UILabel最后没有动画

Question

我有一个UITextField数组和2个UIButtons，我可以添加或删除一个。当我单击按钮时，使用方法UIView.animated（）动画动画，并且其下的标签也可以，但是当我删除了最后一个textField，标签没有动画。我用gif来弄明白我的意思。

这是代码：

let lastItem = newRecipeModel.textField[index]

        newRecipeModel.textField.remove(at: index)

        UIView.animate(withDuration: 1, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 1, options: .curveEaseOut, animations: {

            lastItem.alpha = 0

            if index>0{
                self.newRecipeView.directives.topAnchor.constraint(equalTo: self.newRecipeModel.textField[index-1].bottomAnchor, constant: 15).isActive = true
                self.newRecipeView.directives.leftAnchor.constraint(equalTo: self.newRecipeView.ingredientsTextField.leftAnchor).isActive = true
            }else if index == 0{
                self.newRecipeView.directives.topAnchor.constraint(equalTo: self.newRecipeView.ingredientsTextField.bottomAnchor, constant: 15).isActive = true
                self.newRecipeView.directives.leftAnchor.constraint(equalTo: self.newRecipeView.ingredientsTextField.leftAnchor).isActive = true
            }

            self.view.layoutIfNeeded()

            }, completion: { (true) in

                lastItem.removeFromSuperview()
                self.view.layoutIfNeeded()
        })