Programming iOS 6, 3rd Edition

Core Text

Underlying all text drawing on iOS is Core Text. Before iOS 6, Core Text was the only way to draw styled text on iOS; now that an NSAttributedString can be drawn directly, or handed to an built-in interface object for it to draw, you may have less need of Core Text. Nevertheless, Core Text can still do some things you can’t do in any other way, and it is sitting there under the hood, so you may as well be aware of it. It is implemented by the Core Text framework; to utilize it, your app must link to CoreText.framework, and your code must import <CoreText/CoreText.h>. It uses C, not Objective-C, and it’s rather verbose, but getting started with it is not difficult.

A good example of the sort of thing Core Text can do that can’t be done any other way is to convert between fonts within a font family. Under CoreText, a font is a CTFont (a CTFontRef), a type which is unfortunately not bridged to UIFont. In this example, I’ll create an attributed string using only Core Text calls. You can use an NSAttributed string or its Core Foundation counterpart, CFAttributedString; they, at least, are toll-free bridged. The Core Text attribute names are listed in Apple’s Core Text String Attributes Reference, along with their value types.

I’ll start with a mutable attributed string:

NSString* s = @"Yo ho ho and a bottle of rum!";
NSMutableAttributedString* mas =
    [[NSMutableAttributedString alloc] initWithString:s];

Now I’ll apply some attributes, using Core Text calls exclusively. I’ll cycle ...