在eventFirstResponder或resignFirstResponder的情况下，将对象保持在键盘顶部？

I currently have a UITextField on top of a keyboard. When you tap it, it should stick on top of the keyboard and move up smoothly. I don't know the exact duration and animation type of the keyboard, so it's really bumpy. Here's what I have:I currently have a UITextField on top of a keyb