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];