Building Cocoa Applications: A Step by Step Guide

Adding Color to GraphPaper

In the remainder of this chapter, we’ll add color to our GraphPaper application. To do this, we’ll add a Preferences panel (users refer to it as a Preferences dialog) that will let the user choose three distinct colors for drawing the graph, the equation, and the axes.

To isolate the parts of the GraphView that deal solely with color, we’ll create a GraphView subclass called ColorGraphView. This way, we won’t need to make any changes to the GraphView class itself, yet we can use all of its functionality. This is called reusability of classes.

The user probably won’t want to change the graph’s colors every time the GraphPaper application is run, so we’ll put the Preferences panel in its own nib file rather than in MainMenu.nib. That way, the Preferences panel will be loaded and take up memory only when the user chooses to see it. The ColorGraphView class will have three NSColor instance variables, to keep track of the colors currently being used.

We’ll also set up a new class called PrefController to take care of modifying these instance variables when the Preferences panel is displayed. If the Preferences panel isn’t loaded, the ColorGraphView class will use reasonable defaults for the color instance variables. In Chapter 21, we’ll see how to set the values for these colors from the Mac OS X defaults database, application- defaults information stored in every user’s ~/Library/Preferences folder. (The application’s defaults database was introduced in ...