Animate UIView宽度不起作用

Question

尝试像这样设置UIView的宽度。但它没有做任何事情。为什么？评论的部分更改了视图的alpha，并且可以正常工作。

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

我想你需要将调用与layoutIfNeeded()集成，这要求自动布局立即强制布局。