UISearchBar显示了CancelButton动画完成

Question

我需要知道在调用

后UISearchBar的取消按钮何时完成动画

searchBar.setShowsCancelButton(false, animated: true)

我试过这个

UIView.animateWithDuration(3, animations: {
    self.searchBarView.searchBar.showsCancelButton = false
         }, completion: {finished in
         print(finished)
})

但完成块立即被触发，任何解决方案都将受到赞赏