Beginning iOS 6 development

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For your convenience Apress has placed some of the front

matter material after the index. Please use the Bookmarks

and Contents at a Glance links to access them.

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v

Contents at a Glance

About the Authors�������������������������������������������������������������������������������������������������������������� xxi

About the Technical Reviewers ��������������������������������������������������������������������������������������� xxiii

■Chapter 1: Welcome to the Jungle�������������������������������������������������������������������������������������1

■Chapter 2: Appeasing the Tiki Gods���������������������������������������������������������������������������������11

■Chapter 3: Handling Basic Interaction�����������������������������������������������������������������������������43

■Chapter 4: More User Interface Fun ��������������������������������������������������������������������������������69

■Chapter 5: Autorotation and Autosizing ������������������������������������������������������������������������115

■Chapter 6: Multiview Applications ��������������������������������������������������������������������������������139

■Chapter 7: Tab Bars and Pickers �����������������������������������������������������������������������������������169

■Chapter 8: Introduction to Table Views �������������������������������������������������������������������������221

■Chapter 9: Navigation Controllers and Table Views�������������������������������������������������������269

■Chapter 10: Storyboards������������������������������������������������������������������������������������������������341

■Chapter 11: iPad Considerations �����������������������������������������������������������������������������������367

■Chapter 12: Application Settings and User Defaults������������������������������������������������������397

■Chapter 13: Basic Data Persistence ������������������������������������������������������������������������������435

■Chapter 14: Hey! You! Get onto iCloud! �������������������������������������������������������������������������481

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vi Contents at a Glance

■Chapter 15: Grand Central Dispatch, Background Processing, and You������������������������511

■Chapter 16: Drawing with Quartz and OpenGL ��������������������������������������������������������������545

■Chapter 17: Taps, Touches, and Gestures ����������������������������������������������������������������������585

■Chapter 18: Where Am I? Finding Your Way with Core Location and Map Kit���������������619

■Chapter 19: Whee! Gyro and Accelerometer! ����������������������������������������������������������������637

■Chapter 20: The Camera and Photo Library�������������������������������������������������������������������667

■Chapter 21: Collection View ������������������������������������������������������������������������������������������677

■Chapter 22: Application Localization�����������������������������������������������������������������������������691

■Appendix A: Where to Next? ������������������������������������������������������������������������������������������717

Index���������������������������������������������������������������������������������������������������������������������������������725

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1

Chapter 1

Welcome to the Jungle

So, you want to write iPhone, iPod touch, and iPad applications? Well, we can’t say that we blame

you. iOS, the core software of all of these devices, is an exciting platform that has been seeing

explosive growth since it first came out in 2007. The rise of the mobile software platform means that

people are using software everywhere they go. With the release of iOS 6, and the latest incarnation

of the iOS software development kit (SDK), things have only gotten better and more interesting.

What This Book Is

This book is a guide to help you get started down the path to creating your own iOS applications.

Our goal is to get you past the initial difficulties, to help you understand the way iOS applications

work and how they are built.

As you work your way through this book, you will create a number of small applications, each

designed to highlight specific iOS features and to show you how to control or interact with those

features. If you combine the foundation you’ll gain through this book with your own creativity and

determination, and then add in the extensive and well-written documentation provided by Apple,

you’ll have everything you need to build your own professional iPhone and iPad applications.

Tip Dave, Jack, Jeff, and Fredrik have set up a forum for this book. It’s a great place to meet like-minded

folks, get your questions answered, and even answer other people’s questions. The forum is at

http://forum.learncocoa.org. Be sure to check it out!

What You Need

Before you can begin writing software for iOS, you’ll need a few items. For starters, you’ll need

an Intel-based Macintosh, running Lion (OS X 10.7) or later. Any recent Intel-based Macintosh

computer—laptop or desktop—should work just fine.

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2 CHAPTER 1: Welcome to the Jungle

You’ll also need to sign up to become a registered iOS developer. Apple requires this step before

you’re allowed to download the iOS SDK.

To sign up as a developer, just navigate to http://developer.apple.com/ios/. That will bring you to

a page similar to the one shown in Figure 1-1.

Figure 1-1. Apple’s iOS Dev Center website

First, click on Log in. You’ll be prompted for your Apple ID. If you don’t have an Apple ID, click

Join now, create one, and then log in. Once you are logged in, you’ll be taken to the main iOS

development page. Not only will you see a link to the SDK download, but you’ll also find links to a

wealth of documentation, videos, sample code, and the like—all dedicated to teaching you the finer

points of iOS application development.

The most important tool you’ll be using to develop iOS applications is called Xcode. Xcode is

Apple’s integrated development environment (IDE). Xcode includes tools for creating and debugging

source code, compiling applications, and performance tuning the applications you’ve written.

You can download Xcode from the Mac App Store, which you can access from your Mac’s Apple

menu.

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CHAPTER 1: Welcome to the Jungle 3

As the versions of the SDK and Xcode evolve, the mechanism for downloading them will also change. Starting with the

release of Xcode 4.3, Apple has been publishing the current “stable” version of Xcode and the iOS SDK on the Mac App

Store, while simultaneously often providing developers the ability to download preview versions of upcoming releases

from their developer site. Bottom line: you want to download the latest released (non-beta) version of Xcode and the iOS

SDK, so use the Mac App Store.

This book has been written to work with the latest version of the SDK. In some places, we have chosen to use new

functions or methods introduced with iOS 6 that may prove incompatible with earlier versions of the SDK. We’ll be sure to

point those situations out as they arise in this book.

Be sure to download the latest and greatest source code archives from http://iphonedevbook.com or from the

book’s forum at http://forum.learncocoa.org. We’ll update the code as new versions of the SDK are released, so

be sure to check the site periodically.

Developer Options

The free SDK download option includes a simulator that will allow you to build and run iPhone and

iPad apps on your Mac. This is perfect for learning how to program for iOS. However, the simulator

does not support many hardware-dependent features, such as the accelerometer and camera. Also,

the free option will not allow you to download your applications onto your actual iPhone or other

device, and it does not give you the ability to distribute your applications on Apple’s App Store. For

those capabilities, you’ll need to sign up for one of the other options, which aren’t free:

 The Standard program costs $99/year. It provides a host of development tools

and resources, technical support, distribution of your application via Apple’s App

Store, and, most important, the ability to test and debug your code on an iOS

device, rather than just in the simulator.

 The Enterprise program costs $299/year. It is designed for companies

developing proprietary, in-house iOS applications.

For more details on these programs, visit http://developer.apple.com/programs/ios and

http://developer.apple.com/programs/ios/enterprise to compare the two.

Because iOS supports an always-connected mobile device that uses other companies’ wireless

infrastructure, Apple has needed to place far more restrictions on iOS developers than it ever has on Mac

developers (who are able—at the moment anyway—to write and distribute programs with absolutely no

oversight or approval from Apple). Even though the iPod touch and the Wi-Fi-only versions of the iPad

don’t use anyone else’s infrastructure, they’re still subject to these same restrictions.

Apple has not added restrictions to be mean, but rather as an attempt to minimize the chances of

malicious or poorly written programs being distributed that could degrade performance on the shared

network. Developing for iOS may appear to present a lot of hoops to jump through, but Apple has

expended quite an effort to make the process as painless as possible. And also consider that $99 is

still much less than buying, for example, Visual Studio, which is Microsoft’s software development IDE.

SDK VERSIONS AND SOURCE CODE FOR THE EXAMPLES

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4 CHAPTER 1: Welcome to the Jungle

This may seem obvious, but you’ll also need an iPhone, iPod touch, or iPad. While much of your

code can be tested using the iOS simulator, not all programs can be. And even those that can run

on the simulator really need to be thoroughly tested on an actual device before you ever consider

releasing your application to the public.

Note If you are going to sign up for the Standard or Enterprise program, you should do it right now.

The approval process can take a while, and you’ll need that approval to be able to run your applications

on an actual device. Don’t worry, though, because all the projects in the first several chapters and the

majority of the applications in this book will run just fine on the iOS simulator.

What You Need to Know

This book assumes that you already have some programming knowledge. It assumes that you

understand the fundamentals of object-oriented programming (you know what objects, loops, and

variables are, for example). It also assumes that you are familiar with the Objective-C programming

language. Cocoa Touch, the part of the SDK that you will be working with through most of this book,

uses the latest version of Objective-C, which contains several new features not present in earlier

versions. But don’t worry if you’re not familiar with the more recent additions to the Objective-C

language. We highlight any of the new language features we take advantage of, and explain how

they work and why we are using them.

You should also be familiar with iOS itself, as a user. Just as you would with any platform for which

you wanted to write an application, get to know the nuances and quirks of the iPhone, iPad, or iPod

touch. Take the time to get familiar with the iOS interface and with the way Apple’s iPhone and/or

iPad applications look and feel.

NEW TO OBJECTIVE-C?

If you have not programmed in Objective-C before, here are a few resources to help you get started:

• Check out Learn Objective-C on the Mac: For OS X and iOS (2nd edition, Apress, 2012):,

an excellent and approachable introduction to Objective-C by Mac-programming experts Scott Knaster,

Waqar Malik, and Mark Dalrymple: http://www.apress.com/book/view/9781430241881.

• See Apple’s introduction to the language, Learning Objective-C: A Primer.

• Take a look at The Objective-C Programming Language, a very detailed and extensive description of the

language and a great reference guide.

The last two are available from http://developer.apple.com/library/ios/navigation/. That last one is also

available as a free download from iBooks on your iPhone, iPod touch, or iPad. It’s perfect for reading on the go! Apple

has released several developer titles in this format, and we hope that more are on the way. Search for “Apple developer

publications” in iBooks to find them.

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CHAPTER 1: Welcome to the Jungle 5

What’s Different About Coding for iOS?

If you have never programmed in Cocoa or its predecessors NeXTSTEP or OpenStep, you may

find Cocoa Touch—the application framework you’ll be using to write iOS applications—a little alien.

It has some fundamental differences from other common application frameworks, such as those

used when building .NET or Java applications. Don’t worry too much if you feel a little lost at first.

Just keep plugging away at the exercises, and it will all start to fall into place after a while.

If you have written programs using Cocoa or NeXTSTEP, a lot in the iOS SDK will be familiar to

you. A great many classes are unchanged from the versions that are used to develop for OS X.

Even those that are different tend to follow the same basic principles and similar design patterns.

However, several differences exist between Cocoa and Cocoa Touch.

Regardless of your background, you need to keep in mind some key differences between iOS

development and desktop application development. These differences are discussed in the

following sections.

Only One Active Application

On iOS, only one application can be active and displayed on the screen at any given time. Since

iOS 4, applications have been able to run in the background after the user presses the “home”

button, but even that is limited to a narrow set of situations, and you must code for it specifically.

When your application isn’t active or running in the background, it doesn’t receive any attention

whatsoever from the CPU, which will wreak havoc with open network connections and the like. iOS

allows background processing, but making your apps play nicely in this situation will require some

effort on your part.

Only One Window

Desktop and laptop operating systems allow many running programs to coexist, each with the ability

to create and control multiple windows. However, iOS gives your application just one “window” to

work with. All of your application’s interaction with the user takes place inside this one window, and

its size is fixed at the size of the screen.

Limited Access

Programs on a computer pretty much have access to everything the user who launched them does.

However, iOS seriously restricts what your application can access.

You can read and write files only from the part of iOS’s file system that was created for your

application. This area is called your application’s sandbox. Your sandbox is where your application

will store documents, preferences, and every other kind of data it may need to retain.

Your application is also constrained in some other ways. You will not be able to access low-number

network ports on iOS, for example, or do anything else that would typically require root or

administrative access on a desktop computer.

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6 CHAPTER 1: Welcome to the Jungle

Limited Response Time

Because of the way it is used, iOS needs to be snappy, and it expects the same of your application.

When your program is launched, you need to get your application open, preferences and data

loaded, and the main view shown on the screen as fast as possible—in no more than a few seconds.

At any time when your program is running, it may have the rug pulled out from under it. If the user

presses the home button, iOS goes home, and you must quickly save everything and quit. If you

take longer than five seconds to save and give up control, your application process will be killed,

regardless of whether you are finished saving.

Note that since iOS 5, this situation has been ameliorated somewhat by the existence of new API

that allows your app to ask for additional time to work when it’s about to go dark.

Limited Screen Size

The iPhone’s screen is really nice. When introduced, it was the highest resolution screen available on

a consumer device, by far.

But the iPhone display just isn’t all that big, and as a result, you have a lot less room to work with

than on modern computers. The screen is just 320×480 on the first few iPhone generations, and

was later doubled in both directions to 640×960 with the introduction of the iPhone 4’s retina

display. This was recently increased further to 640×1136 on the iPhone 5. That sounds like a decent

number of pixels, but keep in minde that these retina displays are crammed into pretty small form

factors, so you can’t count on fitting more controls or anything like that. This has a big impact on the

kinds of applications and interactivity you can offer on an iPhone.

The iPad increases the available space a bit by offering a 1024×768 display, but even today, that’s

not so terribly large. To give an interesting contrast, at the time of writing, Apple’s least expensive

iMac supports 1920×1080 pixels, and its least expensive notebook computer, the 11-inch MacBook

Air, supports 1366×768 pixels. On the other end of the spectrum, Apple’s largest current monitor,

the 27-inch LED Cinema Display, offers a whopping 2560×1440 pixels. Note that the 3rd generation

iPad released in the spring of 2012 (which Apple confusingly calls the “new iPad” instead of

incrementing the number from the previous iPad 2) actually doubles the screen resolution in both

directions. But as with the retina iPhones, that 2048×1536 screen is in the same physical space as

the old screen was, so you can’t really count on using those pixels the same way you would on a

traditional screen.

Limited System Resources

Any old-time programmers who are reading this are likely laughing at the idea of a machine with

at least 512MB of RAM and 16GB of storage being in any way resource-constrained, but it is

true. Developing for iOS is not, perhaps, in exactly the same league as trying to write a complex

spreadsheet application on a machine with 48KB of memory. But given the graphical nature of iOS

and all it is capable of doing, running out of memory is very easy.

The iOS devices available right now have either 512MB (iPhone 4, iPhone 4S, iPad 2), or 1024MB of

physical RAM (iPhone 5, new iPad), though that will likely increase over time. Some of that memory

is used for the screen buffer and by other system processes. Usually, no more than half of that

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CHAPTER 1: Welcome to the Jungle 7

memory is left for your application to use, and the amount can be considerably less, especially now

that apps can run in the background.

Although that may sound like it leaves a pretty decent amount of memory for such a small computer,

there is another factor to consider when it comes to memory on iOS. Modern computer operating

systems like OS X will take chunks of memory that aren’t being used and write them out to disk

in something called a swap file. The swap file allows applications to keep running, even when

they have requested more memory than is actually available on the computer. iOS, however, will not

write volatile memory, such as application data, out to a swap file. As a result, the amount of memory

available to your application is constrained by the amount of unused physical memory in the iOS device.

Cocoa Touch has built-in mechanisms for letting your application know that memory is getting low.

When that happens, your application must free up unneeded memory or risk being forced to quit.

No Garbage Collection, but…

We mentioned earlier that Cocoa Touch uses Objective-C, but one of the key new features of that

language is not available with iOS: Cocoa Touch does not support garbage collection. The need to

do manual memory management when programming for iOS has been a bit of a stumbling block

for many programmers new to the platform, especially those coming from languages that offer

garbage collection.

With the version of Objective-C supported by the latest versions of iOS, however, this particular

stumbling block is basically gone. This is thanks to a feature called Automatic Reference Counting

(ARC), which gets rid of the need to manually manage memory for Objective-C objects. ARC not

only serves as a worthy replacement to garbage collection, it’s actually better in most respects,

so that starting in OS X 10.8 it’s now become the default memory management technology, and

garbage collection has been deprecated there in favor of ARC. We’ll talk about ARC in Chapter 3.

Some New Stuff

Since we’ve mentioned that Cocoa Touch is missing some features that Cocoa has, it seems only

fair to mention that the iOS SDK contains some functionality that is not currently present in Cocoa or,

at least, is not available on every Mac:

 The iOS SDK provides a way for your application to determine the iOS device’s

current geographic coordinates using Core Location.

 Most iOS devices have built-in cameras and photo libraries, and the SDK

provides mechanisms that allow your application to access both.

 iOS devices have a built-in accelerometer (and, in the latest iPhone and iPod

touch, a gyroscope) that lets you detect how your device is being held and

moved.

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8 CHAPTER 1: Welcome to the Jungle

A Different Approach

Two things iOS devices don’t have are a physical keyboard and a mouse, which means you have

a fundamentally different way of interacting with the user than you do when programming for a

general-purpose computer. Fortunately, most of that interaction is handled for you. For example, if

you add a text field to your application, iOS knows to bring up a keyboard when the user touches

that field, without you needing to write any extra code.

Note Current devices do allow you to connect an external keyboard via Bluetooth, which gives you

a nice keyboard experience and saves some screen real estate, but this is still a fairly rare usage.

Connecting a mouse is still not an option.

What’s in This Book

Here is a brief overview of the remaining chapters in this book:

 In Chapter 2, you’ll learn how to use Xcode’s partner in crime, Interface Builder,

to create a simple interface, placing some text on the screen.

 In Chapter 3, you’ll start interacting with the user, building a simple application

that dynamically updates displayed text at runtime based on buttons the user

presses.

 Chapter 4 will build on Chapter 3 by introducing you to several more of iOS’s

standard user-interface controls. We’ll also demonstrate how to use alerts

and action sheets to prompt users to make a decision or to inform them that

something out of the ordinary has occurred.

 In Chapter 5, we’ll look at handling autorotation and autosize attributes,

the mechanisms that allow iOS applications to be used in both portrait and

landscape modes.

 In Chapter 6, we’ll move into more advanced user interfaces and explore

creating applications that support multiple views. We’ll show you how to change

which view is being shown to the user at runtime, which will greatly enhance the

potential of your apps.

 Tab bars and pickers are part of the standard iOS user interface. In Chapter 7,

we’ll look at how to implement these interface elements.

 In Chapter 8, we’ll cover table views, the primary way of providing lists of data to

the user and the foundation of hierarchical navigation-based applications. You’ll

also see how to let the user search in your application data.

 One of the most common iOS application interfaces is the hierarchical list that

lets you drill down to see more data or more details. In Chapter 9, you’ll learn

what’s involved in implementing this standard type of interface.

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CHAPTER 1: Welcome to the Jungle 9

 iOS developers have traditionally built user interfaces for their apps using nib

files. This is still a fully supported development style, but nowadays you can do

even more with your designs using storyboards. Chapter 10 covers this great

new feature.

 The iPad, with its different form factor from the other iOS devices, requires a

different approach to displaying a GUI and provides some components to help

make that happen. In Chapter 11, we’ll show you how to use the iPad-specific

parts of the SDK.

 In Chapter 12, we’ll look at implementing application settings, which is iOS’s

mechanism for letting users set their application-level preferences.

 Chapter 13 covers data management on iOS. We’ll talk about creating objects

to hold application data and see how that data can be persisted to iOS’s file

system. We’ll also discuss the basics of using Core Data, which allows you to

save and retrieve data easily.

 In iOS 5 Apple introduced iCloud, which allows your document to store data

online and sync it between different instances of the application. Chapter 14

shows you how to get started with iCloud.

 Since iOS 4, developers have access to a new approach to multithreaded

development using Grand Central Dispatch, and also have the ability to make

their apps run in the background in certain circumstances. In Chapter 15, we’ll

show you how that’s done.

 Everyone loves to draw, so we’ll look at doing some custom drawing in Chapter 16.

We’ll use basic drawing functions in Quartz 2D and OpenGL ES.

 The multitouch screen common to all iOS devices can accept a wide variety of

gestural inputs from the user. In Chapter 17, you’ll learn all about detecting basic

gestures, such as the pinch and swipe. We’ll also look at the process of defining

new gestures and talk about when new gestures are appropriate.

 iOS is capable of determining its latitude and longitude thanks to Core Location.

In Chapter 18, we’ll build some code that makes use of Core Location to figure

out where in the world your device is and use that information in our quest for

world dominance.

 In Chapter 19, we’ll look at interfacing with iOS’s accelerometer and gyroscope,

which is how your device knows which way it’s being held, the speed and

direction in which it is moving, and where in the world it’s located. We’ll explore

some of the fun things your application can do with that information.

 Nearly every iOS device has a camera and a library of pictures, both of which

are available to your application, if you ask nicely! In Chapter 20, we’ll show you

how to ask nicely.

 From the beginning, all sorts of iOS applications have made use of table views

to display dynamic, vertically scrolling lists of components. In iOS 6, Apple

has introduced a new class called UICollectionView which takes this concept

a few steps further, giving developers lots of new flexibility in laying out visual

components. Chapter 21 will get you up and running with collection views.

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10 CHAPTER 1: Welcome to the Jungle

 iOS devices are currently available in more than 90 countries. In Chapter 22,

we’ll show you how to write your applications in such a way that all parts can be

easily translated into other languages. This helps expand the potential audience

for your applications.

 By the end of this book, you’ll have mastered the fundamental building blocks

for creating iPhone and iPad applications. But where do you go from here? In

the appendix, we’ll explore the logical next steps for you to take on your journey

to master the iOS SDK.

What’s New in This Update?

Since the first edition of this book hit the bookstores, the growth of the iOS development community

has been phenomenal. The SDK has continually evolved, with Apple releasing a steady stream of

SDK updates.

Well, we’ve been busy, too! The second we found out about iOS SDK 6, we immediately went to

work, updating every single project to ensure not only that the code compiles using the latest version

of Xcode and the SDK, but also that each one takes advantage of the latest and greatest features

offered by Cocoa Touch. We made a ton of subtle changes throughout the book, and added a good

amount of substantive changes as well, including a brand-new chapter on the new collection view

that Apple added to iOS 6. And, of course, we reshot every screen shown in the book.

Are You Ready?

iOS is an incredible computing platform and an exciting new frontier for your development pleasure.

Programming for iOS is going to be a new experience—different from working on any other platform.

For everything that looks familiar, there will be something alien, but as you work through the book’s

code, the concepts should all come together and start to make sense.

Keep in mind that the exercises in this book are not simply a checklist that, when completed,

magically grants you iOS developer guru status. Make sure you understand what you did and why

before moving on to the next project. Don’t be afraid to make changes to the code. Observing

the results of your experimentation is one of the best ways you can wrap your head around the

complexities of coding in an environment like Cocoa Touch.

That said, if you have your iOS SDK installed, turn the page. If not, get to it! Got it? Good. Then let’s go!

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Chapter 2

Appeasing the Tiki Gods

As you’re probably well aware, it has become something of a tradition to call the first project in any

book on programming “Hello, World.” We considered breaking with this tradition, but were scared

that the tiki gods would inflict some painful retribution on us for such a gross breach of etiquette.

So, let’s do it by the book, shall we?

In this chapter, we’re going to use Xcode to create a small iOS application that will display the text

“Hello, World!” We’ll look at what’s involved in creating an iOS application project in Xcode, work

through the specifics of using Xcode’s Interface Builder to design our application’s user interface,

and then run our application on the iOS simulator. After that, we’ll give our application an icon to

make it feel more like a real iOS application.

We have a lot to do here, so let’s get going.

Setting Up Your Project in Xcode

By now, you should have Xcode and the iOS SDK installed on your machine. You should also download

the book project archive from the iPhone Dev Book web site (http://www.iphonedevbook.com/).

While you’re at it, take a look at the book forums at http://forum.learncocoa.org/. The book forums

are a great place to discuss iOS development, get your questions answered, and meet up with

like-minded people.

Note Even though you have the complete set of project files at your disposal in this book’s project

archive, you’ll get more out of the book if you create each project by hand, rather than simply running

the version you downloaded. By doing that, you’ll gain familiarity and expertise working with the various

application development tools.

There’s no substitute for actually creating applications; software development is not a spectator sport.

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