Introduction to Control and Cell Programming Topics for Cocoa

Explains the relationship between Cocoa control and cell objects.

Organization of This Document

Controls and cells implement user-interface objects, like buttons, text fields, and sliders. The control is responsible for

Displaying itself
Intercepting user events (such as a clicking a button or moving a slider)
Sending actions to other objects, usually in response to a user event (such as changing a variable’s value as a slider moves or performing a command when a button is pressed.)

A control usually delegates the first two responsibilities to cells. Splitting these responsibilities off makes it easier to create a control with many identical elements (like a spreadsheet table) or with a few different elements (like a pull-down list that lets you enter a string either in a text field or from a menu of pre-elected strings).

Here are the concepts:

About Cells and Controls gives basic information on what the NSCell and NSControl classes do.
How Controls and Cells Interact gives more information on how controls and cells interact and how they operate.
Cell States describes the three states a control can have: on, off, or mixed. Although used primarily by NSButton, states are defined in NSCell so future subclasses can use them.
Represented Objects explains how to associate a cell with the object it represents.

Here are the tasks:

"Manipulating Cells and Controls" discusses various tips and techniques for dealing with cells and controls.
Changing the Cell for a Control describes how to change the NSCell subclass that a control uses.
Displaying Cell Values describes how some cells format and display their values as strings.
Validating Control Entries describes how to validate the contents of some cells, especially cells in a matrix or text field.
Using a Continuous Control describes how to set up a control so it sends its action message repeatedly while being pressed.
Subclassing NSCell and Subclassing NSControl describe how to create custom subclasses of NSCell and NSControl.
Using the System Control Tint describes how to use the system-wide control tint in your custom views and control cells.