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);
+  XCTAssertEqual([accessibility_notifications[0][@"notification"] unsignedIntValue],
+                 UIAccessibilityLayoutChangedNotification);
+}
+
+- (void)testAnnouncesScrollChangeWithLastFocused {
+  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]);
+
+  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=*/mockFlutterView,
+                                                     /*platform_view=*/platform_view.get(),
+                                                     /*platform_views_controller=*/nil,
+                                                     /*ios_delegate=*/std::move(ios_delegate));
+
+  flutter::CustomAccessibilityActionUpdates actions;
+  flutter::SemanticsNodeUpdates first_update;
+
+  flutter::SemanticsNode node_one;
+  node_one.id = 1;
+  node_one.label = "route1";
+  node_one.scrollPosition = 0.0;
+  first_update[node_one.id] = node_one;
+  flutter::SemanticsNode root_node;
+  root_node.id = kRootNodeId;
+  root_node.label = "root";
+  root_node.childrenInTraversalOrder = {1};
+  root_node.childrenInHitTestOrder = {1};
+  first_update[root_node.id] = root_node;
+  bridge->UpdateSemantics(/*nodes=*/first_update, /*actions=*/actions);
+
+  // The first update will trigger a scroll announcement, but we are not interested in it.
+  [accessibility_notifications removeAllObjects];
+
+  // Simulates the focusing on the node 1.
+  bridge->AccessibilityFocusDidChange(1);
+
+  flutter::SemanticsNodeUpdates second_update;
+  // Simulates the scrolling on the node 1.
+  flutter::SemanticsNode new_node_one;
+  new_node_one.id = 1;
+  new_node_one.label = "route1";
+  new_node_one.scrollPosition = 1.0;
+  second_update[new_node_one.id] = new_node_one;
+  bridge->UpdateSemantics(/*nodes=*/second_update, /*actions=*/actions);
+  SemanticsObject* focusObject = accessibility_notifications[0][@"argument"];
+  // Since we have focused on the node 1 right before the scrolling, the bridge should refocus the
+  // node 1.
+  XCTAssertEqual([focusObject uid], 1);
+  XCTAssertEqual([accessibility_notifications[0][@"notification"] unsignedIntValue],
+                 UIAccessibilityPageScrolledNotification);
+}
+
 - (void)testAnnouncesIgnoresRouteChangesWhenModal {
   flutter::MockDelegate mock_delegate;
   auto thread_task_runner = CreateNewThread("AccessibilityBridgeTest");