UITextView/UITextField:如何检查Swift中是否按下了delete键

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
    if text.isEmpty {
        // 按下了delete键
        print("按下了delete键")
    }
    return true
}

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    if string.isEmpty {
        // 按下了delete键
        print("按下了delete键")
    }
    return true
}