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import ExpoModulesCore
// This view will be used as a native component. Make sure to inherit from `ExpoView`
// to apply the proper styling (e.g. border radius and shadows).
class ExpoScrollForwarderView: ExpoView, UIGestureRecognizerDelegate {
var scrollViewTag: Int? {
didSet {
self.tryFindScrollView()
}
}
private var rctScrollView: RCTScrollView?
private var rctRefreshCtrl: RCTRefreshControl?
private var cancelGestureRecognizers: [UIGestureRecognizer]?
private var animTimer: Timer?
private var initialOffset: CGFloat = 0.0
private var didImpact: Bool = false
required init(appContext: AppContext? = nil) {
super.init(appContext: appContext)
let pg = UIPanGestureRecognizer(target: self, action: #selector(callOnPan(_:)))
pg.delegate = self
self.addGestureRecognizer(pg)
let tg = UITapGestureRecognizer(target: self, action: #selector(callOnPress(_:)))
tg.isEnabled = false
tg.delegate = self
let lpg = UILongPressGestureRecognizer(target: self, action: #selector(callOnPress(_:)))
lpg.minimumPressDuration = 0.01
lpg.isEnabled = false
lpg.delegate = self
self.cancelGestureRecognizers = [lpg, tg]
}
// We don't want to recognize the scroll pan gesture and the swipe back gesture together
func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
if gestureRecognizer is UIPanGestureRecognizer, otherGestureRecognizer is UIPanGestureRecognizer {
return false
}
return true
}
// We only want the "scroll" gesture to happen whenever the pan is vertical, otherwise it will
// interfere with the native swipe back gesture.
override func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
guard let gestureRecognizer = gestureRecognizer as? UIPanGestureRecognizer else {
return true
}
let velocity = gestureRecognizer.velocity(in: self)
return abs(velocity.y) > abs(velocity.x)
}
// This will be used to cancel the scroll animation whenever we tap inside of the header. We don't need another
// recognizer for this one.
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
self.stopTimer()
}
// This will be used to cancel the animation whenever we press inside of the scroll view. We don't want to change
// the scroll view gesture's delegate, so we add an additional recognizer to detect this.
@IBAction func callOnPress(_ sender: UITapGestureRecognizer) -> Void {
self.stopTimer()
}
@IBAction func callOnPan(_ sender: UIPanGestureRecognizer) -> Void {
guard let rctsv = self.rctScrollView, let sv = rctsv.scrollView else {
return
}
let translation = sender.translation(in: self).y
if sender.state == .began {
if sv.contentOffset.y < 0 {
sv.contentOffset.y = 0
}
self.initialOffset = sv.contentOffset.y
}
if sender.state == .changed {
sv.contentOffset.y = self.dampenOffset(-translation + self.initialOffset)
if sv.contentOffset.y <= -130, !didImpact {
let generator = UIImpactFeedbackGenerator(style: .light)
generator.impactOccurred()
self.didImpact = true
}
}
if sender.state == .ended {
let velocity = sender.velocity(in: self).y
self.didImpact = false
if sv.contentOffset.y <= -130 {
self.rctRefreshCtrl?.forwarderBeginRefreshing()
return
}
// A check for a velocity under 250 prevents animations from occurring when they wouldn't in a normal
// scroll view
if abs(velocity) < 250, sv.contentOffset.y >= 0 {
return
}
self.startDecayAnimation(translation, velocity)
}
}
func startDecayAnimation(_ translation: CGFloat, _ velocity: CGFloat) {
guard let sv = self.rctScrollView?.scrollView else {
return
}
var velocity = velocity
self.enableCancelGestureRecognizers()
if velocity > 0 {
velocity = min(velocity, 5000)
} else {
velocity = max(velocity, -5000)
}
var animTranslation = -translation
self.animTimer = Timer.scheduledTimer(withTimeInterval: 1.0 / 120, repeats: true) { timer in
velocity *= 0.9875
animTranslation = (-velocity / 120) + animTranslation
let nextOffset = self.dampenOffset(animTranslation + self.initialOffset)
if nextOffset <= 0 {
if self.initialOffset <= 1 {
self.scrollToOffset(0)
} else {
sv.contentOffset.y = 0
}
self.stopTimer()
return
} else {
sv.contentOffset.y = nextOffset
}
if abs(velocity) < 5 {
self.stopTimer()
}
}
}
func dampenOffset(_ offset: CGFloat) -> CGFloat {
if offset < 0 {
return offset - (offset * 0.55)
}
return offset
}
func tryFindScrollView() {
guard let scrollViewTag = scrollViewTag else {
return
}
// Before we switch to a different scrollview, we always want to remove the cancel gesture recognizer.
// Otherwise we might end up with duplicates when we switch back to that scrollview.
self.removeCancelGestureRecognizers()
self.rctScrollView = self.appContext?
.findView(withTag: scrollViewTag, ofType: RCTScrollView.self)
self.rctRefreshCtrl = self.rctScrollView?.scrollView.refreshControl as? RCTRefreshControl
self.addCancelGestureRecognizers()
}
func addCancelGestureRecognizers() {
self.cancelGestureRecognizers?.forEach { r in
self.rctScrollView?.scrollView?.addGestureRecognizer(r)
}
}
func removeCancelGestureRecognizers() {
self.cancelGestureRecognizers?.forEach { r in
self.rctScrollView?.scrollView?.removeGestureRecognizer(r)
}
}
func enableCancelGestureRecognizers() {
self.cancelGestureRecognizers?.forEach { r in
r.isEnabled = true
}
}
func disableCancelGestureRecognizers() {
self.cancelGestureRecognizers?.forEach { r in
r.isEnabled = false
}
}
func scrollToOffset(_ offset: Int, animated: Bool = true) -> Void {
self.rctScrollView?.scroll(toOffset: CGPoint(x: 0, y: offset), animated: animated)
}
func stopTimer() -> Void {
self.disableCancelGestureRecognizers()
self.animTimer?.invalidate()
self.animTimer = nil
}
}
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