Using Timer to determine ProgressBar value (NSProgressIndicator & UIActivityIndicator)

ProgressBarTimer.swift

@IBOutlet var progressBar: NSProgressIndicator!        // Progress Bar Object
var progressValue = 0.0                                // Progress Bar Value (Double)

override func viewDidLoad() {
    super.viewDidLoad()
    
    progressBar.doubleValue = progressValue
    startProgressLoader()
}

func startProgressLoader() {
    // The Timer closure will allow you to set a looping interval
    Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { timer in
        self.progressValue += 2.0        // 0.1 * 2.0 = 20% bar progress per second
        self.progressBar.doubleValue = self.progressValue
        
        // Once progress reaches 100%, stop the Timer with invalidate() and
        // set ProgressBar to indeterminate (or simply set .isHidden = true)
        // Remember to .stopAnimation()!
        if self.progressValue >= 100.0 {
            timer.invalidate()
            self.progressBar.isIndeterminate = true
            self.endProgressLoader()
        }
    }
}

// BONUS: Fade out ProgressBar with animation
func endProgressLoader() {
    NSAnimationContext.runAnimationGroup({ (context) -> Void in
        content.duration = 1.0        // Set animation completion time to 1 second
        progressBar.alpha = 0         // Fade out ProgressBar
    }, completionHandler: { () -> Void in
        self.progressBar.stopAnimation(self)    // Stop background animation
    )}
}