iOS Animate height constraint issue

Question

I have a problem with the animation of a view after changing it's height constraint. In the screenshot, you can see it's initial value of 120.0. The animation works but the constraint update from my second view (the blue one) happens directly and not during the animation. This means that second view jumps to the top directly. With the following code, I will animate the change of the height constraint:

UIView.animate(withDuration: 3.0, animations: {
    self.heightConstraint?.constant = 0.0
    self.myLabel.alpha = 0.0
    self.layoutIfNeeded()
})

Does anybody know why?

Set the constraint outside of the animation block and just call `layoutIfNeeded` in the animation block. — Paulw11, Jul 10 '17 at 10:53
This don't work. I experience the same behaviour. I need to say, that my two views are also in a scroll view. Can this be the reason? — Marco Schließer, Jul 10 '17 at 11:04
So i found the error. The problem is, that i subclassed the view and did the animation stuff there. So i need to call self.superview?.layoutIfNeeded() instead of self.layoutIfNeeded() — Marco Schließer, Jul 10 '17 at 11:10
Possible duplicate of [How do I animate constraint changes?](https://stackoverflow.com/questions/12622424/how-do-i-animate-constraint-changes) — Bhautik Ziniya, Jul 10 '17 at 12:44

score 3 · Answer 1 · edited Jul 11 '17 at 01:16

3

self.heightConstraint?.constant = 0.0
self.myLabel.alpha = 0.0
UIView.animate(withDuration: 3.0, animations: {
    self.layoutIfNeeded()
})

It should be like this.

edited Jul 11 '17 at 01:16

Pang

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answered Jul 10 '17 at 10:55

Payal

31
2

score 1 · Answer 2 · answered Jul 10 '17 at 10:54

1

For animating constraint changes, you need to write code like below to work.

self.heightConstraint?.constant = 0.0
self.myLabel.alpha = 0.0

UIView.animate(withDuration: 5) {
    self.layoutIfNeeded()
}

answered Jul 10 '17 at 10:54

Sivajee Battina

4,124
2
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45

1

No, you don't need to. – FreeNickname Jul 10 '17 at 11:20

score 1 · Answer 3 · answered Jul 10 '17 at 12:30

You need to call self.layoutIfNeeded() before and after updating constraint constant. Change your code to :

self.layoutIfNeeded()

UIView.animate(withDuration: 3.0, animations: {
    self.heightConstraint?.constant = 0.0
    self.myLabel.alpha = 0.0
    self.layoutIfNeeded()
})

iOS Animate height constraint issue

3 Answers3