8.5. Datasources

Simple controls like text fields and pop-up buttons work by explicitly getting and setting values. Unless you set a new string for the text field, it won’t change. Some of the more complex controls in Cocoa use a different technique: they load their data from a datasource.

In most cases, a datasource object can be a member of any class; often it’s declared as an id type. It has to implement a few key methods that the view can call to load data. In some cases, the methods are declared in a formal @protocol declaration, but sometimes they’re just included as part of a category in the view’s header file.