Three finger a11y scrolling for iOS (#4123)

* Three finger a11y scrolling for iOS

* review comments

* review feedback

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

@@ -127,8 +127,8 @@ class PlatformMessageResponseDarwin : public blink::PlatformMessageResponse {
 
   _orientationPreferences = UIInterfaceOrientationMaskAll;
   _statusBarStyle = UIStatusBarStyleDefault;
-  _platformView =
-      std::make_shared<shell::PlatformViewIOS>(reinterpret_cast<CAEAGLLayer*>(self.view.layer));
+  _platformView = std::make_shared<shell::PlatformViewIOS>(
+      reinterpret_cast<CAEAGLLayer*>(self.view.layer), self);
 
   _platformView->Attach(
       // First frame callback.

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

@@ -12,6 +12,7 @@
 
 #include "flutter/fml/platform/darwin/scoped_nsobject.h"
 #include "flutter/lib/ui/semantics/semantics_node.h"
+#include "flutter/shell/platform/darwin/ios/framework/Headers/FlutterChannels.h"
 #include "flutter/shell/platform/darwin/ios/framework/Source/FlutterView.h"
 #include "lib/fxl/macros.h"
 #include "third_party/skia/include/core/SkMatrix44.h"
@@ -58,10 +59,12 @@ class AccessibilityBridge final {
   void VisitObjectsRecursivelyAndRemove(SemanticsObject* object,
                                         NSMutableArray<NSNumber*>* doomed_uids);
   void ReleaseObjects(std::unordered_map<int, SemanticsObject*>& objects);
+  void HandleEvent(NSDictionary<NSString*, id>* annotatedEvent);
 
   UIView* view_;
   PlatformViewIOS* platform_view_;
   fml::scoped_nsobject<NSMutableDictionary<NSNumber*, SemanticsObject*>> objects_;
+  fml::scoped_nsprotocol<FlutterBasicMessageChannel*> accessibility_channel_;
 
   FXL_DISALLOW_COPY_AND_ASSIGN(AccessibilityBridge);
 };

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

@@ -240,8 +240,6 @@ bool GeometryComparator(SemanticsObject* a, SemanticsObject* b) {
   if (!_node.HasAction(action))
     return NO;
   _bridge->DispatchSemanticsAction(_uid, action);
-  // TODO(tvolkert): provide meaningful string (e.g. "page 2 of 5")
-  UIAccessibilityPostNotification(UIAccessibilityPageScrolledNotification, nil);
   return YES;
 }
 
@@ -320,6 +318,12 @@ bool GeometryComparator(SemanticsObject* a, SemanticsObject* b) {
              : [[_semanticsObject parent] accessibilityContainer];
 }
 
+#pragma mark - UIAccessibilityAction overrides
+
+- (BOOL)accessibilityScroll:(UIAccessibilityScrollDirection)direction {
+  return [_semanticsObject accessibilityScroll:direction];
+}
+
 @end
 
 #pragma mark - AccessibilityBridge impl
@@ -327,10 +331,19 @@ bool GeometryComparator(SemanticsObject* a, SemanticsObject* b) {
 namespace shell {
 
 AccessibilityBridge::AccessibilityBridge(UIView* view, PlatformViewIOS* platform_view)
-    : view_(view), platform_view_(platform_view), objects_([[NSMutableDictionary alloc] init]) {}
+    : view_(view), platform_view_(platform_view), objects_([[NSMutableDictionary alloc] init]) {
+  accessibility_channel_.reset([[FlutterBasicMessageChannel alloc]
+         initWithName:@"flutter/accessibility"
+      binaryMessenger:platform_view->binary_messenger()
+                codec:[FlutterStandardMessageCodec sharedInstance]]);
+  [accessibility_channel_.get() setMessageHandler:^(id message, FlutterReply reply) {
+    HandleEvent((NSDictionary*)message);
+  }];
+}
 
 AccessibilityBridge::~AccessibilityBridge() {
   view_.accessibilityElements = nil;
+  [accessibility_channel_.get() setMessageHandler:nil];
 }
 
 void AccessibilityBridge::UpdateSemantics(std::vector<blink::SemanticsNode> nodes) {
@@ -375,28 +388,10 @@ void AccessibilityBridge::UpdateSemantics(std::vector<blink::SemanticsNode> node
   NSMutableArray<NSNumber*>* doomed_uids = [NSMutableArray arrayWithArray:[objects_.get() allKeys]];
   if (root)
     VisitObjectsRecursivelyAndRemove(root, doomed_uids);
-
-  bool focused_object_doomed = false;
-  for (NSNumber* uid in doomed_uids) {
-    SemanticsObject* object = objects_.get()[uid];
-    if ([object accessibilityElementIsFocused]) {
-      focused_object_doomed = true;
-      break;
-    }
-  }
-
   [objects_ removeObjectsForKeys:doomed_uids];
 
-  if (focused_object_doomed) {
-    // Previously focused element is no longer in the tree.
-    // Passing `nil` as argument to let iOS figure out what to focus next.
-    // TODO(goderbauer): Figure out which element should be focused next and post
-    //     UIAccessibilityLayoutChangedNotification with that element instead.
-    UIAccessibilityPostNotification(UIAccessibilityScreenChangedNotification, nil);
-  } else {
-    // Passing `nil` as argument to keep focus where it is.
-    UIAccessibilityPostNotification(UIAccessibilityLayoutChangedNotification, nil);
-  }
+  // TODO(goderbauer): figure out which node to focus next.
+  UIAccessibilityPostNotification(UIAccessibilityLayoutChangedNotification, nil);
 }
 
 void AccessibilityBridge::DispatchSemanticsAction(int32_t uid, blink::SemanticsAction action) {
@@ -419,4 +414,14 @@ void AccessibilityBridge::VisitObjectsRecursivelyAndRemove(SemanticsObject* obje
     VisitObjectsRecursivelyAndRemove(child, doomed_uids);
 }
 
+void AccessibilityBridge::HandleEvent(NSDictionary<NSString*, id>* annotatedEvent) {
+  NSString* type = annotatedEvent[@"type"];
+  if ([type isEqualToString:@"scroll"]) {
+    // TODO(tvolkert): provide meaningful string (e.g. "page 2 of 5")
+    UIAccessibilityPostNotification(UIAccessibilityPageScrolledNotification, @"");
+  } else {
+    NSCAssert(NO, @"Invalid event type %@", type);
+  }
+}
+
 }  // namespace shell

shell/platform/darwin/ios/platform_view_ios.h

@@ -22,7 +22,8 @@ namespace shell {
 
 class PlatformViewIOS : public PlatformView {
  public:
-  explicit PlatformViewIOS(CALayer* layer);
+  explicit PlatformViewIOS(CALayer* layer,
+                           NSObject<FlutterBinaryMessenger>* binaryMessenger);
 
   ~PlatformViewIOS() override;
 
@@ -55,12 +56,17 @@ class PlatformViewIOS : public PlatformView {
                      const std::string& main,
                      const std::string& packages) override;
 
+  NSObject<FlutterBinaryMessenger>* binary_messenger() const {
+    return binary_messenger_;
+  }
+
  private:
   std::unique_ptr<IOSSurface> ios_surface_;
   PlatformMessageRouter platform_message_router_;
   std::unique_ptr<AccessibilityBridge> accessibility_bridge_;
   fxl::Closure firstFrameCallback_;
   fxl::WeakPtrFactory<PlatformViewIOS> weak_factory_;
+  NSObject<FlutterBinaryMessenger>* binary_messenger_;
 
   void SetupAndLoadFromSource(const std::string& assets_directory,
                               const std::string& main,

shell/platform/darwin/ios/platform_view_ios.mm

@@ -17,10 +17,11 @@
 
 namespace shell {
 
-PlatformViewIOS::PlatformViewIOS(CALayer* layer)
+PlatformViewIOS::PlatformViewIOS(CALayer* layer, NSObject<FlutterBinaryMessenger>* binaryMessenger)
     : PlatformView(std::make_unique<GPURasterizer>(std::make_unique<ProcessInfoMac>())),
       ios_surface_(IOSSurface::Create(surface_config_, layer)),
-      weak_factory_(this) {}
+      weak_factory_(this),
+      binary_messenger_(binaryMessenger) {}
 
 PlatformViewIOS::~PlatformViewIOS() = default;