Fabric: `FabricUIManager::dispatchEventToEmptyTarget` got coupled with `dispatchEventToTarget`

Summary:
@public
Instead of having two methods it's easier to have just one which can be abstracted as `EventPipe`.

Reviewed By: mdvacca

Differential Revision: D8886231

fbshipit-source-id: af9fd92dc4afa1219a11acce0aa021a85c94d232

ReactCommon/fabric/events/primitives.h

@@ -7,10 +7,12 @@
 
 #pragma once
 
+#include <folly/dynamic.h>
+
 namespace facebook {
 namespace react {
 
-enum class EventPriority {
+enum class EventPriority: int {
   SynchronousUnbatched,
   SynchronousBatched,
   AsynchronousUnbatched,
@@ -19,7 +21,7 @@ enum class EventPriority {
   Sync = SynchronousUnbatched,
   Work = SynchronousBatched,
   Interactive = AsynchronousUnbatched,
-  Deferred = AsynchronousBatched,
+  Deferred = AsynchronousBatched
 };
 
 /* `InstanceHandler`, `EventTarget`, and `EventHandler` are all opaque
@@ -32,5 +34,13 @@ enum class EventPriority {
 using EventTarget = struct EventTargetDummyStruct {} *;
 using EventHandler = struct EventHandlerDummyStruct {} *;
 
+/*
+ * EmptyEventTarget is used when some event cannot be dispatched to an original
+ * event target but still has to be dispatched to preserve consistency of event flow.
+ */
+static const EventTarget EmptyEventTarget = nullptr;
+
+using EventPipe = std::function<void(const EventTarget &eventTarget, const std::string &type, const folly::dynamic &payload)>;
+
 } // namespace react
 } // namespace facebook

ReactCommon/fabric/uimanager/FabricUIManager.cpp

@@ -114,21 +114,22 @@ void FabricUIManager::setReleaseEventTargetFunction(std::function<ReleaseEventTa
   releaseEventTargetFunction_ = releaseEventTargetFunction;
 }
 
-void FabricUIManager::dispatchEventToEmptyTarget(const std::string &type, const folly::dynamic &payload) const {
-  dispatchEventToEmptyTargetFunction_(
-    eventHandler_,
-    const_cast<std::string &>(type),
-    const_cast<folly::dynamic &>(payload)
-  );
-}
-
 void FabricUIManager::dispatchEventToTarget(const EventTarget &eventTarget, const std::string &type, const folly::dynamic &payload) const {
+  if (eventTarget != EmptyEventTarget) {
     dispatchEventToTargetFunction_(
       eventHandler_,
       eventTarget,
       const_cast<std::string &>(type),
       const_cast<folly::dynamic &>(payload)
     );
+  }
+  else {
+    dispatchEventToEmptyTargetFunction_(
+      eventHandler_,
+      const_cast<std::string &>(type),
+      const_cast<folly::dynamic &>(payload)
+    );
+  }
 }
 
 void FabricUIManager::releaseEventTarget(const EventTarget &eventTarget) const {

ReactCommon/fabric/uimanager/FabricUIManager.h

@@ -51,7 +51,6 @@ public:
 
 #pragma mark - Native-facing Interface
 
-  void dispatchEventToEmptyTarget(const std::string &type, const folly::dynamic &payload) const;
   void dispatchEventToTarget(const EventTarget &eventTarget, const std::string &type, const folly::dynamic &payload) const;
   void releaseEventTarget(const EventTarget &eventTarget) const;