iOS 在UITextView中查找某个Range所在的Rect

代码如下(Swift 4)：

extension UITextView {

    /// 查找文本范围所在的矩形范围
    ///
    /// - Parameter range: 文本范围
    /// - Returns: 文本范围所在的矩形范围
    func rect(forStringRange range: NSRange) -> CGRect? {

        guard let start = self.position(from: self.beginningOfDocument, offset: range.location) else { return nil }
        guard let end = self.position(from: start, offset: range.length) else { return nil }
        guard let textRange = self.textRange(from: start, to: end) else { return nil }
        let rect = self.firstRect(for: textRange)
        return self.convert(rect, from: self.textInputView)
    }

}