Discovering Swift and the iOS Playground
This hour’s lesson marks the midpoint in our exploration of the Apple iOS development platform. It will give us a chance to sit back, catch our breath, and get a better idea of what it means to “code” for iOS. Both OS X and iOS share a common development environment and a common development language: Swift.
Swift provides the syntax and structure for creating applications on Apple platforms. Swift is a brand-new language developed internally in Apple that still has that “new language smell,” but also a few disconcerting knocks under the hood. It can seem a bit daunting at first, but after a few hours of practice, you’ll begin to feel right at home. This hour takes you through the steps you need to know to be comfortable with Swift and starts you down the path to mastering this unique and powerful language.
Object-Oriented Programming and Swift
To better understand the scope of this hour, take a few minutes to search for Swift or object-oriented programming in your favorite online bookstore. You will find quite a few books—lengthy books—on these topics. In this book, roughly 30 pages cover what other books teach in hundreds of pages. Although it’s not possible to fully cover Swift and object-oriented development in this single hour, we can make sure that you understand enough to develop fairly complex apps.
To provide you with the information you need to be successful in iOS development, this hour concentrates on fundamentals—the core concepts that are used repeatedly throughout the examples and tutorials in this book. The approach in this hour is to introduce you to a programming topic in general terms, and then look at how it will be performed when you sit down to write your application. Before we begin, let’s look a bit closer at Swift and object-oriented programming.
What Is Object-Oriented Programming?
Most people have an idea of what programming is and have even written a simple program. Everything from setting your DVR to record a show to configuring a cooking cycle for your microwave is a type of programming. You use data (such as times) and instructions (like “record”) to tell your devices to complete a specific task. This certainly is a long way from developing for iOS, but in a way the biggest difference is in the amount of data you can provide and manipulate and the number of different instructions available to you.
There are two primary development paradigms: imperative programming and object-oriented programming. First, imperative programming (a subset of which is called procedural programming) implements a sequence of commands that should be performed. The application follows the sequence and carries out activities as directed. Although there might be branches in the sequence or movement back and forth between some of the steps, the flow is from a starting condition to an ending condition, with all the logic to make things work sitting in the middle.
The problem with imperative programming is that it lends itself to growing, without structure, into an amorphous blob. Applications gain features when developers tack on bits of code here and there. Often, instructions that implement a piece of functionality are repeated over and over wherever something needs to take place. Procedural programming refers to an imperative programming structure that attempts to avoid repetition by creating functions (or procedures) that can be reused. This works to some extent, but long-term still often results in code bloat. The benefit of this approach, however, is that it is quite easy to pick up and learn: You create a series of instructions, and the computer follows them.
The Object-Oriented Approach
The other development approach, and what we use in this book, is object-oriented programming (OOP). OOP uses the same types of instructions as imperative development but structures them in a way that makes your applications easy to maintain and promotes code reuse whenever possible. In OOP, you create objects that hold the data that describes something along with the instructions to manipulate that data. Perhaps an example is in order.
Consider a program that enables you to track reminders. With each reminder, you want to store information about the event that will be taking place—a name, a time to sound an alarm, a location, and any additional miscellaneous notes that you may want to store. In addition, you need to be able to reschedule a reminder’s alarm time or completely cancel an alarm.
In the imperative approach, you have to write the steps necessary to track all the reminders, all the data in the reminders, check every reminder to see whether an alarm should sound, and so on. It’s certainly possible, but just trying to wrap your mind around everything that the application needs to do could cause some serious headaches. An object-oriented approach brings some sanity to the situation.
In an object-oriented model, you could implement a reminder as a single object. The reminder object would know how to store the properties such as the name, location, and so on. It would implement just enough functionality to sound its own alarm and reschedule or cancel its alarm. Writing the code, in fact, would be very similar to writing an imperative program that only has to manage a single reminder. By encapsulating this functionality into an object, however, we can then create multiple copies of the object within an application and have them each fully capable of handling separate reminders. No fuss and no messy code!
Most of the tutorials in this book make use of one or two objects, so don’t worry about being overwhelmed with OOP. You’ll see enough to get accustomed to the idea, but we’re not going to go overboard.
Another important facet of OOP is inheritance. Suppose that you want to create a special type of reminder for birthdays that includes a list of birthday presents that a person has requested. Instead of tacking this onto the reminder object, you could create an entirely new “birthday reminder” that inherits all the features and properties of a reminder and then adds in the list of presents and anything else specific to birthdays.