In this chapter, we took a close look at events and the responder chain and saw how they interact with the NSWindow object. We’ll periodically revisit these topics throughout the rest of the book, looking more closely at how events interact with the NSView class.

This chapter also marks the end of the evolution of our Calculator application. We’ve certainly covered a lot of ground while developing it, and it sure was fun!

In the next chapter, we’ll learn more about the system software that underlies Mac OS X and Cocoa. Then, in Chapter 10, we’ll start on a new application — MathPaper — which we’ll use to learn about interprocess communication and controlling multiple main windows.