cocopods导入：
import RxSwift
import RxCocoa
import RxKeyboard
声明一个常量，storyboard拖拽一个UITextView：
let disposeBag = DisposeBag()
@IBOutlet weak var enterText: UITextView!
viewDidLoad()函数里面添加以下代码：
RxKeyboard.instance.frame
.drive(onNext: { frame in
if frame.origin.y == UIScreen.main.bounds.height {
UIView.animate(withDuration: 0.4, animations: {
enterText.frame = CGRect(x: 0, y: frame.origin.y, width: frame.width, height: 120)
})
} else {
UIView.animate(withDuration: 0.4, animations: {
enterText.frame = CGRect(x: 0, y: frame.origin.y - 120, width: frame.width, height: 120)
})
}
}
})
.disposed(by: disposeBag)
