Learn to Program Your First iPad App
There is no better way to learn than by actually doing something, so let’s dive in by writing a really simple iPad app. The first application you will write is a Hello World app. Yes, the Hello World sample application is overdone, but don’t worry—you will be building more sophisticated applications later in this book. For now, it’s important to get your hands dirty with some code and the tools.
The goal for this chapter is to give you a sneak peek at the tools you will be using to build your iPad applications. If you are already familiar with Xcode, you may wish to skip ahead to Chapter 4, “Getting Started with Objective-C,” or Chapter 6, “Provisioning Your iPad.” If you are new to Xcode, please continue reading.
The rest of this chapter will guide you through the steps needed to create your first iPad application. The chapter does not go into detail about Xcode. Instead, those details are covered in the following chapters: Chapter 2, “Getting Started with Xcode,” and Chapter 3, “Getting Started with Interface Builder.”
Creating the Hello World Project
Let’s begin by launching Xcode. If you are running Mountain Lion (Mac OS X 10.8) and you downloaded Xcode from the Mac App Store, it is available in Launchpad, shown in Figure 1.1; otherwise, you can find it in your Applications folder. Click the Xcode icon to launch it.
Figure 1.1. The Xcode icon as seen in Launchpad
The first window you see after launching Xcode is the Welcome to Xcode screen, shown in Figure 1.2. You can do a number of things from this window, including creating a new project, connecting to a source code repository, going to the Xcode 4 User Guide (a tutorial on using Xcode), or visiting Apple’s Developer site.1 If you have created or opened Xcode projects in the past, you will also see a list of recent projects on the right side of this screen. You can open a recent project by selecting it from the list and clicking Open.
Figure 1.2. Welcome to Xcode window
Tucked away in the lower-left corner is the Open Other... button. You can click this button to open an existing Xcode project found on the file system. Next to this button is a check box indicating whether the Welcome to Xcode window is displayed when Xcode launches.
You want to create a new iPad application, so click the Create a new Xcode project button. This opens the new project window, as shown in Figure 1.3. Let’s explore this window for a moment before continuing. As you can see in the figure, the new project has three main sections:
- Target type
- Project template
- Template detail
Figure 1.3. The new project window in Xcode, with callouts on sections of Xcode’s user interface (1: target type; 2: project template; 3: template detail)
In section 1, you select the target type: iOS or Mac OS X. iPad applications run on iOS, so you can ignore the Mac OS X target type for now. Under iOS you can build two types of targets: Application and Framework & Library. The Application type is exactly what the name implies; you use it to build iPhone and iPad applications. The Library target type is for building reusable static libraries, which you can also ignore for now.
The Hello World application you are building is just that, an application. Thus, in section 1 under iOS, you select Application. When you do so, you’ll notice that the content in section 2 changes. Section 2 now displays the list of available templates for the selected target type. A template is used to generate the initial files needed for an Xcode project.
If you have spent time playing with your iPad, you may have noticed that there are some common application types, or styles. The templates listed in section 2 help speed the process of creating an application of a particular style. For example, if you wanted to create an application that looks similar to the Mail app on the iPad, you would select Master-Detail Application.
The Hello World application will consist of a single view, so select Single View Application from the list of templates. When you do so, notice that the content of the template detail section changes. This section shows a brief description of the template selected in the project template section.
Clicking the Next button takes you to the project options screen, shown in Figure 1.4. Project options vary slightly based on the template. Each template has options for the Product Name, Organization Name, Company Identifier, Bundler Identifier (which is completed for you based on the Company Identifier and Product Name), Class Prefix, and Device Family. Additional options that may be found on an application template include Use Storyboard, Use Automatic Reference Counting, Use Core Data, and Include Unit Tests. The application template you select determines which additional options are made available.
Figure 1.4. Project options for the Single View Application template
For the Hello World app you are building, enter “Hello World” for the Product Name. The Organization Name can be any value you like, as it is used only in the copyright message included in the comment section that is added to the top of each .h and .m file created by Xcode for the project.
For the Company Identifier, enter your name or company name using the reverse domain name format. (For example, com.kirbyturner is my individual name and com.whitepeaksoftware is my company name.) Chapter 6, “Provisioning Your iPad,” explains the relationship between the company and bundle identifiers and describes how they are used to form the App ID.
The Class Prefix can be used to append a string value to the beginning of each class generated by the application template. For the purpose of simplicity, you can leave the Class Prefix blank for this app.
Next, select iPad as the Device Family. There are three device family types in iOS: iPad, iPhone, and Universal. The device family iPad indicates that the app is designed for and runs on the iPad only. The iPhone device family indicates that the app is designed for the iPhone, and Universal says that the app is designed for and runs on both the iPad and the iPhone.
You do not need storyboard and unit tests in this Hello World app, so leave those options unselected. (Storyboarding is covered in Chapter 14, “Storyboarding in Xcode.”) But do select the Use Automatic Reference Counting option—it determines how memory of an object is managed, and is explained in the Memory Management section of Chapter 4, “Getting Started with Objective-C.” Click the Next button, choose a storage location for the Xcode project, and then click the Create button (shown in Figure 1.5).
Figure 1.5. Choose the location where your Xcode project is stored.
Congratulations! You just created your first iPad application. You don’t believe it? Click the Run button (shown in Figure 1.6), or press Command-R. Be sure the active schema is set to the iPad Simulator. If it is not, click it and change it to the simulator.
Figure 1.6. Xcode project window for the Hello World app
When you click Run, Xcode compiles the project, builds an application package, installs the application on the iPad Simulator, and finally launches the application inside the simulator. As you can see in Figure 1.7, the application is nothing more than a white screen. Guess what? You just built your first flashlight app for the iPad!
Figure 1.7. A “blank” single view app running in the iPad Simulator
You can take your newly created flashlight application and submit it to Apple for review. However, there is a high level of certainty that Apple will reject your masterpiece because of its lack of functionality. Besides, you are not done with this app. You want to build a Hello World application, and, as you can see, “Hello World” does not appear when this application is run. So let’s continue working on it.
First, stop the app, which is running in the simulator. You can do so by clicking the Stop button at the upper-left side of Xcode or by pressing Command-. in Xcode (not in the simulator). Now you’re ready to start modifying the app.