TouchDownPanGestureRecognizer.swift

import UIKit
import UIKit.UIGestureRecognizerSubclass

class ViewController: UIViewController {
    let flickView = UIView()
    var propertyAnimator: UIViewPropertyAnimator?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        flickView.backgroundColor = .systemOrange
        flickView.frame = CGRect(x: 0.0, y: 0.0, width: 300.0, height: view.bounds.height)
        view.addSubview(flickView)
        
        let panGestureRecognizer = CustomPanGestureRecognizer(target: self, action: #selector(panned(panGestureRecognizer:)))
        panGestureRecognizer.requiresExclusiveTouchType = true
        flickView.addGestureRecognizer(panGestureRecognizer)
    }

    @objc private func panned(panGestureRecognizer: UIPanGestureRecognizer) {
        if panGestureRecognizer.state == .began {
            NSLog("Gesture began")
            
            if let propertyAnimator {
                let label = UILabel(frame: CGRect(x: 200.0, y: 100.0, width: 300.0, height: 300.0))
                label.numberOfLines = 0
                label.text = "Communicated"
                view.addSubview(label)
                
                propertyAnimator.stopAnimation(true)
                self.propertyAnimator = nil
                panGestureRecognizer.state = .cancelled
            }
        } else if panGestureRecognizer.state == .changed {
            flickView.frame.origin.x = panGestureRecognizer.translation(in: flickView).x
        } else if panGestureRecognizer.state == .ended {
            NSLog("Gesture ended")
            
            // Yes, a linear animation here is a horrible idea 😛
            let propertyAnimator = UIViewPropertyAnimator(duration: 3.0, curve: .linear)
            self.propertyAnimator = propertyAnimator
            
            propertyAnimator.addAnimations {
                self.flickView.frame.origin.x = self.view.bounds.width - self.flickView.bounds.width
            }
            
            propertyAnimator.startAnimation()
        }
    }
}

class CustomPanGestureRecognizer: UIPanGestureRecognizer {
    var totalTouches = 0
    let label = UILabel(frame: CGRect(x: 20.0, y: 100.0, width: 300.0, height: 300.0))
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
        super.touchesBegan(touches, with: event)
        
        // Immediately change state to began, which should stop any existing animations
        self.state = .began
        
        totalTouches += 1
        
        guard totalTouches > 1 else { return }
        
        label.numberOfLines = 0
        label.text = "Touched \(totalTouches)"
        view!.superview!.addSubview(label)
    }
}