iOS implementation of sendAccessibilityEvent

Summary:
This is the iOS native implementation of sendAccessibilityEvent for Fabric.

Changelog: [Internal]

Reviewed By: shergin

Differential Revision: D25857401

fbshipit-source-id: e57d2e7fd45052bcf05cee7d0cb6c55ee974f358

React/Fabric/Mounting/RCTMountingManager.h

@@ -38,6 +38,12 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (void)dispatchCommand:(ReactTag)reactTag commandName:(NSString *)commandName args:(NSArray *)args;
 
+/**
+ * Dispatch an accessibility event to be performed on the main thread.
+ * Can be called from any thread.
+ */
+- (void)sendAccessibilityEvent:(ReactTag)reactTag eventType:(NSString *)eventType;
+
 - (void)synchronouslyUpdateViewOnUIThread:(ReactTag)reactTag
                              changedProps:(NSDictionary *)props
                       componentDescriptor:(const facebook::react::ComponentDescriptor &)componentDescriptor;

React/Fabric/Mounting/RCTMountingManager.mm

@@ -180,6 +180,22 @@ static void RCTPerformMountInstructions(
   });
 }
 
+- (void)sendAccessibilityEvent:(ReactTag)reactTag eventType:(NSString *)eventType
+{
+  if (RCTIsMainQueue()) {
+    // Already on the proper thread, so:
+    // * No need to do a thread jump;
+    // * No need to allocate a block.
+    [self synchronouslyDispatchAccessbilityEventOnUIThread:reactTag eventType:eventType];
+    return;
+  }
+
+  RCTExecuteOnMainQueue(^{
+    RCTAssertMainQueue();
+    [self synchronouslyDispatchAccessbilityEventOnUIThread:reactTag eventType:eventType];
+  });
+}
+
 - (void)initiateTransaction:(MountingCoordinator::Shared const &)mountingCoordinator
 {
   SystraceSection s("-[RCTMountingManager initiateTransaction:]");
@@ -257,4 +273,12 @@ static void RCTPerformMountInstructions(
   [componentView handleCommand:commandName args:args];
 }
 
+- (void)synchronouslyDispatchAccessbilityEventOnUIThread:(ReactTag)reactTag eventType:(NSString *)eventType
+{
+  if ([@"focus" isEqualToString:eventType]) {
+    UIView<RCTComponentViewProtocol> *componentView = [_componentViewRegistry findComponentViewWithTag:reactTag];
+    UIAccessibilityPostNotification(UIAccessibilityLayoutChangedNotification, componentView);
+  }
+}
+
 @end

React/Fabric/RCTScheduler.h

@@ -31,6 +31,9 @@ NS_ASSUME_NONNULL_BEGIN
                         commandName:(std::string const &)commandName
                                args:(folly::dynamic const)args;
 
+- (void)schedulerDidSendAccessibilityEvent:(facebook::react::ShadowView const &)shadowView
+                                 eventType:(std::string const &)eventType;
+
 @end
 
 /**

React/Fabric/RCTScheduler.mm

@@ -59,6 +59,12 @@ class SchedulerDelegateProxy : public SchedulerDelegate {
     // Does nothing for now.
   }
 
+  void schedulerDidSendAccessibilityEvent(const ShadowView &shadowView, std::string const &eventType) override
+  {
+    RCTScheduler *scheduler = (__bridge RCTScheduler *)scheduler_;
+    [scheduler.delegate schedulerDidSendAccessibilityEvent:shadowView eventType:eventType];
+  }
+
  private:
   void *scheduler_;
 };

React/Fabric/RCTSurfacePresenter.mm

@@ -465,6 +465,15 @@ static BackgroundExecutor RCTGetBackgroundExecutor()
   [self->_mountingManager dispatchCommand:tag commandName:commandStr args:argsArray];
 }
 
+- (void)schedulerDidSendAccessibilityEvent:(const facebook::react::ShadowView &)shadowView
+                                 eventType:(const std::string &)eventType
+{
+  ReactTag tag = shadowView.tag;
+  NSString *eventTypeStr = [[NSString alloc] initWithUTF8String:eventType.c_str()];
+
+  [self->_mountingManager sendAccessibilityEvent:tag eventType:eventTypeStr];
+}
+
 - (void)addObserver:(id<RCTSurfacePresenterObserver>)observer
 {
   std::unique_lock<better::shared_mutex> lock(_observerListMutex);