encodeOffset弃用的修订

Question

我正在尝试将此代码转换为Swift5。我收到2条错误消息：

  

'encodedOffset'已弃用：encodedOffset已弃用为   最常见的用法是不正确的。使用utf16Offset（in :)实现   相同的行为。

我该如何解决？

extension UITextView {
    func frame(ofTextRange range: Range<String.Index>?) -> CGRect? {
        guard let range = range else { return nil }
        let length = range.upperBound.encodedOffset-range.lowerBound.encodedOffset
        guard
            let start = position(from: beginningOfDocument, offset: range.lowerBound.encodedOffset),
            let end = position(from: start, offset: length),
            let txtRange = textRange(from: start, to: end)
            else { return nil }
        let rect = self.firstRect(for: txtRange)
        return self.convert(rect, to: textInputView)
    }
}