Number of lines in UILabel in self-sizing tableview cell

I have a custom UITableViewCell subclass that is using self-sizing cells. The sizing of the cells is perfect and the label is being extended correctly. However, at run time I am trying to calculate the number of lines that the label will be extended to (I need to display the line numbers next to the label), and I am not able to achieve this. I have tried the following two methods and neither seem to be returning the correct number of lines that I am seeing when the app runs:

func lineCountForText(string: String, label: UILabel) -> Int {

        let font: UIFont = UIFont(name: "SourceCodePro-Regular", size: label.font.pointSize)!

        let rect = string.boundingRectWithSize(CGSizeMake(label.frame.width, CGFloat(MAXFLOAT)), options: NSStringDrawingOptions.UsesLineFragmentOrigin, attributes: [font : NSFontAttributeName], context: nil)

        return Int(ceil(rect.size.height/font.lineHeight))

    }

    func numberOfLinesForString(string: String, size: CGSize, font: UIFont) -> Int {
        let textStorage = NSTextStorage(string: string, attributes: [NSFontAttributeName: font])

        let textContainer = NSTextContainer(size: size)
        textContainer.lineBreakMode = .ByWordWrapping
        textContainer.maximumNumberOfLines = 0
        textContainer.lineFragmentPadding = 0

        let layoutManager = NSLayoutManager()
        layoutManager.textStorage = textStorage
        layoutManager.addTextContainer(textContainer)

        var numberOfLines = 0
        var index = 0
        var lineRange : NSRange = NSMakeRange(0, 0)
        for (; index < layoutManager.numberOfGlyphs; numberOfLines++) {
            layoutManager.lineFragmentRectForGlyphAtIndex(index, effectiveRange: &lineRange)
            index = NSMaxRange(lineRange)
        }

        return numberOfLines
    }

Am I not able to do this because it is a self-sizing cell?