react-native/React/Base/RCTTouchHandler.m

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */

#import "RCTTouchHandler.h"

#import <UIKit/UIGestureRecognizerSubclass.h>

#import "RCTAssert.h"
#import "RCTBridge.h"
#import "RCTLog.h"
#import "RCTUIManager.h"
#import "RCTUtils.h"
#import "UIView+React.h"

// TODO: this class behaves a lot like a module, and could be implemented as a
// module if we were to assume that modules and RootViews had a 1:1 relationship
@implementation RCTTouchHandler
{
  __weak RCTBridge *_bridge;
  BOOL _dispatchedInitialTouches;

  /**
   * Arrays managed in parallel tracking native touch object along with the
   * native view that was touched, and the React touch data dictionary.
   * This must be kept track of because `UIKit` destroys the touch targets
   * if touches are canceled and we have no other way to recover this information.
   */
  NSMutableOrderedSet *_nativeTouches;
  NSMutableArray *_reactTouches;
  NSMutableArray *_touchViews;

  BOOL _recordingInteractionTiming;
  CFTimeInterval _mostRecentEnqueueJS;
}

- (instancetype)initWithBridge:(RCTBridge *)bridge
{
  RCTAssertParam(bridge);

  if ((self = [super initWithTarget:self action:@selector(handleGestureUpdate:)])) {

    _bridge = bridge;
    _dispatchedInitialTouches = NO;
    _nativeTouches = [[NSMutableOrderedSet alloc] init];
    _reactTouches = [[NSMutableArray alloc] init];
    _touchViews = [[NSMutableArray alloc] init];

    // `cancelsTouchesInView` is needed in order to be used as a top level
    // event delegated recognizer. Otherwise, lower-level components not built
    // using RCT, will fail to recognize gestures.
    self.cancelsTouchesInView = NO;
  }
  return self;
}

RCT_NOT_IMPLEMENTED(-initWithTarget:(id)target action:(SEL)action)

typedef NS_ENUM(NSInteger, RCTTouchEventType) {
  RCTTouchEventTypeStart,
  RCTTouchEventTypeMove,
  RCTTouchEventTypeEnd,
  RCTTouchEventTypeCancel
};

#pragma mark - Bookkeeping for touch indices

- (void)_recordNewTouches:(NSSet *)touches
{
  for (UITouch *touch in touches) {

    RCTAssert(![_nativeTouches containsObject:touch],
              @"Touch is already recorded. This is a critical bug.");

    // Find closest React-managed touchable view
    UIView *targetView = touch.view;
    while (targetView) {
      if (targetView.reactTag && targetView.userInteractionEnabled &&
          [targetView reactRespondsToTouch:touch]) {
        break;
      }
      targetView = targetView.superview;
    }

    NSNumber *reactTag = [targetView reactTagAtPoint:[touch locationInView:targetView]];
    if (!reactTag || !targetView.userInteractionEnabled) {
      return;
    }

    // Get new, unique touch identifier for the react touch
    const NSUInteger RCTMaxTouches = 11; // This is the maximum supported by iDevices
    NSInteger touchID = ([_reactTouches.lastObject[@"identifier"] integerValue] + 1) % RCTMaxTouches;
    for (NSDictionary *reactTouch in _reactTouches) {
      NSInteger usedID = [reactTouch[@"identifier"] integerValue];
      if (usedID == touchID) {
        // ID has already been used, try next value
        touchID ++;
      } else if (usedID > touchID) {
        // If usedID > touchID, touchID must be unique, so we can stop looking
        break;
      }
    }

    // Create touch
    NSMutableDictionary *reactTouch = [[NSMutableDictionary alloc] initWithCapacity:9];
    reactTouch[@"target"] = reactTag;
    reactTouch[@"identifier"] = @(touchID);
    reactTouch[@"touches"] = (id)kCFNull;        // We hijack this touchObj to serve both as an event
    reactTouch[@"changedTouches"] = (id)kCFNull; // and as a Touch object, so making this JIT friendly.

    // Add to arrays
    [_touchViews addObject:targetView];
    [_nativeTouches addObject:touch];
    [_reactTouches addObject:reactTouch];
  }
}

- (void)_recordRemovedTouches:(NSSet *)touches
{
  for (UITouch *touch in touches) {
    NSUInteger index = [_nativeTouches indexOfObject:touch];
    if(index == NSNotFound) {
      continue;
    }

    [_touchViews removeObjectAtIndex:index];
    [_nativeTouches removeObjectAtIndex:index];
    [_reactTouches removeObjectAtIndex:index];
  }
}

- (void)_updateReactTouchAtIndex:(NSInteger)touchIndex
{
  UITouch *nativeTouch = _nativeTouches[touchIndex];
  CGPoint windowLocation = [nativeTouch locationInView:nativeTouch.window];
  CGPoint rootViewLocation = [nativeTouch.window convertPoint:windowLocation toView:self.view];

  UIView *touchView = _touchViews[touchIndex];
  CGPoint touchViewLocation = [nativeTouch.window convertPoint:windowLocation toView:touchView];

  NSMutableDictionary *reactTouch = _reactTouches[touchIndex];
  reactTouch[@"pageX"] = @(rootViewLocation.x);
  reactTouch[@"pageY"] = @(rootViewLocation.y);
  reactTouch[@"locationX"] = @(touchViewLocation.x);
  reactTouch[@"locationY"] = @(touchViewLocation.y);
  reactTouch[@"timestamp"] =  @(nativeTouch.timestamp * 1000); // in ms, for JS
}

/**
 * Constructs information about touch events to send across the serialized
 * boundary. This data should be compliant with W3C `Touch` objects. This data
 * alone isn't sufficient to construct W3C `Event` objects. To construct that,
 * there must be a simple receiver on the other side of the bridge that
 * organizes the touch objects into `Event`s.
 *
 * We send the data as an array of `Touch`es, the type of action
 * (start/end/move/cancel) and the indices that represent "changed" `Touch`es
 * from that array.
 */
- (void)_updateAndDispatchTouches:(NSSet *)touches
                        eventName:(NSString *)eventName
                  originatingTime:(__unused CFTimeInterval)originatingTime
{
  // Update touches
  NSMutableArray *changedIndexes = [[NSMutableArray alloc] init];
  for (UITouch *touch in touches) {
    NSInteger index = [_nativeTouches indexOfObject:touch];
    if (index == NSNotFound) {
      continue;
    }

    [self _updateReactTouchAtIndex:index];
    [changedIndexes addObject:@(index)];
  }

  if (changedIndexes.count == 0) {
    return;
  }

  // Deep copy the touches because they will be accessed from another thread
  // TODO: would it be safer to do this in the bridge or executor, rather than trusting caller?
  NSMutableArray *reactTouches = [[NSMutableArray alloc] initWithCapacity:_reactTouches.count];
  for (NSDictionary *touch in _reactTouches) {
    [reactTouches addObject:[touch copy]];
  }

  [_bridge enqueueJSCall:@"RCTEventEmitter.receiveTouches"
                    args:@[eventName, reactTouches, changedIndexes]];
}

#pragma mark - Gesture Recognizer Delegate Callbacks

static BOOL RCTAllTouchesAreCancelledOrEnded(NSSet *touches)
{
  for (UITouch *touch in touches) {
    if (touch.phase == UITouchPhaseBegan ||
        touch.phase == UITouchPhaseMoved ||
        touch.phase == UITouchPhaseStationary) {
      return NO;
    }
  }
  return YES;
}

static BOOL RCTAnyTouchesChanged(NSSet *touches)
{
  for (UITouch *touch in touches) {
    if (touch.phase == UITouchPhaseBegan ||
        touch.phase == UITouchPhaseMoved) {
      return YES;
    }
  }
  return NO;
}

- (void)handleGestureUpdate:(UIGestureRecognizer *)gesture {
  // If the gesture just recognized, send all the touches over to JS as if they just began
  if (self.state == UIGestureRecognizerStateBegan) {
    [self _updateAndDispatchTouches:[_nativeTouches set] eventName:@"topTouchStart" originatingTime:0];

    // We store this flag separately from `state` because after a gesture is recognized, its `state` changes immediately but its action (that is, this method) isn't fired until dependent gesture recognizers have failed. We only want to send move/end/cancel touch updates if we've sent the touchStart events.
    _dispatchedInitialTouches = YES;
  }
  // For the other states, we could dispatch the updates here but since we specifically send info about which touches changed, it's simpler to dispatch the updates from the raw touch methods below.
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
  [super touchesBegan:touches withEvent:event];

  // "start" has to record new touches before extracting the event.
  // "end"/"cancel" needs to remove the touch *after* extracting the event.
  [self _recordNewTouches:touches];
  if (_dispatchedInitialTouches) {
    [self _updateAndDispatchTouches:touches eventName:@"topTouchStart" originatingTime:event.timestamp];
    self.state = UIGestureRecognizerStateChanged;
  } else {
    self.state = UIGestureRecognizerStateBegan;
  }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
  [super touchesMoved:touches withEvent:event];

  if (_dispatchedInitialTouches) {
    [self _updateAndDispatchTouches:touches eventName:@"topTouchMove" originatingTime:event.timestamp];
    self.state = UIGestureRecognizerStateChanged;
  }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
  [super touchesEnded:touches withEvent:event];

  if (_dispatchedInitialTouches) {
    [self _updateAndDispatchTouches:touches eventName:@"topTouchEnd" originatingTime:event.timestamp];

    if (RCTAllTouchesAreCancelledOrEnded(event.allTouches)) {
      self.state = UIGestureRecognizerStateEnded;
    } else if (RCTAnyTouchesChanged(event.allTouches)) {
      self.state = UIGestureRecognizerStateChanged;
    }
  }
  [self _recordRemovedTouches:touches];
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
  [super touchesCancelled:touches withEvent:event];

  if (_dispatchedInitialTouches) {
    [self _updateAndDispatchTouches:touches eventName:@"topTouchCancel" originatingTime:event.timestamp];

    if (RCTAllTouchesAreCancelledOrEnded(event.allTouches)) {
      self.state = UIGestureRecognizerStateCancelled;
    } else if (RCTAnyTouchesChanged(event.allTouches)) {
      self.state = UIGestureRecognizerStateChanged;
    }
  }
  [self _recordRemovedTouches:touches];
}

- (BOOL)canPreventGestureRecognizer:(__unused UIGestureRecognizer *)preventedGestureRecognizer
{
  return NO;
}

- (BOOL)canBePreventedByGestureRecognizer:(__unused UIGestureRecognizer *)preventingGestureRecognizer
{
  return NO;
}

- (void)reset {
  _dispatchedInitialTouches = NO;
}

@end