reintroduced coalescing key for events

Summary: This was previously removed in D2884587, but we will need it going forward. See D3092867 for reasons why it's necessary again.

Reviewed By: javache

Differential Revision: D3092848

fb-gh-sync-id: 0d10dbac4148fcc8e035d32d8eab50f876d99e88
fbshipit-source-id: 0d10dbac4148fcc8e035d32d8eab50f876d99e88

Examples/UIExplorer/UIExplorerUnitTests/RCTEventDispatcherTests.m

@@ -29,14 +29,19 @@
 
 @synthesize viewTag = _viewTag;
 @synthesize eventName = _eventName;
+@synthesize coalescingKey = _coalescingKey;
 
-- (instancetype)initWithViewTag:(NSNumber *)viewTag eventName:(NSString *)eventName body:(NSDictionary<NSString *, id> *)body
+- (instancetype)initWithViewTag:(NSNumber *)viewTag
+                      eventName:(NSString *)eventName
+                           body:(NSDictionary<NSString *, id> *)body
+                  coalescingKey:(uint16_t)coalescingKey
 {
   if (self = [super init]) {
     _viewTag = viewTag;
     _eventName = eventName;
     _body = body;
     _canCoalesce = YES;
+    _coalescingKey = coalescingKey;
   }
   return self;
 }
@@ -85,7 +90,8 @@
   _body = @{ @"foo": @"bar" };
   _testEvent = [[RCTTestEvent alloc] initWithViewTag:nil
                                            eventName:_eventName
-                                                body:_body];
+                                                body:_body
+                                       coalescingKey:0];
 
   _JSMethod = [[_testEvent class] moduleDotMethod];
 }
@@ -127,7 +133,8 @@
 {
   RCTTestEvent *nonCoalescingEvent = [[RCTTestEvent alloc] initWithViewTag:nil
                                                                  eventName:_eventName
-                                                                      body:@{}];
+                                                                      body:@{}
+                                                             coalescingKey:0];
   nonCoalescingEvent.canCoalesce = NO;
   [_eventDispatcher sendEvent:_testEvent];
 
@@ -144,7 +151,8 @@
 {
   RCTTestEvent *ignoredEvent = [[RCTTestEvent alloc] initWithViewTag:nil
                                                            eventName:_eventName
-                                                                body:@{ @"other": @"body" }];
+                                                                body:@{ @"other": @"body" }
+                                                       coalescingKey:0];
 
   [_eventDispatcher sendEvent:ignoredEvent];
   [_eventDispatcher sendEvent:_testEvent];
@@ -162,7 +170,8 @@
   NSString *firstEventName = RCTNormalizeInputEventName(@"firstEvent");
   RCTTestEvent *firstEvent = [[RCTTestEvent alloc] initWithViewTag:nil
                                                            eventName:firstEventName
-                                                                body:_body];
+                                                                body:_body
+                                                     coalescingKey:0];
 
   [_eventDispatcher sendEvent:firstEvent];
   [_eventDispatcher sendEvent:_testEvent];

React/Base/RCTEventDispatcher.h

@@ -48,6 +48,7 @@ RCT_EXTERN NSString *RCTNormalizeInputEventName(NSString *eventName);
 
 @property (nonatomic, strong, readonly) NSNumber *viewTag;
 @property (nonatomic, copy, readonly) NSString *eventName;
+@property (nonatomic, assign, readonly) uint16_t coalescingKey;
 
 - (BOOL)canCoalesce;
 - (id<RCTEvent>)coalesceWithEvent:(id<RCTEvent>)newEvent;
@@ -95,7 +96,7 @@ RCT_EXTERN NSString *RCTNormalizeInputEventName(NSString *eventName);
 
 /**
  * Send a pre-prepared event object.
- * 
+ *
  * If the event can be coalesced it is added to a pool of events that are sent at the beginning of the next js frame.
  * Otherwise if the event cannot be coalesced we first flush the pool of coalesced events and the new event after that.
  *

React/Base/RCTEventDispatcher.m

@@ -30,7 +30,9 @@ static NSNumber *RCTGetEventID(id<RCTEvent> event)
 {
   return @(
     event.viewTag.intValue |
-    (((uint64_t)event.eventName.hash & 0xFFFF) << 32));
+    (((uint64_t)event.eventName.hash & 0xFFFF) << 32) |
+    (((uint64_t)event.coalescingKey) << 48)
+  );
 }
 
 @interface RCTEventDispatcher() <RCTFrameUpdateObserver>

React/Base/RCTTouchEvent.m

@@ -18,6 +18,7 @@
 
 @synthesize eventName = _eventName;
 @synthesize viewTag = _viewTag;
+@synthesize coalescingKey = _coalescingKey;
 
 - (instancetype)initWithEventName:(NSString *)eventName
                      reactTouches:(NSArray<NSDictionary *> *)reactTouches

React/Views/RCTScrollView.m

@@ -59,6 +59,11 @@ CGFloat const ZINDEX_STICKY_HEADER = 50;
 
 RCT_NOT_IMPLEMENTED(- (instancetype)init)
 
+- (uint16_t)coalescingKey
+{
+  return 0;
+}
+
 - (NSDictionary *)body
 {
   NSDictionary *body = @{