Building Cocoa Applications: A Step by Step Guide

Chapter 16. GraphPaper: A Multithreaded Application with a Display List

In this chapter, we’ll use the Evaluator back end that we built in Chapter 10 as the basis for an application that graphs single-valued functions. By the end of the chapter, the menu bar and main window of the application will look like those shown in Figure 16-1.

Figure 16-1. The GraphPaper application

In the process of developing this program, we’ll learn more about the drawRect: method, see how to construct a complicated image out of many individual pieces, and learn a little bit about threads.

GraphPaper’s Design

Conceptually, our program to graph a function will contain four main parts, as described in the list that follows.

Interface

Lets the user specify the function and graph parameters, and start and stop the graphing process

Pair generator

Takes the graph parameters set by the user and generates pairs of (x,y) points to be plotted

Graph builder

Takes the pairs from the pair generator and builds the graph’s data structure

Graph displayer

Takes the data structure and displays it on the screen

The Interface

We’ll build GraphPaper’s interface with Interface Builder (of course!). The interface will consist of a Cocoa NSForm object containing several text fields (“xmin”, “ymax”, etc., as shown in Figure 16-1), a button (labeled “Graph”) to start the graphing process, and a custom NSView called the GraphView. ...