NSAttributedString

NSAttributedString objects manage character strings and associated sets of attributes (for example, font and kerning) that apply to individual characters or ranges of characters in the string. An association of characters and their attributes is called an attributed string. The cluster’s two public classes, NSAttributedString and NSMutableAttributedString, declare the programmatic interface for read-only attributed strings and modifiable attributed strings, respectively. The Foundation framework defines only the basic functionality for attributed strings; in Mac OS X, additional methods supporting RTF, graphics attributes, and drawing attributed strings are described in NSAttributedString Additions, found in the Application Kit. The Application Kit also uses a subclass of NSMutableAttributedString, called NSTextStorage, to provide the storage for the Application Kit’s extended text-handling system.

In Mac OS X, the Application Kit also uses NSParagraphStyle and its subclass NSMutableParagraphStyle to encapsulate the paragraph or ruler attributes used by the NSAttributedString classes.

An attributed string identifies attributes by name, storing a value under the name in an NSDictionary object. In Mac OS X, standard attribute keys are described in the “Constants” section of NSAttributedString Application Kit Additions Reference. You can also assign any attribute name/value pair you wish to a range of characters—it is up to your application to interpret custom attributes (see Attributed String Programming Guide). If you are using attributed strings with the Core Text framework, you can also use the attribute keys defined by that framework.

Note that the default font for NSAttributedString objects is Helvetica 12-point, which differs from the Mac OS X system font Lucida Grande, so you may wish to create the string with non-default attributes suitable for your application using, for example,initWithString:attributes:.

Be aware that isEqual: comparison among NSAttributedString objects compares for exact equality, including not only literal character-by-character string equality but also equality of all attributes, which is not likely to be achieved in the case of many attributes such as attachments, lists, and tables, for example.

iOS Note: In iOS, this class is used primarily in conjunction with the Core Text framework.