Swift - UIProgressView is not smooth with NSTimer

Question

So I am using an NSTimer to let the user know the app is working. The progress bar is set up to last 3 seconds, but when running, it displays in a 'ticking' motion and it is not smooth like it should be. Is there anyway I can make it more smooth - I'm sure just a calculation error on my part....

If anyone could take a look that would be great. Here is the code:

import UIKit

class LoadingScreen: UIViewController {


    var time : Float = 0.0
    var timer: NSTimer?

    @IBOutlet weak var progressView: UIProgressView!


    override func viewDidLoad() {
        super.viewDidLoad()

// Do stuff

timer = NSTimer.scheduledTimerWithTimeInterval(0.1, target: self, selector:Selector("setProgress"), userInfo: nil, repeats: true)

}//close viewDidLoad

  func setProgress() {
        time += 0.1
        progressView.progress = time / 3
        if time >= 3 {
            timer!.invalidate()
        }
    }

}

Answer 1

Edit: A simple 3 second UIView animation (Recommended)

If your bar is just moving smoothly to indicate activity, possibly consider using a UIActivityIndicatorView or a custom UIView animation:

override func viewDidAppear(animated: Bool)
{
    super.viewDidAppear(animated)

    UIView.animateWithDuration(3, animations: { () -> Void in
        self.progressView.setProgress(1.0, animated: true)
    })
}

Make sure your progressView's progress is set to zero to begin with. This will result in a smooth 3 second animation of the progress.

Simple animated progress (Works but still jumps a bit)

https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIProgressView_Class/#//apple_ref/occ/instm/UIProgressView/setProgress:animated:

func setProgress() {
    time += 0.1
    progressView.setProgress(time / 3, animated: true)
    if time >= 3 {
        timer!.invalidate()
    }
}

Option with smaller intervals. (Not recommended)

Set your timer to a smaller interval:

timer = NSTimer.scheduledTimerWithTimeInterval(0.001, target: self, selector:Selector("setProgress"), userInfo: nil, repeats: true)

Then update your function

func setProgress() {
    time += 0.001
    progressView.setProgress(time / 3, animated: true)
    if time >= 3 {
        timer!.invalidate()
    }
}

Answer 2

It's hard to say exactly what the problem is. I would like to see the output if you put a print line in setProgress to print a timestamp. Is it actually firing every tenth of a second? My guess is that it is not.

Why not? Well, the timer schedules a run loop task in the main thread to execute the code in setProgress. This task cannot run until tasks in front of it in the queue do. So if there are long running tasks happening in your main thread, your timer will fire very imprecisely. My first suggestion is that this is perhaps what is happening.

Here is an example:

1. You start a timer to do something every second.
2. Immediately after, you start a long running main thread task (for example, you try to write a ton of data to a file). This task will take five seconds to complete.
3. Your timer wants to fire after one second, but your file-writing is hogging the main thread for the next four seconds, so the timer can't fire for another four seconds.

If this is the case, then to solve the problem you would either need to move that main thread work to a background thread, or else figure out a way to do it while returning to the run loop periodically. For example, during your long running main thread operation, you can periodically call runUntilDate on your run loop to let other run loop tasks execute.

Note that you couldn't just increment the progress bar fill periodically during the long running main thread task, because the progress bar will not actually animate its fill until you return to the run loop.

Answer 3

For continues loader

timer = Timer.scheduledTimer(timeInterval: 0.001, target: self, selector: #selector(setProgress), userInfo: nil, repeats: true)

and

func setProgress() {
        time += 0.001
        downloadProgressBar.setProgress(time / 3, animated: true)
        if time >= 3 {
            self.time = 0.001
            downloadProgressBar.progress = 0
            let color = self.downloadProgressBar.progressTintColor
            self.downloadProgressBar.progressTintColor = self.downloadProgressBar.trackTintColor
            self.downloadProgressBar.trackTintColor = color
        }