Overrides accessibilityScrollToVisible (#42047)

fixes flutter/flutter#61624

Observed behavior is that this method is called when an item is swipe-to-focusd in VoiceOver.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: chunhtai

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

@@ -460,6 +460,10 @@ - (NSAttributedString*)createAttributedStringFromString:(NSString*)string
   return attributedString;
 }
 
+- (void)showOnScreen {
+  [self bridge]->DispatchSemanticsAction([self uid], flutter::SemanticsAction::kShowOnScreen);
+}
+
 #pragma mark - UIAccessibility overrides
 
 - (BOOL)isAccessibilityElement {
@@ -561,14 +565,32 @@ - (SemanticsObject*)search:(CGPoint)point {
   return nil;
 }
 
-// Overrides apple private method to fix https://github.com/flutter/flutter/issues/113377.
-// For overlapping UIAccessibilityElements (e.g. a stack) in IOS, the focus goes to the smallest
-// object before IOS 16, but to the top-left object in IOS 16.
-// Overrides this method to focus the first eligiable semantics object in hit test order.
+// iOS uses this method to determine the hittest results when users touch
+// explore in VoiceOver.
+//
+// For overlapping UIAccessibilityElements (e.g. a stack) in IOS, the focus
+// goes to the smallest object before IOS 16, but to the top-left object in
+// IOS 16. Overrides this method to focus the first eligiable semantics
+// object in hit test order.
 - (id)_accessibilityHitTest:(CGPoint)point withEvent:(UIEvent*)event {
   return [self search:point];
 }
 
+// iOS calls this method when this item is swipe-to-focusd in VoiceOver.
+- (BOOL)accessibilityScrollToVisible {
+  [self showOnScreen];
+  return YES;
+}
+
+// iOS calls this method when this item is swipe-to-focusd in VoiceOver.
+- (BOOL)accessibilityScrollToVisibleWithChild:(id)child {
+  if ([child isKindOfClass:[SemanticsObject class]]) {
+    [child showOnScreen];
+    return YES;
+  }
+  return NO;
+}
+
 - (NSAttributedString*)accessibilityAttributedLabel {
   NSString* label = [self accessibilityLabel];
   if (label.length == 0) {
@@ -750,7 +772,7 @@ - (void)accessibilityElementDidBecomeFocused {
   [self bridge]->AccessibilityObjectDidBecomeFocused([self uid]);
   if ([self node].HasFlag(flutter::SemanticsFlags::kIsHidden) ||
       [self node].HasFlag(flutter::SemanticsFlags::kIsHeader)) {
-    [self bridge]->DispatchSemanticsAction([self uid], flutter::SemanticsAction::kShowOnScreen);
+    [self showOnScreen];
   }
   if ([self node].HasAction(flutter::SemanticsAction::kDidGainAccessibilityFocus)) {
     [self bridge]->DispatchSemanticsAction([self uid],

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

@@ -93,7 +93,8 @@ @interface SemanticsObjectTest : XCTestCase
 @end
 
 @interface SemanticsObject (Tests)
-
+- (BOOL)accessibilityScrollToVisible;
+- (BOOL)accessibilityScrollToVisibleWithChild:(id)child;
 - (id)_accessibilityHitTest:(CGPoint)point withEvent:(UIEvent*)event;
 @end
 
@@ -202,6 +203,42 @@ - (void)testAccessibilityHitTestNoFocusableItem {
   XCTAssertNil(hitTestResult);
 }
 
+- (void)testAccessibilityScrollToVisible {
+  fml::WeakPtrFactory<flutter::MockAccessibilityBridge> factory(
+      new flutter::MockAccessibilityBridge());
+  fml::WeakPtr<flutter::MockAccessibilityBridge> bridge = factory.GetWeakPtr();
+  SemanticsObject* object3 = [[SemanticsObject alloc] initWithBridge:bridge uid:3];
+
+  flutter::SemanticsNode node3;
+  node3.id = 3;
+  node3.rect = SkRect::MakeXYWH(0, 0, 200, 200);
+  [object3 setSemanticsNode:&node3];
+
+  [object3 accessibilityScrollToVisible];
+
+  XCTAssertTrue(bridge->observations.size() == 1);
+  XCTAssertTrue(bridge->observations[0].id == 3);
+  XCTAssertTrue(bridge->observations[0].action == flutter::SemanticsAction::kShowOnScreen);
+}
+
+- (void)testAccessibilityScrollToVisibleWithChild {
+  fml::WeakPtrFactory<flutter::MockAccessibilityBridge> factory(
+      new flutter::MockAccessibilityBridge());
+  fml::WeakPtr<flutter::MockAccessibilityBridge> bridge = factory.GetWeakPtr();
+  SemanticsObject* object3 = [[SemanticsObject alloc] initWithBridge:bridge uid:3];
+
+  flutter::SemanticsNode node3;
+  node3.id = 3;
+  node3.rect = SkRect::MakeXYWH(0, 0, 200, 200);
+  [object3 setSemanticsNode:&node3];
+
+  [object3 accessibilityScrollToVisibleWithChild:object3];
+
+  XCTAssertTrue(bridge->observations.size() == 1);
+  XCTAssertTrue(bridge->observations[0].id == 3);
+  XCTAssertTrue(bridge->observations[0].action == flutter::SemanticsAction::kShowOnScreen);
+}
+
 - (void)testAccessibilityHitTestOutOfRect {
   fml::WeakPtrFactory<flutter::AccessibilityBridgeIos> factory(
       new flutter::MockAccessibilityBridge());