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Cocoa in a Nutshell by James Duncan Davidson, Michael Beam

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Text System Architecture

The following four classes make up the core architecture of Cocoa’s text handling system:

  • NSTextStorage is the backbone data model responsible for storing text.

  • NSTextView is responsible for presentation in the view.

  • NSLayoutManager and NSTextContainer act as controllers between the model and the view.

The relationship between these core classes is based on the same Model-View-Controller (MVC) pattern used throughout the Application Kit (and discussed in Chapter 3). Figure 5-2 shows the division of responsibilities in these four classes using the MVC pattern.

How the four core text system classes relate to one another in the MVC pattern
Figure 5-2. How the four core text system classes relate to one another in the MVC pattern

Figure 5-2 shows the relationship between the four classes, but doesn’t show the one-to-many relationship that may exist between instances of these classes. Instances of NSTextStorage own and manage one or more NSLayoutManager objects. Similarly, each instance of NSLayoutManager owns one or more NSTextContainer objects, while each text container object is paired with an NSTextView object. The nature of these relationships is what gives Cocoa’s text handling system much of its flexibility and power.

NSTextView

NSTextView represents the view, or presentation, layer of the text system; it is the class that facilitates user interaction with the text system. User interaction consists of displaying text onscreen and ...

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