RCTEvent protocol changes (3/7)

Summary:
I want to use the `RCTEvent` protocol for touch events as well. That's why I'm removing not very well defined `body` property and replacing it with `arguments` method, which will return an array that will be passed directly to the js call.
I think this makes sense because there is no unified arguments format for all events and and the called  js method (`moduleDotMethod`) is already event specific.
This way touch events and scroll events can result in calling a completely different js function with a completely different arguments (what they indeed currently do).

public
___
//This diff is part of a larger stack. For high level overview what's going on jump to D2884593.//

Reviewed By: nicklockwood

Differential Revision: D2884590

fb-gh-sync-id: 2c1885c3414e255d8572c0fbbbfe62a23d94dd06

Examples/UIExplorer/UIExplorerUnitTests/RCTEventDispatcherTests.m

@@ -29,7 +29,6 @@
 
 @synthesize viewTag = _viewTag;
 @synthesize eventName = _eventName;
-@synthesize body = _body;
 
 - (instancetype)initWithViewTag:(NSNumber *)viewTag eventName:(NSString *)eventName body:(NSDictionary<NSString *, id> *)body
 {
@@ -52,6 +51,11 @@
   return @"RCTDeviceEventEmitter.emit";
 }
 
+- (NSArray *)arguments
+{
+  return @[_eventName, _body];
+}
+
 @end
 
 @interface RCTEventDispatcherTests : XCTestCase
@@ -89,7 +93,7 @@
 - (void)testLegacyEventsAreImmediatelyDispatched
 {
   [[_bridge expect] enqueueJSCall:_JSMethod
-                             args:@[_eventName, _body]];
+                             args:[_testEvent arguments]];
 
   [_eventDispatcher sendDeviceEventWithName:_eventName body:_body];
 
@@ -100,7 +104,7 @@
 {
   _testEvent.canCoalesce = NO;
   [[_bridge expect] enqueueJSCall:_JSMethod
-                             args:@[_eventName, _body]];
+                             args:[_testEvent arguments]];
 
   [_eventDispatcher sendEvent:_testEvent];
 
@@ -112,7 +116,7 @@
   [_eventDispatcher sendEvent:_testEvent];
 
   [[_bridge expect] enqueueJSCall:@"RCTDeviceEventEmitter.emit"
-                             args:@[_eventName, _body]];
+                             args:[_testEvent arguments]];
 
   [(id<RCTFrameUpdateObserver>)_eventDispatcher didUpdateFrame:nil];
 
@@ -129,7 +133,7 @@
   [_eventDispatcher sendEvent:_testEvent];
 
   [[_bridge expect] enqueueJSCall:@"RCTDeviceEventEmitter.emit"
-                             args:@[_eventName, _body]];
+                             args:[_testEvent arguments]];
 
   [(id<RCTFrameUpdateObserver>)_eventDispatcher didUpdateFrame:nil];
 
@@ -147,10 +151,10 @@
   [_eventDispatcher sendEvent:_testEvent];
 
   [[_bridge expect] enqueueJSCall:@"RCTDeviceEventEmitter.emit"
-                             args:@[firstEventName, _body]];
+                             args:[firstEvent arguments]];
 
   [[_bridge expect] enqueueJSCall:@"RCTDeviceEventEmitter.emit"
-                             args:@[_eventName, _body]];
+                             args:[_testEvent arguments]];
 
   [(id<RCTFrameUpdateObserver>)_eventDispatcher didUpdateFrame:nil];
 

React/Base/RCTEventDispatcher.h

@@ -48,12 +48,14 @@ RCT_EXTERN NSString *RCTNormalizeInputEventName(NSString *eventName);
 
 @property (nonatomic, strong, readonly) NSNumber *viewTag;
 @property (nonatomic, copy, readonly) NSString *eventName;
-@property (nonatomic, copy, readonly) NSDictionary *body;
 
 - (BOOL)canCoalesce;
 - (id<RCTEvent>)coalesceWithEvent:(id<RCTEvent>)newEvent;
 
+// used directly for doing a JS call
 + (NSString *)moduleDotMethod;
+// must contain only JSON compatible values
+- (NSArray *)arguments;
 
 @end
 

React/Base/RCTEventDispatcher.m

@@ -159,19 +159,7 @@ RCT_EXPORT_MODULE()
 
 - (void)dispatchEvent:(id<RCTEvent>)event
 {
-  NSMutableArray<id /* any JSON value */> *arguments = [NSMutableArray new];
-
-  if (event.viewTag) {
-    [arguments addObject:event.viewTag];
-  }
-
-  [arguments addObject:RCTNormalizeInputEventName(event.eventName)];
-
-  if (event.body) {
-    [arguments addObject:event.body];
-  }
-
-  [_bridge enqueueJSCall:[[event class] moduleDotMethod] args:arguments];
+  [_bridge enqueueJSCall:[[event class] moduleDotMethod] args:[event arguments]];
 }
 
 - (dispatch_queue_t)methodQueue

React/Views/RCTScrollView.m

@@ -129,6 +129,11 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
   return @"RCTEventEmitter.receiveEvent";
 }
 
+- (NSArray *)arguments
+{
+  return @[self.viewTag, RCTNormalizeInputEventName(self.eventName), [self body]];
+}
+
 @end
 
 /**