Most Applications Can Use the Cocoa Text System

If your application needs to display text, and especially if its users need to enter and edit text, then you should use the Cocoa text system. The Cocoa text system is one of two text-handling systems in OS X. The other is Core Text, which provides low-level, basic text layout and font-handling capabilities to higher-level engines such as the AppKit.

Typographical Concepts Are Essential for Understanding the Text System

The Cocoa text system encodes characters as Unicode values. It translates characters into glyphs, including ligatures and other contextual forms, and handles typefaces, styles, fonts, and families. The system does text layout, placing glyphs horizontally or vertically in either direction, using font metric information, and uses kerning when appropriate. It performs high-quality line breaking and hyphenation to create lines of text with proper alignment or justification.

The Text System Comprises Views, Controllers, and Storage Classes

The Cocoa text system is abstracted as a set of classes that represent modular, layered functional areas reflecting the Model-View-Controller design paradigm. The top layer of the system is the user-interface layer of various views, the bottom layer stores the data models, and the middle layer consists of controllers that interpret keyboard input and arrange text for display.

The four primary text system classes—NSTextView, NSLayoutManager, NSTextContainer, and NSTextStorage—can be configured in various ways to accomplish different text-handling goals.

Attributes Characterize Text and Documents

The Cocoa text system handles five kinds of attributes: character attributes, such as font and size; temporary attributes used during processing or display, such as underlining of misspelled words; paragraph attributes, such as alignment and tab stops; glyph attributes that may control special handling of particular glyphs; and document attributes, such as margins and paper size.

Font Objects, the Font Panel, and the Font Manager Provide Typeface Handling

The Font panel, also called the Fonts window, is a user interface object that displays a list of available font families and styles, letting the user preview them and change the font used to display text. Text views work with NSFontPanel and NSFontManager objects to implement the font-handling system. You can create font objects using the NSFont class and query them for font metrics and detailed glyph layout information.

Text Objects Are Key to Text Editing

Usually, text editing is performed by direct user action with a text view, but it can also be accomplished by programmatic interaction with a text storage object. The text input system translates keyboard events into commands and text input. You can customize editing behavior using many methods of text system objects, through the powerful Cocoa mechanisms of notification and delegation, or, in extreme cases, by replacing the text view itself with a custom subclass.