title: How to calculate the height of NSAttributedString, given width and number of lines?
body: <p>I want to display 3 lines of NSAttributedString. Is there a way to figure out the needed height, based on width and number of lines?</p>
  
  <p>And I don't want to create a UILabel to do the size calculation, since I want the calculation to be done in background thread.</p>