Now that you know how to build applications, let’s look at the ingredients of an application in more detail. As mentioned in Chapter 3, applications are built from a kit of parts called objects. iOS includes a vast selection you can use in your app. You can—and often do—customize objects to add extra features.
Technically, iOS is an object-oriented system. This doesn’t just mean that iOS uses standardized and customizable kit parts. It also defines how iOS exchanges information with your app and how iOS and your app communicate with each other.
Let’s look at what this means in practice. Follow these steps:
1. Launch Xcode, if it isn’t running already.
2. Create a new project using the SingleView Application Template. The name doesn’t matter. If you saved the project when you created it in Chapter 3, you can reload it instead of creating it again.
3. If it isn’t already open, click the reveal triangle to the left of the top group in the Project navigator, as shown in Figure 4.1. You’ll see four files: one pair labeled with the word “AppDelegate” and the other with ViewController. These two files hold the core of the app.
4. Click the ViewController.m file to load it into the editor.
You’ll see the code in Figure 4.1. In the rest of this chapter, we’ll outline what the code does—without looking at it in too much detail.
Apps are message based. You must understand how messaging works before you can understand app design.
iOS uses ...