UITextView Height Calculation

UITextView+HeightCalculation.swift

extension UITextView {
    // Note: This will trigger a text rendering!
    func calculateViewHeightWithCurrentWidth() -> CGFloat {
        let textWidth = self.frame.width -
            self.textContainerInset.left -
            self.textContainerInset.right -
            self.textContainer.lineFragmentPadding * 2.0 -
            self.contentInset.left -
            self.contentInset.right
        
        let maxSize = CGSize(width: textWidth, height: CGFloat.max)
        var calculatedSize = self.attributedText.boundingRectWithSize(maxSize,
                                                                      options: [.UsesLineFragmentOrigin, .UsesFontLeading],
                                                                      context: nil).size
        calculatedSize.height += self.textContainerInset.top
        calculatedSize.height += self.textContainerInset.bottom
        
        return ceil(calculatedSize.height)
    }
}

I made a couple of changes for my own purposes, in case it's useful for anyone else:

1. updated to fix renamed methods
2. added ability to pass in your own width. For me, this made it easier to integrate into a sizeThatFits method
3. if there is no text yet, measures with placeholder text so you get an accurate starting frame.

Thanks for getting this started!

extension UITextView {

    func neededHeightWithWidth(_ width: CGFloat) -> CGFloat {
        let textWidth = self.frame.width -
        self.textContainerInset.left -
        self.textContainerInset.right -
        self.textContainer.lineFragmentPadding * 2.0 -
        self.contentInset.left -
        self.contentInset.right
        
        let maxSize = CGSize(width: textWidth, height: CGFloat.greatestFiniteMagnitude)
        
        let attributedText: NSAttributedString
        if let text = self.attributedText, text.length > 0 {
            attributedText = text
        }
        else {
            attributedText = NSAttributedString(string: "XXX", attributes: typingAttributes)
        }
        
        var calculatedSize = attributedText.boundingRect(with: maxSize,
                                                              options: [.usesLineFragmentOrigin, .usesFontLeading],
                                                                      context: nil).size
        calculatedSize.height += self.textContainerInset.top
        calculatedSize.height += self.textContainerInset.bottom
        
        return ceil(calculatedSize.height)
    }
}