How to run a loop in ViewDidAppear in Swift? - ios

Question

I want to display a blue and black rectangle alternatively on the launch of the app. I wrote this code. Its compiling fine without any error, but there is no result.
import UIKit
class ViewController: UIViewController {
var mybool = true
override func viewDidAppear(_ animated: Bool) {
while(mybool){
let firstFrame = CGRect(x: 160, y: 240, width: 100, height: 150)
let firstView = UIView(frame: firstFrame)
firstView.backgroundColor = UIColor.blue
view.addSubview(firstView)
let secondView = UIView(frame: firstFrame)
secondView.backgroundColor = UIColor.black
view.addSubview(secondView)
}
}
}
Can anyone tell me where I am going wrong?
Thanks in advance

Answer 1

Do not run an while waiting for a property to change on the main thread, ever! It's the thread that your whole UI relies on. The app will look like it has crashed and iOS will kill it sooner or later.
Use Core Animations:
weak var loadingView: UIView!
override func viewDidLoad() {
super.viewDidLoad()
let frame = CGRect(x: 160, y: 240, width: 100, height: 150)
let subview = UIView(frame: frame)
subview.backgroundColor = .black
self.view.addSubview(subview)
UIView.animate(withDuration: 1, delay: 0, options: [.autoreverse, .repeat, .curveEaseInOut], animations: {
subview.backgroundColor = .blue
}, completion: nil)
self.loadingView = subview
}
When you want to stop the animation (for example, when loading has finished) :
func stopAnimation() {
loadingView.layer.removeAllAnimations()
}