why is my gestureRecognizer returning nil? - swift

Question

I have tried to combine numerous tutorials to try and make a gesture recognizer start an animation on a tableView once a gesture is received on a mapView (shrinking table once map is moved like the old uber app). The animation functions, however once the animation is finished i am receiving "unexpectedly found nil when unwrapping an optional" - however it seems like it should not be nil, obviously it is, i just dont understand how. The error is 3/4 the way down, ive tried to reduce as much code as possible so parts are missing. My guess is that i have created 2 gesture recognizers which is causing the issue, but i am unsure how to combine them. Here is the code:
class RestaurantsVC: UIViewController, MKMapViewDelegate, CLLocationManagerDelegate, UIGestureRecognizerDelegate {
var animator: UIViewPropertyAnimator?
var currentState: AnimationState!
var thumbnailFrame: CGRect!
var panGestureRecognizer: UIPanGestureRecognizer!
override func viewDidLoad() {
super.viewDidLoad()
let panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(RestaurantsVC.handlePan(gestureRecognizer:)))
panGestureRecognizer.delegate = self
self.mapView.addGestureRecognizer(panGestureRecognizer)
}
func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
return true
}
#objc func handlePan (gestureRecognizer: UIPanGestureRecognizer) {
let translation = gestureRecognizer.translation(in: self.view.superview)
switch gestureRecognizer.state {
case .began:
startPanning()
animator?.startAnimation()
case .ended:
let velocity = gestureRecognizer.velocity(in: self.view.superview)
endAnimation(translation: translation, velocity: velocity)
default:
print("Something went wrong handlePan")
}
}
func startPanning() {
var finalFrame:CGRect = CGRect()
switch currentState {
// code
}
animator = UIViewPropertyAnimator(duration: 1, dampingRatio: 0.8, animations: {
})
}
func endAnimation (translation:CGPoint, velocity:CGPoint) {
if let animator = self.animator {
self.panGestureRecognizer.isEnabled = false //(this line is where i get the error)//
switch self.currentState {
case .thumbnail:
animator.isReversed = false
animator.addCompletion({ _ in
self.currentState = .minimized
self.panGestureRecognizer.isEnabled = true
})
case .minimized:
animator.isReversed = true
animator.addCompletion({ _ in
self.currentState = .thumbnail
self.panGestureRecognizer.isEnabled = true
})
default:
print("unknown state")
}
}
}
}

Answer 1

It's nil because you're never actually assigning it.
In your viewDidLoad() function, you're actually redefining a local variable which shadows the instance variable:
let panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(RestaurantsVC.handlePan(gestureRecognizer:)))
^ The 'let' keyword is redefining this variable at the local scope
You should remove the let declaration, and instead assign this as:
self.panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(RestaurantsVC.handlePan(gestureRecognizer:)))

Answer 2

This could work still without storing a reference to the gesture recognizer. You could pass the values from the gesture recognizer passed into handlePan into startAnimation and endAnimation. This would reduce the need to have superfluous properties on your class