Add a11y support for embedded iOS platform view

lib/ui/semantics.dart

@@ -604,7 +604,11 @@ class SemanticsUpdateBuilder extends NativeFieldWrapperClass2 {
   /// The field `platformViewId` references the platform view, whose semantics
   /// nodes will be added as children to this node. If a platform view is
   /// specified, `childrenInHitTestOrder` and `childrenInTraversalOrder` must be
-  /// empty.
+  /// empty, and other semantic configurations will be ignored. The ignored configurations
+  /// include:[flags], [actions], [textSelectionBase], [textSelectionExtent], [scrollChildren],
+  /// [scrollIndex], [scrollPosition], [scrollExtentMax], [scrollExtentMin], [elevation],
+  /// [thickness], [label], [hint], [value], [increasedValue], [decreasedValue], [textDirection],
+  /// [transform], [childrenInTraversalOrder], [childrenInHitTestOrder], [additionalActions]
   ///
   /// For scrollable nodes `scrollPosition` describes the current scroll
   /// position in logical pixel. `scrollExtentMax` and `scrollExtentMin`

lib/ui/semantics/semantics_node.cc

@@ -7,6 +7,8 @@
 #include <string.h>
 
 namespace blink {
+
+constexpr int32_t kMinPlatfromViewId = -1;
 
 SemanticsNode::SemanticsNode() = default;
 
@@ -21,5 +23,9 @@ bool SemanticsNode::HasAction(SemanticsAction action) {
 bool SemanticsNode::HasFlag(SemanticsFlags flag) {
   return (flags & static_cast<int32_t>(flag)) != 0;
 }
+
+    bool SemanticsNode::IsPlatformViewNode() {
+        return platformViewId > kMinPlatfromViewId;
+    }
 
 }  // namespace blink

lib/ui/semantics/semantics_node.h

@@ -80,6 +80,9 @@ struct SemanticsNode {
 
   bool HasAction(SemanticsAction action);
   bool HasFlag(SemanticsFlags flag);
+
+  // Weather this node is for embeded platform views.
+  bool IsPlatformViewNode();
 
   int32_t id = 0;
   int32_t flags = 0;

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

@@ -165,6 +165,13 @@
   composition_order_.push_back(view_id);
 }
 
+NSObject<FlutterPlatformView>* FlutterPlatformViewsController::GetPlatformViewByID(int view_id) {
+  if (views_.empty()) {
+    return nil;
+  }
+  return views_[view_id].get();
+}
+
 std::vector<SkCanvas*> FlutterPlatformViewsController::GetCurrentCanvases() {
   std::vector<SkCanvas*> canvases;
   for (size_t i = 0; i < composition_order_.size(); i++) {

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

@@ -58,6 +58,13 @@ class FlutterPlatformViewsController {
 
   void PrerollCompositeEmbeddedView(int view_id);
 
+  // Returns the FlutterPlatformView object associated with the view_id.
+  //
+  // If the FlutterPlatformViewsController does not contain any FlutterPlatformView object or
+  // a FlutterPlatformView object asscociated with the view_id cannot be found, the method returns
+  // nil.
+  NSObject<FlutterPlatformView>* GetPlatformViewByID(int view_id);
+
   std::vector<SkCanvas*> GetCurrentCanvases();
 
   SkCanvas* CompositeEmbeddedView(int view_id, const flow::EmbeddedViewParams& params);

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

@@ -113,7 +113,9 @@ class PlatformViewIOS;
 
 class AccessibilityBridge final {
  public:
-  AccessibilityBridge(UIView* view, PlatformViewIOS* platform_view);
+  AccessibilityBridge(UIView* view,
+                      PlatformViewIOS* platform_view,
+                      FlutterPlatformViewsController* platform_views_controller);
   ~AccessibilityBridge();
 
   void UpdateSemantics(blink::SemanticsNodeUpdates nodes,
@@ -129,6 +131,10 @@ class AccessibilityBridge final {
 
   fml::WeakPtr<AccessibilityBridge> GetWeakPtr();
 
+  FlutterPlatformViewsController* GetFlutterPlatformViewsController() const {
+    return platform_views_controller_;
+  };
+
   void clearState();
 
  private:
@@ -139,6 +145,7 @@ class AccessibilityBridge final {
 
   UIView* view_;
   PlatformViewIOS* platform_view_;
+  FlutterPlatformViewsController* platform_views_controller_;
   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

@@ -11,6 +11,7 @@
 #import <UIKit/UIKit.h>
 
 #include "flutter/fml/logging.h"
+#include "flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViews_Internal.h"
 #include "flutter/shell/platform/darwin/ios/platform_view_ios.h"
 
 namespace {
@@ -163,8 +164,9 @@ - (BOOL)isAccessibilityElement {
   // entire element tree looking for such a hit.
 
   //  We enforce in the framework that no other useful semantics are merged with these nodes.
-  if ([self node].HasFlag(blink::SemanticsFlags::kScopesRoute))
+  if ([self node].HasFlag(blink::SemanticsFlags::kScopesRoute) || [self node].IsPlatformViewNode())
     return false;
+
   return ([self node].flags != 0 &&
           [self node].flags != static_cast<int32_t>(blink::SemanticsFlags::kIsHidden)) ||
          ![self node].label.empty() || ![self node].value.empty() || ![self node].hint.empty() ||
@@ -436,6 +438,21 @@ - (nullable id)accessibilityElementAtIndex:(NSInteger)index {
     return _semanticsObject;
   }
   SemanticsObject* child = [_semanticsObject children][index - 1];
+
+  // If the child is a semantic node for a platform view,
+  // inject the platform view into the iOS accessibility tree.
+  shell::FlutterPlatformViewsController* controller =
+      _bridge.get()->GetFlutterPlatformViewsController();
+  if (child.node.IsPlatformViewNode() && controller) {
+    NSObject<FlutterPlatformView>* platformViewContainer =
+        controller->GetPlatformViewByID(child.node.platformViewId);
+    UIView* platformView = [platformViewContainer view];
+    if (platformView) {
+      child.accessibilityElements = @[ platformView ];
+      return child;
+    }
+  }
+
   if ([child hasChildren])
     return [child accessibilityContainer];
   return child;
@@ -485,9 +502,12 @@ - (BOOL)accessibilityScroll:(UIAccessibilityScrollDirection)direction {
 
 namespace shell {
 
-AccessibilityBridge::AccessibilityBridge(UIView* view, PlatformViewIOS* platform_view)
+AccessibilityBridge::AccessibilityBridge(UIView* view,
+                                         PlatformViewIOS* platform_view,
+                                         FlutterPlatformViewsController* platform_views_controller)
     : view_(view),
       platform_view_(platform_view),
+      platform_views_controller_(platform_views_controller),
       objects_([[NSMutableDictionary alloc] init]),
       weak_factory_(this),
       previous_route_id_(0),
@@ -660,6 +680,14 @@ - (BOOL)accessibilityScroll:(UIAccessibilityScrollDirection)direction {
         [object.parent.children replaceObjectAtIndex:positionInChildlist withObject:object];
         objects_.get()[@(node.id)] = object;
       }
+
+      BOOL isPlatformViewNode = node.IsPlatformViewNode();
+      BOOL wasPlatformViewNode = object.node.IsPlatformViewNode();
+      if (wasPlatformViewNode && !isPlatformViewNode) {
+        // The node changed its type from platform view node to something else. In this
+        // case, we need to clean up the accessibility elements that we previously added.
+        object.accessibilityElements = nil;
+      }
     }
   }
   return object;

shell/platform/darwin/ios/platform_view_ios.mm

@@ -50,7 +50,8 @@
 
     if (accessibility_bridge_) {
       accessibility_bridge_.reset(
-          new AccessibilityBridge(static_cast<FlutterView*>(owner_controller_.get().view), this));
+          new AccessibilityBridge(static_cast<FlutterView*>(owner_controller_.get().view), this,
+                                  [owner_controller.get() platformViewsController]));
     }
     // Do not call `NotifyCreated()` here - let FlutterViewController take care
     // of that when its Viewport is sized.  If `NotifyCreated()` is called here,
@@ -96,7 +97,8 @@
   }
   if (enabled && !accessibility_bridge_) {
     accessibility_bridge_ = std::make_unique<AccessibilityBridge>(
-        static_cast<FlutterView*>(owner_controller_.get().view), this);
+        static_cast<FlutterView*>(owner_controller_.get().view), this,
+        [owner_controller_.get() platformViewsController]);
   } else if (!enabled && accessibility_bridge_) {
     accessibility_bridge_.reset();
   }