Apply animation duration depending on number of lines in textview (swif3)

Question

My code here animates the textview and scrolls it down.

        UIView.animate(withDuration: 10) { // 10 seconds
        self.textView.contentOffset = CGPoint(x: 0, y: 225)
    }

The problem is that it follows the same command now matter how many lines are in the textfield. What I would like to do is have the animation follow a line ratio that determines how long the duration goes for. For example for every 3 lines in the textfield it adds 1 second in duration. So if there are a total of 21 lines in the textview the duration length is going to be 7 seconds long.

Answer 1

Try this

    // Calculate number of lines according to font
    var font = UIFont.boldSystemFont(ofSize: CGFloat(11.0))
    var size: CGSize = string.size(with: font, constrainedToSize: textView.frame.size, lineBreakMode: .wordWrap) // default mode
    var numberOfLines: Float = size.height / font.lineHeight

    // 1 sec per third line
    let duration = Int(numberOfLines / 3)

    UIView.animate(withDuration: TimeInterval(duration)) {
        self.textView.contentOffset = CGPoint(x: 0, y: 225)
    }

Or you could use an extension

extension UITextView {
    func numberOfLines() -> Int {
        let layoutManager = self.layoutManager
        let numberOfGlyphs = layoutManager.numberOfGlyphs
        var lineRange: NSRange = NSMakeRange(0, 1)
        var index = 0
        var numberOfLines = 0

        while index < numberOfGlyphs {
            layoutManager.lineFragmentRectForGlyphAtIndex(
                index, effectiveRange: &lineRange
            )
            index = NSMaxRange(lineRange)
            numberOfLines += 1
        }
        return numberOfLines
    }
}

and then calculate the duration

   // 1 sec per third line
   let duration = Int(textView.numberOfLines() / 3)


   UIView.animate(withDuration: TimeInterval(duration)) {            
         self.textView.contentOffset = CGPoint(x: 0, y: 225)
    }