io swift Animation: alpha and constraint

Question

This is my code, and the skip button animation does not work. It just disappear immediately. It just disappear

skipButtonBottomConstraint.constant = -40

 UIView.animate(withDuration: 1.0, animations: {

                self.titleLabel.alpha = 0
                self.skipButton.alpha = 0
                self.pageControl.alpha = 0


                self.view.setNeedsLayout()
    })

could you explain me the reason?

Show all other operations/codes you have set around this function. May you have set something that effect on animation — Krunal, Nov 09 '17 at 11:26
Possible duplicate of [How do I animate constraint changes?](https://stackoverflow.com/questions/12622424/how-do-i-animate-constraint-changes) — Jack, Nov 09 '17 at 11:48
What your main design goal? Can you explain it? Also what you expected from this block? It's just disappears and not anything else. — Mannopson, Nov 09 '17 at 12:38
Also you should call it before animation block to make sure all pending operation are completed — Grzegorz Krukowski, Nov 09 '17 at 14:08

score 2 · Answer 1 · answered Nov 09 '17 at 11:30

2

I think Paul is right, and you should be calling layoutIfNeeded() inside the animation block, not setNeedsLayout()

answered Nov 09 '17 at 11:30

Duncan C

128,072
22
173
272

Grzegorz Krukowski · Answer 2 · 2017-11-09T14:05:00.010

-2

Make sure you are calling layoutIfNeeded after you setNeedsLayout

Also as Apple recommends - call it once before the animation block to ensure that all pending layout operations have been completed.

self.view.layoutIfNeeded()
self.skipButtonBottomConstraint.constant = -40
UIView.animate(withDuration: 1.0, animations: {    
        self.titleLabel.alpha = 0
        self.skipButton.alpha = 0
        self.pageControl.alpha = 0
        self.view.layoutIfNeeded()
})

edited Nov 09 '17 at 14:05

answered Nov 09 '17 at 11:21

Grzegorz Krukowski

18,081
5
50
71

nope.... don't work, it still disappear suddenly, I don't know if it's because it moves immediately out of screen or because of the alpha – Andrea Miotto Nov 09 '17 at 11:24
@TheMiotz According to code you have shown here, this answer is correct and it should work – Krunal Nov 09 '17 at 11:27
You should definitely adjust the constraint outside the animation block – Paulw11 Nov 09 '17 at 11:28

io swift Animation: alpha and constraint

2 Answers2