[ReactNative] Implement proper event coalescing

React/Base/RCTBridge.h

@@ -95,6 +95,11 @@ static const char *__rct_import_##module##_##method##__ = #module"."#method;
 /**
  * The event dispatcher is a wrapper around -enqueueJSCall:args: that provides a
  * higher-level interface for sending UI events such as touches and text input.
+ *
+ * NOTE: RCTEventDispatcher is now a bridge module, this is implemented as a
+ * category but remains declared in the bridge to avoid breaking changes
+ *
+ * To be moved.
  */
 @property (nonatomic, readonly) RCTEventDispatcher *eventDispatcher;
 

React/Base/RCTBridge.m

@@ -18,7 +18,6 @@
 
 #import "RCTContextExecutor.h"
 #import "RCTConvert.h"
-#import "RCTEventDispatcher.h"
 #import "RCTJavaScriptLoader.h"
 #import "RCTKeyCommands.h"
 #import "RCTLog.h"
@@ -211,7 +210,6 @@ static NSArray *RCTBridgeModuleClassesByModuleID(void)
 
 @property (nonatomic, strong) RCTBatchedBridge *batchedBridge;
 @property (nonatomic, strong) RCTBridgeModuleProviderBlock moduleProvider;
-@property (nonatomic, strong, readwrite) RCTEventDispatcher *eventDispatcher;
 
 - (void)_invokeAndProcessModule:(NSString *)module
                          method:(NSString *)method
@@ -875,11 +873,6 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
   return _batchedBridge.modules;
 }
 
-- (RCTEventDispatcher *)eventDispatcher
-{
-  return _eventDispatcher ?: _batchedBridge.eventDispatcher;
-}
-
 #define RCT_INNER_BRIDGE_ONLY(...) \
 - (void)__VA_ARGS__ \
 { \
@@ -943,11 +936,6 @@ RCT_INNER_BRIDGE_ONLY(_invokeAndProcessModule:(NSString *)module method:(NSStrin
     _javaScriptExecutor = RCTCreateExecutor(executorClass);
     _latestJSExecutor = _javaScriptExecutor;
 
-    /**
-     * Setup event dispatcher before initializing modules to allow init calls
-     */
-    self.eventDispatcher = [[RCTEventDispatcher alloc] initWithBridge:self];
-
     /**
      * Initialize and register bridge modules *before* adding the display link
      * so we don't have threading issues

React/Base/RCTEventDispatcher.h

@@ -9,7 +9,7 @@
 
 #import <UIKit/UIKit.h>
 
-@class RCTBridge;
+#import "RCTBridge.h"
 
 typedef NS_ENUM(NSInteger, RCTTextEventType) {
   RCTTextEventTypeFocus,
@@ -28,14 +28,36 @@ typedef NS_ENUM(NSInteger, RCTScrollEventType) {
   RCTScrollEventTypeEndAnimation,
 };
 
+@protocol RCTEvent <NSObject>
+
+@required
+
+@property (nonatomic, strong, readonly) NSNumber *viewTag;
+@property (nonatomic, copy, readonly) NSString *eventName;
+@property (nonatomic, copy, readonly) NSDictionary *body;
+@property (nonatomic, assign, readonly) uint16_t coalescingKey;
+
+- (BOOL)canCoalesce;
+- (id<RCTEvent>)coalesceWithEvent:(id<RCTEvent>)newEvent;
+
++ (NSString *)moduleDotMethod;
+
+@end
+
+@interface RCTBaseEvent : NSObject <RCTEvent>
+
+- (instancetype)initWithViewTag:(NSNumber *)viewTag
+                      eventName:(NSString *)eventName
+                           body:(NSDictionary *)body NS_DESIGNATED_INITIALIZER;
+
+@end
+
 /**
  * This class wraps the -[RCTBridge enqueueJSCall:args:] method, and
  * provides some convenience methods for generating event calls.
  */
 @interface RCTEventDispatcher : NSObject
 
-- (instancetype)initWithBridge:(RCTBridge *)bridge;
-
 /**
  * Send an application-specific event that does not relate to a specific
  * view, e.g. a navigation or data update notification.
@@ -61,13 +83,6 @@ typedef NS_ENUM(NSInteger, RCTScrollEventType) {
                      reactTag:(NSNumber *)reactTag
                          text:(NSString *)text;
 
-/**
- * Send a scroll event.
- * (You can send a fake scroll event by passing nil for scrollView).
- */
-- (void)sendScrollEventWithType:(RCTScrollEventType)type
-                       reactTag:(NSNumber *)reactTag
-                     scrollView:(UIScrollView *)scrollView
-                       userData:(NSDictionary *)userData;
+- (void)sendEvent:(id<RCTEvent>)event;
 
 @end

React/Base/RCTEventDispatcher.m

@@ -11,16 +11,76 @@
 
 #import "RCTAssert.h"
 #import "RCTBridge.h"
+#import "RCTSparseArray.h"
+
+static uint64_t RCTGetEventID(id<RCTEvent> event)
+{
+  return (
+    [event.viewTag intValue] |
+    (((uint64_t)event.eventName.hash & 0xFFFF) << 32)  |
+    (((uint64_t)event.coalescingKey) << 48)
+  );
+}
+
+@implementation RCTBaseEvent
+
+@synthesize viewTag = _viewTag;
+@synthesize eventName = _eventName;
+@synthesize body = _body;
+
+- (instancetype)initWithViewTag:(NSNumber *)viewTag
+                      eventName:(NSString *)eventName
+                           body:(NSDictionary *)body
+{
+  if ((self = [super init])) {
+    _viewTag = viewTag;
+    _eventName = eventName;
+    _body = body;
+  }
+  return self;
+}
+
+- (uint16_t)coalescingKey
+{
+  return 0;
+}
+
+- (BOOL)canCoalesce
+{
+  return YES;
+}
+
+- (id<RCTEvent>)coalesceWithEvent:(id<RCTEvent>)newEvent
+{
+  return newEvent;
+}
+
++ (NSString *)moduleDotMethod
+{
+  return nil;
+}
+
+@end
+
+@interface RCTEventDispatcher() <RCTBridgeModule, RCTFrameUpdateObserver>
+
+@end
 
 @implementation RCTEventDispatcher
 {
-  RCTBridge __weak *_bridge;
+  RCTSparseArray *_eventQueue;
+  NSLock *_eventQueueLock;
 }
 
-- (instancetype)initWithBridge:(RCTBridge *)bridge
+@synthesize bridge = _bridge;
+
+RCT_EXPORT_MODULE()
+
+- (instancetype)init
 {
   if ((self = [super init])) {
-    _bridge = bridge;
+    _eventQueue = [[RCTSparseArray alloc] init];
+    _eventQueueLock = [[NSLock alloc] init];
   }
   return self;
 }
@@ -70,58 +130,71 @@ RCT_IMPORT_METHOD(RCTEventEmitter, receiveEvent);
   }];
 }
 
-/**
- * TODO: throttling
- * NOTE: the old system used a per-scrollview throttling
- * which would be fairly easy to re-implement if needed,
- * but this is non-optimal as it leads to degradation in
- * scroll responsiveness. A better solution would be to
- * coalesce multiple scroll events into a single batch.
- */
-- (void)sendScrollEventWithType:(RCTScrollEventType)type
-                       reactTag:(NSNumber *)reactTag
-                     scrollView:(UIScrollView *)scrollView
-                       userData:(NSDictionary *)userData
+- (void)sendEvent:(id<RCTEvent>)event
 {
-  static NSString *events[] = {
-    @"topScrollBeginDrag",
-    @"topScroll",
-    @"topScrollEndDrag",
-    @"topMomentumScrollBegin",
-    @"topMomentumScrollEnd",
-    @"topScrollAnimationEnd",
-  };
-
-  NSDictionary *body = @{
-    @"contentOffset": @{
-      @"x": @(scrollView.contentOffset.x),
-      @"y": @(scrollView.contentOffset.y)
-    },
-    @"contentInset": @{
-      @"top": @(scrollView.contentInset.top),
-      @"left": @(scrollView.contentInset.left),
-      @"bottom": @(scrollView.contentInset.bottom),
-      @"right": @(scrollView.contentInset.right)
-    },
-    @"contentSize": @{
-      @"width": @(scrollView.contentSize.width),
-      @"height": @(scrollView.contentSize.height)
-    },
-    @"layoutMeasurement": @{
-      @"width": @(scrollView.frame.size.width),
-      @"height": @(scrollView.frame.size.height)
-    },
-    @"zoomScale": @(scrollView.zoomScale ?: 1),
-    @"target": reactTag
-  };
-
-  if (userData) {
-    NSMutableDictionary *mutableBody = [body mutableCopy];
-    [mutableBody addEntriesFromDictionary:userData];
-    body = mutableBody;
+  if (!event.canCoalesce) {
+    [self dispatchEvent:event];
+    return;
   }
 
-  [self sendInputEventWithName:events[type] body:body];
+  [_eventQueueLock lock];
+
+  uint64_t eventID = RCTGetEventID(event);
+  id<RCTEvent> previousEvent = _eventQueue[eventID];
+
+  if (previousEvent) {
+    event = [previousEvent coalesceWithEvent:event];
+  }
+
+  _eventQueue[eventID] = event;
+
+  [_eventQueueLock unlock];
+}
+
+- (void)dispatchEvent:(id<RCTEvent>)event
+{
+  NSMutableArray *arguments = [[NSMutableArray alloc] init];
+
+  if (event.viewTag) {
+    [arguments addObject:event.viewTag];
+  }
+
+  [arguments addObject:event.eventName];
+
+  if (event.body) {
+    [arguments addObject:event.body];
+  }
+
+  [_bridge enqueueJSCall:[[event class] moduleDotMethod]
+                    args:arguments];
+}
+
+- (dispatch_queue_t)methodQueue
+{
+  return RCTJSThread;
+}
+
+- (void)didUpdateFrame:(RCTFrameUpdate *)update
+{
+  RCTSparseArray *eventQueue;
+
+  [_eventQueueLock lock];
+  eventQueue = _eventQueue;
+  _eventQueue = [[RCTSparseArray alloc] init];
+  [_eventQueueLock unlock];
+
+  for (id<RCTEvent> event in eventQueue.allObjects) {
+    [self dispatchEvent:event];
+  }
+}
+
+@end
+
+@implementation RCTBridge (RCTEventDispatcher)
+
+- (RCTEventDispatcher *)eventDispatcher
+{
+  return self.modules[RCTBridgeModuleNameForClass([RCTEventDispatcher class])];
 }
 
 @end

React/Views/RCTNavigator.m

@@ -15,6 +15,7 @@
 #import "RCTEventDispatcher.h"
 #import "RCTLog.h"
 #import "RCTNavItem.h"
+#import "RCTScrollView.h"
 #import "RCTUtils.h"
 #import "RCTView.h"
 #import "RCTWrapperViewController.h"

React/Views/RCTScrollView.h

@@ -10,13 +10,12 @@
 #import <UIKit/UIScrollView.h>
 
 #import "RCTAutoInsetsProtocol.h"
+#import "RCTEventDispatcher.h"
 #import "RCTScrollableProtocol.h"
 #import "RCTView.h"
 
 @protocol UIScrollViewDelegate;
 
-@class RCTEventDispatcher;
-
 @interface RCTScrollView : RCTView <UIScrollViewDelegate, RCTScrollableProtocol, RCTAutoInsetsProtocol>
 
 - (instancetype)initWithEventDispatcher:(RCTEventDispatcher *)eventDispatcher NS_DESIGNATED_INITIALIZER;
@@ -48,3 +47,16 @@
 @property (nonatomic, copy) NSIndexSet *stickyHeaderIndices;
 
 @end
+
+@interface RCTEventDispatcher (RCTScrollView)
+
+/**
+ * Send a scroll event.
+ * (You can send a fake scroll event by passing nil for scrollView).
+ */
+- (void)sendScrollEventWithType:(RCTScrollEventType)type
+                       reactTag:(NSNumber *)reactTag
+                     scrollView:(UIScrollView *)scrollView
+                       userData:(NSDictionary *)userData;
+
+@end

React/Views/RCTScrollView.m

@@ -21,6 +21,107 @@
 CGFloat const ZINDEX_DEFAULT = 0;
 CGFloat const ZINDEX_STICKY_HEADER = 50;
 
+@interface RCTScrollEvent : NSObject <RCTEvent>
+
+- (instancetype)initWithType:(RCTScrollEventType)type
+                    reactTag:(NSNumber *)reactTag
+                  scrollView:(UIScrollView *)scrollView
+                    userData:(NSDictionary *)userData NS_DESIGNATED_INITIALIZER;
+
+@end
+
+@implementation RCTScrollEvent
+{
+  RCTScrollEventType _type;
+  UIScrollView *_scrollView;
+  NSDictionary *_userData;
+}
+
+@synthesize viewTag = _viewTag;
+
+- (instancetype)initWithType:(RCTScrollEventType)type
+                    reactTag:(NSNumber *)reactTag
+                  scrollView:(UIScrollView *)scrollView
+                    userData:(NSDictionary *)userData
+{
+  if (self = [super init]) {
+    _type = type;
+    _viewTag = reactTag;
+    _scrollView = scrollView;
+    _userData = userData;
+  }
+  return self;
+}
+
+- (uint16_t)coalescingKey
+{
+  return 0;
+}
+
+- (NSDictionary *)body
+{
+  NSDictionary *body = @{
+    @"contentOffset": @{
+      @"x": @(_scrollView.contentOffset.x),
+      @"y": @(_scrollView.contentOffset.y)
+    },
+    @"contentInset": @{
+      @"top": @(_scrollView.contentInset.top),
+      @"left": @(_scrollView.contentInset.left),
+      @"bottom": @(_scrollView.contentInset.bottom),
+      @"right": @(_scrollView.contentInset.right)
+    },
+    @"contentSize": @{
+      @"width": @(_scrollView.contentSize.width),
+      @"height": @(_scrollView.contentSize.height)
+    },
+    @"layoutMeasurement": @{
+      @"width": @(_scrollView.frame.size.width),
+      @"height": @(_scrollView.frame.size.height)
+    },
+    @"zoomScale": @(_scrollView.zoomScale ?: 1),
+  };
+
+  if (_userData) {
+    NSMutableDictionary *mutableBody = [body mutableCopy];
+    [mutableBody addEntriesFromDictionary:_userData];
+    body = mutableBody;
+  }
+
+  return body;
+}
+
+- (NSString *)eventName
+{
+  static NSString *events[] = {
+    @"topScrollBeginDrag",
+    @"topScroll",
+    @"topScrollEndDrag",
+    @"topMomentumScrollBegin",
+    @"topMomentumScrollEnd",
+    @"topScrollAnimationEnd",
+  };
+
+  return events[_type];
+}
+
+- (BOOL)canCoalesce
+{
+  return YES;
+}
+
+- (id<RCTEvent>)coalesceWithEvent:(id<RCTEvent>)newEvent
+{
+  return newEvent;
+}
+
++ (NSString *)moduleDotMethod
+{
+  return @"RCTEventEmitter.receiveEvent";
+}
+
+@end
+
 /**
  * Include a custom scroll view subclass because we want to limit certain
  * default UIKit behaviors such as textFields automatically scrolling
@@ -442,6 +543,7 @@ RCT_SCROLL_EVENT_HANDLER(scrollViewDidZoom, RCTScrollEventTypeMove)
                                      reactTag:self.reactTag
                                    scrollView:scrollView
                                      userData:userData];
+
     // Update dispatch time
     _lastScrollDispatchTime = now;
     _allowNextScrollNoMatterWhat = NO;
@@ -630,3 +732,19 @@ RCT_SET_AND_PRESERVE_OFFSET(setScrollIndicatorInsets, UIEdgeInsets);
 }
 
 @end
+
+@implementation RCTEventDispatcher (RCTScrollView)
+
+- (void)sendScrollEventWithType:(RCTScrollEventType)type
+                       reactTag:(NSNumber *)reactTag
+                     scrollView:(UIScrollView *)scrollView
+                       userData:(NSDictionary *)userData
+{
+  RCTScrollEvent *scrollEvent = [[RCTScrollEvent alloc] initWithType:type
+                                                            reactTag:reactTag
+                                                          scrollView:scrollView
+                                                            userData:userData];
+  [self sendEvent:scrollEvent];
+}
+
+@end