Swift-仅对特定约束进行动画处理

Question

I'm trying to animate constraints in my ViewController. In order to do that, I added this line to my code: I'm just trying to change the height of a UIView() (from 0 to 100)

barHeight.constant = CGFloat(100)
UIView.animate(withDuration: 2) {self.view.layoutIfNeeded()}

The problem is that, with that line, all of the constraints are animated, and it's not what I would like.

Do you know how I could animate only specific constraints and not others?

Answer 1

Call layoutSubviews before you edit the constraint you want to animate. This will cause any pending layout updates to be applied without any animation and then you can change the next constraint with animation.

Like so:

 self.view.layoutSubviews()
 barHeight.constant = CGFloat(100)
 UIView.animate(withDuration: 2) {self.view.layoutIfNeeded()}