Drawing text into your app’s interface is one of the most complex and powerful things that iOS does for you. Fortunately, iOS also shields you from much of that complexity. All you need is some text to draw, and possibly an interface object to draw it for you.
Text to appear in your app’s interface will be an NSString (bridged from Swift String) or an NSAttributedString. NSAttributedString adds text styling to an NSString, including runs of different character styles, along with paragraph-level features such as alignment, line spacing, and margins.
To make your NSString or NSAttributedString appear in the interface, you can draw it into a graphics context, or hand it to an interface object that knows how to draw it:
Both NSString and NSAttributedString have methods (supplied by the NSStringDrawing category) for drawing themselves into any graphics context.
Interface objects that know how to draw an NSString or NSAttributedString are:
Displays text, possibly consisting of multiple lines; neither scrollable nor editable.
Displays a single line of user-editable text; may have a border, a background image, and overlay views at its right and left end.
Displays scrollable multiline text, possibly user-editable.
Deep under the hood, all text drawing is performed through a low-level technology with a C API called Core Text. Before iOS 7, certain powerful and useful text-drawing ...