Add ObjC Turbo Module Event Emitter example (#44914)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/44914

Shows a proof of concept how '*strongly typed Turbo Module scoped*' `EventEmitters` can be used in a ObjC Turbo Module.

## Changelog:

[iOS] [Added] - Add ObjC Turbo Module Event Emitter example

Reviewed By: rshest

Differential Revision: D57650830

fbshipit-source-id: c5c2dee4766484e9e58415e33c084999a9ae3bc6

packages/react-native/ReactCommon/react/nativemodule/core/platform/ios/ReactCommon/RCTTurboModule.h

@@ -7,8 +7,6 @@
 
 #pragma once
 
-#import <memory>
-
 #import <Foundation/Foundation.h>
 
 #import <React/RCTBridge.h>
@@ -16,6 +14,9 @@
 #import <React/RCTModuleMethod.h>
 #import <ReactCommon/CallInvoker.h>
 #import <ReactCommon/TurboModule.h>
+#import <react/bridging/bridging.h>
+#import <functional>
+#import <memory>
 #import <string>
 #import <unordered_map>
 
@@ -27,12 +28,21 @@ namespace facebook::react {
 
 class CallbackWrapper;
 class Instance;
+using EventEmitterCallback = std::function<void(const std::string &, id)>;
 
 namespace TurboModuleConvertUtils {
 jsi::Value convertObjCObjectToJSIValue(jsi::Runtime &runtime, id value);
 id convertJSIValueToObjCObject(jsi::Runtime &runtime, const jsi::Value &value, std::shared_ptr<CallInvoker> jsInvoker);
 } // namespace TurboModuleConvertUtils
 
+template <>
+struct Bridging<id> {
+  static jsi::Value toJs(jsi::Runtime &rt, const id &value)
+  {
+    return TurboModuleConvertUtils::convertObjCObjectToJSIValue(rt, value);
+  }
+};
+
 /**
  * ObjC++ specific TurboModule base class.
  */
@@ -64,6 +74,8 @@ class JSI_EXPORT ObjCTurboModule : public TurboModule {
  protected:
   void setMethodArgConversionSelector(NSString *methodName, size_t argIndex, NSString *fnName);
 
+  void setEventEmitterCallback(EventEmitterCallback eventEmitterCallback);
+
   /**
    * Why is this virtual?
    *
@@ -154,9 +166,17 @@ class JSI_EXPORT ObjCTurboModule : public TurboModule {
 
 } // namespace facebook::react
 
+@interface EventEmitterCallbackWrapper : NSObject {
+ @public
+  facebook::react::EventEmitterCallback _eventEmitterCallback;
+}
+@end
+
 @protocol RCTTurboModule <NSObject>
 - (std::shared_ptr<facebook::react::TurboModule>)getTurboModule:
     (const facebook::react::ObjCTurboModule::InitParams &)params;
+@optional
+- (void)setEventEmitterCallback:(EventEmitterCallbackWrapper *)eventEmitterCallbackWrapper;
 @end
 
 /**

packages/react-native/ReactCommon/react/nativemodule/core/platform/ios/ReactCommon/RCTTurboModule.mm

@@ -813,5 +813,18 @@ void ObjCTurboModule::setMethodArgConversionSelector(NSString *methodName, size_
   methodArgConversionSelectors_[methodName][argIndex] = selectorValue;
 }
 
+void ObjCTurboModule::setEventEmitterCallback(EventEmitterCallback eventEmitterCallback)
+{
+  if ([instance_ conformsToProtocol:@protocol(RCTTurboModule)] &&
+      [instance_ respondsToSelector:@selector(setEventEmitterCallback:)]) {
+    EventEmitterCallbackWrapper *wrapper = [EventEmitterCallbackWrapper new];
+    wrapper->_eventEmitterCallback = std::move(eventEmitterCallback);
+    [(id<RCTTurboModule>)instance_ setEventEmitterCallback:wrapper];
+  }
+}
+
 } // namespace react
 } // namespace facebook
+
+@implementation EventEmitterCallbackWrapper
+@end

packages/react-native/ReactCommon/react/nativemodule/samples/platform/ios/ReactCommon/RCTNativeSampleTurboModuleSpec.h

@@ -43,7 +43,15 @@
 
 @end
 
-@interface NativeSampleTurboModuleSpecBase : NSObject
+@interface NativeSampleTurboModuleSpecBase : NSObject {
+ @protected
+  facebook::react::EventEmitterCallback _eventEmitterCallback;
+}
+- (void)setEventEmitterCallback:(EventEmitterCallbackWrapper *_Nonnull)eventEmitterCallbackWrapper;
+- (void)emitOnPress;
+- (void)emitOnClick:(NSString *)value;
+- (void)emitOnChange:(NSDictionary *)value;
+- (void)emitOnSubmit:(NSArray *)value;
 @end
 
 namespace facebook::react {

packages/react-native/ReactCommon/react/nativemodule/samples/platform/ios/ReactCommon/RCTNativeSampleTurboModuleSpec.mm

@@ -224,9 +224,40 @@ NativeSampleTurboModuleSpecJSI::NativeSampleTurboModuleSpecJSI(const ObjCTurboMo
   methodMap_["getObjectAssert"] = MethodMetadata{1, __hostFunction_NativeSampleTurboModuleSpecJSI_getObjectAssert};
   methodMap_["promiseAssert"] = MethodMetadata{0, __hostFunction_NativeSampleTurboModuleSpecJSI_promiseAssert};
   methodMap_["getConstants"] = MethodMetadata{0, __hostFunction_NativeSampleTurboModuleSpecJSI_getConstants};
+  eventEmitterMap_["onPress"] = std::make_shared<AsyncEventEmitter<id>>();
+  eventEmitterMap_["onClick"] = std::make_shared<AsyncEventEmitter<id>>();
+  eventEmitterMap_["onChange"] = std::make_shared<AsyncEventEmitter<id>>();
+  eventEmitterMap_["onSubmit"] = std::make_shared<AsyncEventEmitter<id>>();
+  setEventEmitterCallback([&](const std::string &name, id value) {
+    static_cast<AsyncEventEmitter<id> &>(*eventEmitterMap_[name]).emit(value);
+  });
 }
 
 } // namespace facebook::react
 
 @implementation NativeSampleTurboModuleSpecBase
+- (void)setEventEmitterCallback:(EventEmitterCallbackWrapper *_Nonnull)eventEmitterCallbackWrapper
+{
+  _eventEmitterCallback = std::move(eventEmitterCallbackWrapper->_eventEmitterCallback);
+}
+
+- (void)emitOnPress
+{
+  _eventEmitterCallback("onPress", nil);
+}
+
+- (void)emitOnClick:(NSString *)value
+{
+  _eventEmitterCallback("onClick", value);
+}
+
+- (void)emitOnChange:(NSDictionary *)value
+{
+  _eventEmitterCallback("onChange", value);
+}
+
+- (void)emitOnSubmit:(NSArray *)value
+{
+  _eventEmitterCallback("onSubmit", value);
+}
 @end

packages/react-native/ReactCommon/react/nativemodule/samples/platform/ios/ReactCommon/RCTSampleTurboModule.mm

@@ -82,6 +82,10 @@ RCT_EXPORT_MODULE()
 RCT_EXPORT_METHOD(voidFunc)
 {
   // Nothing to do
+  [self emitOnPress];
+  [self emitOnClick:@"click"];
+  [self emitOnChange:@{@"a" : @1, @"b" : @"two"}];
+  [self emitOnSubmit:@[ @{@"a" : @1, @"b" : @"two"}, @{@"a" : @3, @"b" : @"four"} ]];
 }
 
 RCT_EXPORT_SYNCHRONOUS_TYPED_METHOD(NSNumber *, getBool : (BOOL)arg)