Animating view on viewDidAppear not working correctly - Swift

Question

I am trying to get a view to animate from the centre of the screen, to leave the screen after 1 second when the view loads.

The problem I am having is that after a millisecond of the view being in the original (correct) position upon loading, it then snaps to the new position and animates back to the original position.

I have the following code in viewDidLoad

override func viewDidAppear(animated: Bool) {

    UIView.animateWithDuration(0.7, delay: 1, options: .CurveEaseOut, animations: {
        var loadingViewFrame = self.loadingView.frame
        loadingViewFrame.origin.y += 600

        self.loadingView.frame = loadingViewFrame
        }, completion: { finished in
            print("moved")
    })


}

I have tried putting this code in a button action and it works fine, so is there some other method I should be using when animating on viewWillAppear or is there something else I have missed?

I have removed all autolayout constraints because I read that they may cause some problems.

I also have other code in viewDidAppear as well as viewWillAppear and viewDidLoad which I could show here if you think it is useful, but I have commented out all of this code to leave with only the basic code and the same error is still occurring.

Thanks a lot for your help.

---

Edit 1

I have moved the code to viewDidLayoutSubviews and have used dispatch_once to ensure it is only done once. The image still animates from the new position to the original position, but now the image is not located in the original position for a millisecond upon loading.

This is the code I have added

    var token: dispatch_once_t = 0

override func viewDidLayoutSubviews() {
    dispatch_once(&token) {

        UIView.animateWithDuration(0.7, delay: 1, options: .CurveEaseOut, animations: {
            var loadingViewFrame = self.loadingView.frame
            loadingViewFrame.origin.x += 600

            self.loadingView.frame = loadingViewFrame
            }, completion: { finished in
                print("moved")
        })
    }
}

Answer 1

First off, you need to call super.viewDidAppear(animated) when you override viewDidAppear: in your view controller subclass.

Unfortunately, it seems to work just fine for me with this view controller so there must be something else going on...

class ViewController: UITableViewController {
    var loadingView: UIView!

    override func viewDidLoad() {
            super.viewDidLoad()

        loadingView = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
        loadingView.backgroundColor = UIColor.redColor()
        loadingView.center = view.center
        view.addSubview(loadingView)
    }

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

        UIView.animateWithDuration(0.7, delay: 1, options: .CurveEaseOut, animations: {
            var loadingViewFrame = self.loadingView.frame
            loadingViewFrame.origin.y += 600

            self.loadingView.frame = loadingViewFrame
        }, completion: nil)
    }
}

Your issue is most-likely because layoutSubviews may be called after viewDidAppear: (I believe this is different for iOS 8 vs iOS 9) so the changes you made get overridden almost immediately. You can confirm this by overriding viewDidLayoutSubviews in your UIViewController subclass and breakpointing viewDidLoad, viewWillAppear:, viewDidAppear:, and viewDidLayoutSubviews to see what order they happen in.

One thing you can do to achieve a similar effect is use a dispatch_once block with a once_token that is a property of your class to execute the animation in viewDidLayoutSubviews. This will insure that your animation is executed once per instance of your class after the initial view layout has occurred. This might be what you're looking for.

If you could provide more of your view controller code or a github link I may be able to give you a better, less potentially hacky, answer about what is going on.