[zeyap]

Summary:
Problem: With C++ Native Animated enabled on iOS, native-driven Animated.event mappings no longer receive events that libraries deliver through RCTEventDispatcher observers. The legacy ObjC Native Animated module observed them; C++ Native Animated only reads Fabric event payloads (event dispatched with eventEmitter->dispatchEvent(name, folly::dynamic)), and codegen'd component events are not readable from C++.

As a result, in some of react-navigation (oss library) examples, Gesture- and pager-driven animations (swipe-back in a JS stack navigator, tab indicators driven by a pager's onPageScroll) stop tracking user input.

Proposed change: When C++ Native Animated is enabled, RCTInstance observes its RCTEventDispatcher and hands each component event, on the main thread, to an EventEmitterListenerContainer it publishes in the context container under RCTEventDispatcherListeners. On Apple platforms, NativeAnimatedNodesManagerProvider::getOrCreate() adds its event listener to that container when present, next to its Fabric event listener.

An alternative is to let the library migrate to EventEmitter::dispatchEvent; however that way the event is also delivered to JS. In android and RNCXX, we also maintain 2 paths to intercept js dispatchEvent and platform-only event.

Changes:

• iOS (RCTInstance, new RCTEventDispatcherEventPayload): registers as an RCTEventDispatcherObserver only when cxxNativeAnimatedEnabled() is on, and forwards only component events (RCTEventEmitter.receiveEvent). The payload reads values from the event body on demand, so events no listener reads are not converted; it is never dispatched to JS.
• C++ (NativeAnimatedNodesManagerProvider, __APPLE__ only): subscribes to RCTEventDispatcherListeners from the UIManager's context container. Covers the platform-driven and shared animation backend setups, and apps that create their own provider.
• C++: EventEmitterListener.h moves from react/renderer/animated to react/renderer/core (the runtime only needs core); react/renderer/animated/EventEmitterListener.h forwards to it for existing includers.

No public API changes.

Found while auditing cxxNativeAnimatedEnabled against OSS react-navigation (7.x) and its peers react-native-gesture-handler, react-native-pager-view and react-native-screens.

Changelog:
[iOS][Fixed] - Native-driven Animated.event mappings receive events delivered through RCTEventDispatcher observers when C++ Native Animated is enabled

Differential Revision: D129152896

[meta-codesync]

@zeyap has exported this pull request. If you are a Meta employee, you can view the originating Diff in D129152896.