Building Cocoa Applications: A Step by Step Guide

Adding Defaults to GraphPaper

In this section, we’ll modify the GraphPaper application to work with the defaults database. We will do this by making changes to both the Controller and the ColorGraphView classes.

Cocoa applications use a single instance of the Foundation class NSUserDefaults for managing the defaults database. Apple’s documentation notes that the NSUserDefaults class is not thread-safe, so you should use it only from your application’s main thread.

To use the NSUserDefaults class, you must first decide what default values your application will need to store. Each of these values should be given a name that will be its key in the defaults database. For each value, you must also decide upon a representation — that is, how the representation will be stored. Table 21-3 shows the defaults that we will use for GraphPaper.

Table 21-3. Defaults for the GraphPaper application

Default name	#define	Our default
AxesColor	GP_AxesColor	[NSColor red]
LabelColor	GP_LabelColor	[NSColor blue]
GraphColor	GP_GraphColor	[NSColor black]
xstep	GP_xstep	0.1
xmin	GP_xmin	-10.0
xmax	GP_xmax	10.0
ymin	GP_ymin	-5.0
ymax	GP_ymax	5.0
formula	GP_Formula	cos(x)
GraphPaper window frame	Not needed	NSMakeRect(0,0,500,500)

Once you have decided on the default values that your application will be using, you need to write the code that will install these into the default registration table. This table will provide the default ...