Counting up/down numbers animation

Question

I have an UIPageViewController with a number in the center of each VC in it.

I want that when I swipe from view to view, the number will begin

Answer 1

You can use NSTimer to achieve this.

Here is example project I created for you.

Create layout like this:

Then in your ViewController do like so:

import UIKit

class ViewController: UIViewController {

    @IBOutlet var countingLabel: UILabel!
    var number = 0
    var destinationNumber = 30
    var timer: NSTimer!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


    @IBAction func startButtonTapped(sender: AnyObject) {
        timer = NSTimer.scheduledTimerWithTimeInterval(0.1, target: self, selector: "countUp", userInfo: nil, repeats: true)
    }

    func countUp() {
        if number < destinationNumber {
            number += 1
            countingLabel.text = "\(number)"
        } else {
            timer.invalidate()
        }
    }
}

It will work.

Answer 2

Do not overcomplicate with timers and invalidations, etc.

extension UILabel {    
    func countAnimation(upto: Double) {
        let from: Double = text?.replace(string: ",", replacement: ".").components(separatedBy: CharacterSet.init(charactersIn: "-0123456789.").inverted).first.flatMap { Double($0) } ?? 0.0
        let steps: Int = 20
        let duration = 0.350
        let delay = duration / Double(steps)
        let diff = upto - from
        for i in 0...steps {
            DispatchQueue.main.asyncAfter(deadline: .now() + delay * Double(i)) {
                self.text = "\(from + diff * (Double(i) / Double(delay)))"
            }
        }
    }
}