Animate UIView width does not work

Question

Try to animate the width of a UIView like this. But it does not do anything. Why? The commented part changes alpha of the view, and that works.

UIView.animate(withDuration: 1, delay: 0, options: [.curveEaseInOut], animations: {

    self.constraintLookupWidth.constant = 300
    self.viewLookup.setNeedsLayout()
    //self.viewLookup.alpha = 0.2

}, completion: {complete in

    self.constraintLookupWidth.constant = 200
    self.viewLookup.setNeedsLayout()
    //self.viewLookup.alpha = 1.0
})

Answer 1

我猜您需要将调用与layoutIfNeeded()集成在一起，这会要求自动布局立即强制布局。