如何使用返回键关闭UITextView的键盘？

override func viewDidLoad() {
    super.viewDidLoad()
    textView.delegate = self
}

func textViewShouldEndEditing(_ textView: UITextView) -> Bool {
    if textView.text.isEmpty {
        return true
    }
    return false
}

func textViewDidEndEditing(_ textView: UITextView) {
    textView.resignFirstResponder()
}