在Timer中运行UIView.animate

Question

I made an application that counts down every second starting from the number 10. The countdown is animated . Here's the code:

import UIKit

class ViewController: UIViewController {

    var startNumber = 10

    lazy var numberLabel: UILabel = {
        let label = UILabel()
        label.translatesAutoresizingMaskIntoConstraints = false
        label.font = label.font.withSize(160)
        label.textColor = .lightGray
        return label
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .white

        view.addSubview(numberLabel)

        NSLayoutConstraint.activate([
            numberLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            numberLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor)
            ])

        _ = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { (time) in

            self.numberLabel.text = String(self.startNumber)
            self.startNumber -= 1

            UIView.animate(withDuration: 0.99, animations: {
                self.numberLabel.alpha = 0
            }, completion: { (true) in
                self.numberLabel.alpha = 1
            })

        }
    }

}

The countdown displays an uneven animation of numbers if both the UIView and Timer interval are equal. That's why in the code the UIView interval is set to 0.99 instead of 1 to display an animated countdown for every number. The animation still isn't smooth since you can see the numbers "flick" in a millisecond but I assume that's because the interval has been set on 0.99 instead of 1.

My questions are:

1) Why does setting an equal interval on UIView and Timer result in an odd countdown animation?

2) Does the countdown count still count down for every second or for 0.99 seconds?

Answer 1

Change the code to look like that

 _ = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { (time) in


        self.startNumber -= 1

         self.numberLabel.alpha = 1

        UIView.setAnimationCurve(UIViewAnimationCurve.easeInOut)

        UIView.animate(withDuration: 1, animations: {

            self.numberLabel.text = String(self.startNumber)
            self.numberLabel.alpha = 0
        }, completion: { (true) in

        })

    }

Answer 2

1) Why does setting an equal interval on UIView and Timer result in an odd countdown animation?

Ans: When setting equal time, the previous animation will surely overlap with the new one. So better to put a lesser time. Even less than 0.99

2) Does the countdown count still count down for every second or for 0.99 seconds?

Ans: Countdown will be triggered in each second regardless of animation timer