Presented ViewController ignores UIView animation

Question

I have a simple animation that moves a slide up and down repeatedly. Here is the code:

    CGRect frm_down = slider.frame;
    frm_down.origin.y += 50;

    [UIView animateWithDuration:0.7
                          delay:0.0
                        options:UIViewAnimationOptionAutoreverse | UIViewAnimationOptionRepeat
                     animations:^{
                         slider.frame = frm_down;
                     }
                     completion:NULL];

This is pretty straight forward and works great; however, when I am presenting the view (self presentViewController:animated:) the animation does not happen.

In fact, the slider is INSTANTLY moved to the lower position (as if it called the animation only once and moved it back down, but not back up).

I have also tried this:

CGRect frm_down = [[[slider layer] presentationLayer] frame]

This will keep the slider in its original position instead of moving down once, and the animation still does not happen.

Any idea what I am missing? Thanks!

Answer 1

Your animation works. I tested it.

What you need is:

Instead of using:

self presentViewController:animated:

Use this:

[self addChildViewController:<YOUR_VIEWCONTROLLER>];
[self.view addSubview:<YOUR_VIEWCONTROLER>.view];
[<YOUR_VIEWCONTROLER> didMoveToParentViewController:self];

Addendum:

In your view controller's viewDidAppear, add the following code:

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    CGRect frm_down = self.view.frame;
    frm_down.origin.y += 50;

    [UIView animateWithDuration:0.7
                          delay:0.0
                        options:UIViewAnimationOptionAutoreverse | UIViewAnimationOptionRepeat
                     animations:^{
                         self.view.frame = frm_down;
                     }
                     completion:NULL];

}

It will animate when it comes into view.

I ran it as a test a priori. Hope it helps.

Answer 2

On Swift :

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

    var from_down =  self.view.frame
    from_down.origin.y += 50

    UIView.animate(withDuration: 0.2, delay: 0.0, options: .autoreverse, animations: {
        self.view.frame = from_down
        }, completion: nil)
}