title: How to estimate the proper height of a UITextField, to hold text of given font size
body: <p>I want to display a single-line text field using UITextField and I need to know before displaying it, the proper size for its containing UICollectionViewCell. The text can be one of multiple font sizes and I need to get the right height for displaying it comfortably.</p>
  
  <p>Since the text is not known in advance (it can be edited by the user), I can't use <code>NSAttributedString</code>'s <code>-size</code> and <code>-boundingRectWithSize:options:context:</code> with anything but dummy text, in which case I can't really trust the resulting size to hold any piece of text, right?</p>
  
  <p>I guess my question is: Is there a rule of thumb about typography in general, or some useful API I'm not aware of, that would allow me to determine that for displaying text at <code>X</code> pt, I need a text field with a height of <code>Y</code> px.</p>