Sample chapter 1 - Amazon Web Services
Contents
1. This is maintained by an NSAutoreleasePool release Reduces the object s memory count by 1 retain Increases the object s memory count by 1 For more information on memory management including a look at the copy method and how this all interacts with properties look at Manning s Objective C Fundamentals Christopher Fairbairn Collin Ruffenach and Johannes Fahrenkrug 2011 A good description of memory management rules is also found in the Memory Management Programming Guide on the Mac Developer Library website Event response The next to last category of methods that we examine for iOS is event response Unlike object creation and memory management we tackle this issue only briefly because it s much better documented in chapter 6 The topic is important enough that we want to offer a quick overview of it now Events can appear on the iPhone or iPad in three main ways through bare events or actions through delegated events and through notification Whereas the meth ods of our earlier topics all derived from NSObject event response instead comes from the UIResponder object whereas notification comes from the NSNotification Center You won t have to worry about accessing responder methods and properties iOS s methods 15 because UIResponder is the parent of most UIKit objects but the NSNotification Center requires special access EVENTS AND ACTIONS Most user input results in an event being placed2. I VAMNIO An d Ch i nnc f nr i D h nno i Af t Adi ples and olu LIONS TOF IF NONe GIF dC J Harrington B Trebitowski C Allen S Appelcline SAMPLE CHAPTER LL MANNING 10S 4 in Action by Jocelyn Harrington Brandon Trebitowski Christopher Allen Shannon Appelcline Chapter 1 Copyright 2011 Manning Publications brief contents OMON OO RWNH ER NNNRFPRPRRB RRB RBBB NURPOOANAOBKRWBNHRO Introducing iOS 4 with iPhone and iPad 1 Learning Objective C 20 Using Xcode4 31 Xcode and debugging 58 Basic view controllers 75 Monitoring events and actions 93 Advanced view controllers 117 Data actions preferences and files 146 Data advanced techniques 166 Positioning accelerometers location and the compass 195 Media images and the camera 219 Media audio and recording 239 Graphics Quartz Core Animation and OpenGL 258 The web web views and internet protocols 287 Peer to peer connections using Game Kit 311 Using Event Kit on the iPhone and iPad 332 Local and Push notification services 347 The Map Kit framework 363 In app purchasing using Store Kit 378 Making money with iAd 393 Introducing multitasking 407 Multitasking in depth 425 v Introducing iOS 4 with iPhone and iPad This chapter covers Understanding Apple s iPhone and iPad technology Installing the iOS 4 SDK Anatomy of iOS Turning your idea into an iOS application The iPhone and iPad provide an unforgettable user expe
3. ll return to soon Windows and views As the UI classes demonstrate iOS is deeply rooted in the idea of a graphical user interface Therefore let s finish our introduction to iOS by looking at some of the main graphical abstractions embedded in the UIKit There are three major abstrac tions windows views and view controllers A window is something that spans the device s entire screen An application usually has only one and it s the overall container for everything your application does A view is the content holder in your application You may have several of them each covering different parts of the window or doing different things at different times They re all derived from the UIView class But don t think of a view as a blank container Almost any object you use from UIKit will be a subclass of UIView that fea tures a lot of behavior of its own Among the major subclasses of UIView are UIControl which gives you buttons sliders and other items with which users may manipulate your program and UIScrollableView which gives users access to more text than can appear at once A view controller does what its name suggests It acts as the controller element of the Model View Controller triad and in the process manages a view sometimes called an application view As such it takes care of events and updating for your view In this book we ve divided view controllers into two types Basic view controllers man age a screen
4. a data source which is an object again usually a view controller that promises to do the data setup and control for another object again usually a view Delegation and data sourcing are each controlled by a protocol which is a set of methods the delegate or data source agrees to respond to For example a table s dele gate might have to respond to a method that alerts it when a row in the table has been selected Similarly a table s data source might describe what all the rows of the table look like Delegates and data sources fit cleanly into the MVC model used by Objective C because they allow a view to hand off its work to its controller without having to worry about where each of those objects is in the responder chain NOTIFICATIONS Standard event response and delegation represent two ways that objects can be alerted to standard events such as fingers touching the screen A third method can also be used to program many different sorts of activities such as the device s orienta tion changing or a network connection closing the notification Objects register to receive a certain type of notification with the NSNotification Center and afterward may process those notifications accordingly Again we ll discuss this topic in chapter 6 16 15 4 CHAPTER 1 Introducing iOS 4 with iPhone and iPad Lifecycle management In this discussion we ve neglected a topic how to recognize when objects are being created and des
5. into a responder chain This is a linked set of objects that for the most part goes backward up through the view hierarchy Any input is captured by the first responder which tends to be the object the user is directly interacting with If that object can t resolve the input it sends it up to its super view for example a label might send it up to its full screen view then to its super view all the way up the chain up through the views then up through the view controllers If input gets all the way up the view hierarchy to the window object it s next sent to the application itself which tends to pass it off to an application delegate as a last resort Any of these objects can choose to handle an event which stops its movement up the responder chain Following the standard MVC model you ll often build event response into UIViewController objects which are pretty far up the responder chain For any UIControl objects such as buttons sliders and toggles events are often turned into actions Whereas events report touches to the screen actions instead report manipulations of the controls and are easier to read Actions follow a slightly different hierarchy of response DELEGATES AND DATA SOURCES Events can be sent to an object in a way other than via a first responder through a del egate This is an object usually a view controller that says it will take care of events for another object usually a view It s close kin to
6. re work ing on native apps because you don t have to get your code signed by Apple to test it out Instruments is a program that allows you to dynamically debug profile and trace your program If you were creating web apps we would have to point you to a slew of browsers add ons and remote websites to do this sort of work but for your native apps that s all incorporated into this one package Getting ready for the SDK 7 Dashcode is listed here only for the sake of completeness because it s part of the Developer area It s a graphical development environment that s used to cre ate web based programs incorporating HTML CSS and JavaScript Dashcode is used when developing for the web you won t use it with the 10S SDK JUMPING AHEAD If you d prefer to immediately dive into your first program HelloWorld head to chap ter 3 You can then pop back here to see what it all means Figure 1 3 shows the most important developer tools In addition to the visible tools that you ve downloaded into Developer you ve also downloaded the entire set of iOS frameworks a huge collection of header files and source code all written in Objective C that will greatly simplify your programming experience In the next chapter we ll look at Objective C the SDK s programming language Rather than jumping straight into your first program we instead want to touch on these founda tional topics In the next section we ll exami
7. to get programming y ersion 4 of the iOS SDK adds powerful new features like even if you re new to Objective C iOS 4 in Action written for Xcode 4 is a detailed hands on guide that goes from setting up your development environment through your first coding steps all the way to creating a polished commercial iOS 4 application You ll run through examples from a variety of areas including a chat client a video game an interac tive map and background audio You ll also learn how the new iOS 4 features apply to your existing iOS 3 based apps This book will help you become a confident well rounded iOS 4 developer What s Inside e Full coverage of iOS SDK 4 3 e Mastering Xcode 4 e Multitasking for iPhone and iPad e Game Center iAd and AirPrint e Local and push notification e Implementing in app purchasing No previous iPhone or iPad know how needed Familiarity with C Cocoa or Objective C helps but is not required Jocelyn Harrington is an experienced full time mobile developer with a dozen entries in the App Store Brandon Trebitowski Christopher Allen and Shannon Appelcline are the authors of the previous edition iPhone and iPad in Action For access to the book s forum and a free ebook for owners of this book go to manning com iOS4inAction 44 99 Can 51 99 INCLUDING eBOOK The best iOS development book and the first to feature Xcode 4 Alex Curylo Trollwerks Inc All the informa
8. Ad from chapter 20 you ll be able to make money with your application in no time You don t have to build an application for profit Simply creating a cool application and learning a new programming technique is fun and rewarding in itself The 1 7 Summary 19 bottom line is if you re planning to distribute your application through the App Store make sure you read and follow the application guidelines from the iOS Developer Center Finally stay focused and don t give up Learning a new programming language isn t easy Try listing the key features for your application and focus on the most important ones throughout the development process Unless you have unlimited resources it will be hard to put all the features you want inside one application And even if you manage to it may be too hard for users to figure out how to use your app Remember sometimes less is more Summary In this chapter we first explored iOS on the iPhone and iPad and then we explained how to install the iOS SDK on your Mac We also covered the anatomy of iOS includ ing objects classes and methods providing the backdrop for coding in Objective C which follows in the next chapter With the program environment ready you can start the journey with iOS development iPHONE iPAD DEVELOPMENT 10S amp in action Harrington Trebitowski e Allen e Appelcline multitasking GCD blocks and iAds With the release of Xcode 4 it s easier than ever
9. OS SDK in the folder that pops up to start the installation process as shown in figure 1 2 This will bring you through the entire Warning installation dangers install process which will probably take The default installation of Xcode and 20 40 minutes You ll also get a few licens iOS SDK will replace any existing ing agreements that you need to sign off Apple development tools you have You ll still be able to do regular Apple development but you ll be working with a slightly more bleeding edge development environment on including the iPhone Licensing Agreement which lists some restrictions on what you ll be able to build for the iOS based devices 10S SDK LICENSING RESTRICTIONS Although Apple is making the iOS SDK widely available for public programming the company has placed some restrictions on what you can do with it We expect these restrictions to change as the SDK program evolves but what follows are some of the limitations at the time of this writing Among the most notable technical restrictions you can t use the code to create plug ins nor can you use it to download non SDK code It was the latter that appar ently spoiled Sun s original plans to port Java over to the iPhone You also can use only Apple s published APIs In addition there are numerous privacy related restrictions the most important of which is that you can t log the user s location without permis sion Finally Apple has some specific
10. OTE Xcode 4 is a free download for all members of the iOS Developer Pro gram which costs US 99 per year If you re not an 10S Developer Program member you can purchase Xcode 4 from the Mac App Store for US 4 99 or download Xcode 3 for free THE APPLE DOCS AND THE SDK To see the full API documentation as well as sample code visit http developer apple com devcenter ios It contains a few introductory papers of which we think the best are 10S Overview and Learning Objective C A Primer plus the complete class and protocol references for the SDK Getting ready for the SDK 5 As we ll discuss in the next chapter you can also access all of these docs from inside Xcode We usually find Xcode a better interface because it allows you to click through from your source code to your local documents Nonetheless the website is a great source of information when you don t have Xcode handy Because they tend to be updated relatively frequently we ve been constantly aware of Apple s documents while writing this book and we ve done our best to ensure that what we include complements Apple s information We ll continue to provide you with introductions to topics and to point you toward the references when there s a need for in depth information After you ve downloaded the SDK you ll find that it leaves a disk image sitting on your hard drive Double click it to mount the disk image and then double click Xcode and i
11. application restrictions including restrictions on apps that incorporate pornography or other objectionable content Xcode and iOS SDK Figure 1 2 Double clicking Xcode and iOS SDK starts your installation About Xcode and iOS SDK Xcode and iOS SDK 13 2 CHAPTER 1 Introducing iOS 4 with iPhone and iPad In order for your program to run on iPhones and iPads you ll need an Apple cer tificate and Apple maintains the right to refuse your cert if it doesn t like what you re doing If you re planning to write anything that might be questionable you should probably check whether Apple is likely to approve it first For example the most used third party software package that isn t available natively is Flash This book is going to cover how to develop an app on iPhone or iPad with the iOS SDK But there s another way to deliver an application to iPhone or iPad using HTML5 JavaScript for web apps We won t cover web application development in this book When the SDK finishes installing you ll find it in the Developer directory of your Mac system disk Most of the programs appear in Developer Applications which we suggest you make accessible using the Add to Sidebar feature in the Finder The iOS Simulator is located separately at Developer Platforms iPhoneSimulator platform Developer Applications Because this is off on its own you may want to add it to your Dock You now have everything you need to program for t
12. chy They re a fraction of what s available THE NS CLASSES The NS classes come from Core Services Foundation framework the Cocoa equiva lent of the Core Foundation framework which contains a huge number of funda mental data types and other objects You should use the fundamental Cocoa classes like NSString and NSArray when ever you can rather than C fundamentals like char or a plain array This is because they tend to play nicely with each other and with the UIKit frameworks and there fore you re less likely to encounter bizarre errors They also follow the memory management rules of Objective C reference counting Although it isn t shown NSNumber is another class you should be aware of Although it shouldn t be used in place of an ordinary number it serves as a great wrapper when you need a number expressed as an object This is useful for sending numbers via message passing NSNumber is capable of holding many sorts of numerical values from floats to integers and more NSObject NSIndexPath NSString UlViewController NSArray UlResponder UlView UlApplication UIControl UIScrollView UlTableView Figure 14 5 This hierarchy graph shows a small selection of the classes UlButton UlSlider available in iOS NSSet NSDictionary 10 1 4 3 CHAPTER 1 Introducing iOS 4 with iPhone and iPad The objects that can hold coll
13. e element Pinch Gesture Move fingers in relation to each other Zooms in or out Tap Touch A single tap Selects an item or engages an action such as a button or link Tap double Touch A double tap Zooms a column When you re designing with the SDK many of the nuances of finger mousing are taken care of for you Standard controls are optimized for finger use and you have access only to the events that work on the iPhone or iPad Chapter 6 explains how to use touches events and actions in iOS as an iOS developer you ll need to change your way of thinking about input to better support the new devices Getting ready for the SDK The iOS software development kit SDK is a suite of programs available in one gar gantuan at the time of writing over 4 GB download from Apple It gives you the tools you need to program Xcode Xcode 4 is the version of the iDE used in this book debug Instruments and test Simulator your iPhone iPod Touch and iPad code NOTE You must have an Intel based Apple Macintosh running Mac OS X 10 6 5 or higher to use the SDK Installing the SDK To obtain the SDK download it from Apple s iOS Dev Center which at the time of this writing is accessible at http developer apple com devcenter ios You ll need to register as an iOS Developer in order to get there but it s a fairly painless process Note that you can also use this site to access Apple documentation and sample source code N
14. ections of values like NSArray a numerical array and NSDictionary an associative array are picky about your sticking to their NS brethren You ll need to wrap C variables inside Cocoa classes whenever you hand off objects to these arrays Finally though NSString can take many sorts of objects when you re formatting a string you should be aware that Cocoa objects may require a dif ferent formatting string than their C equivalents In two situations you ll find that these NS classes can be a deficit First if you re using the Core Foundation framework you ll often have to take advantage of toll free bridging by casting variables as you ll see starting in chapter 9 when we look at the Address Book Second if you re using external APIs you may need to convert some classes into their C equivalents Chapter 9 s look at the SQLite API explores this possi bility with NSString objects often being converted to their UTF 8 equivalent The most important of Cocoa s Foundation objects is NSObject which contains a lot of default behavior including methods for object creation and memory manage ment you ll learn about these later in this chapter THE UI CLASSES The second broad category contains the UI classes These come from Cocoa Touch s UIKit framework which includes all the graphical objects you ll be using as well as all the functionality for the 10S s event model much of which appears in UIResponder That s another topic we
15. ful of information such as the table view controller whereas advanced view controllers let a user move around among several subviews such as the navigation bar controller and the tab bar controller 15 1 5 1 iOS s methods 11 Windows views and view controllers are ultimately part of a view hierarchy This is a tree of objects that begins with the window at its root A simple program may have a window with a view under it Most programs start with a window and have a view con troller under that perhaps supported by additional view controllers each of which controls views that may have their own subviews We ll illustrate this concept more clearly in chapter 5 when we start looking at the basic view controllers that make this sort of hierarchy possible iOS s methods As you ve seen iOS has a complex and deep structure of classes In this section we look at object creation memory management event response and lifecycle management Two of the most important classes are NSObject and UIResponder which contain many of the methods and properties you ll use throughout your programming Thanks to inheritance these important functions and others can be used by many different iOS objects We cover some of these foundational methods here to provide a single reference for their usage but we ll be sure to point them out again when you encounter them for the first time in future chapters Object creation We talked earlier abo
16. g element of the touchscreen is shown off by the fact that a fin ger isnt necessarily singular Recall that the iPhone and iPad touchscreens are multi touch This allows users to manipulate the device with multifinger gestures Pinch zooming is one such example To zoom into a page you tap two fingers on the page and then push them apart to zoom out you similarly push them together Finally a finger isn t persistent A mouse pointer is always on the display but the same isn t true for a finger which can tap here and there without going anywhere in between As you ll see this causes issues with some traditional web techniques that depend on a mouse pointer moving across the screen It also provides limitations that may be seen throughout SDK programs For example there s no standard for cut and paste a ubiquitous feature for any computer produced in the last couple of decades In addition to some changes to existing interfaces the input interface introduces a number of new touches one fingered input and gestures two fingered input as described in table 1 1 13 13 1 CHAPTER 1 Introducing iOS 4 with iPhone and iPad Table 1 1 iPhone and iPad touches and gestures allow you to accept user input in new ways Input Type Summary Bubble Touch Touch and hold Pops up an info bubble on clickable elements Flick Touch Touch and flick Scrolls the page Flick two finger Gesture Touch and flick with two fingers Scrolls the scrollabl
17. he iOS devices but you won t be able to release iPhone or iPad programs on your own that takes a special certifi cate from Apple See appendix C for complete information on this process which is critical for moving your programs from the Simulator onto a real device The Simula tor turns out to be one of several programs you ve installed each of which can be use ful in SDK programming The anatomy of the SDK Xcode Instruments and Dashcode were all available as part of the development library of Mac OS X before the iPhone came along Many of these programs are expanded and revised for use on the iPhone so we ve opted to briefly summarize them all in decreasing order of importance to an SDK developer Xcode 4 is the core of the SDK s integrated development environment IDE It s where you ll set up projects write code in a text editor compile code and gen erally manage your applications It supports code written in Objective C a superset of C that we ll cover in more depth in the next chapter and can also parse C code Interface Builder is now a part of Xcode 4 and it allows you to put together the graphical elements of your program including windows and menus via a quick reliable method You ll learn the specifics of how to use Xcode 4 in chapters 3 and 4 OS Simulator allows you to view an iPhone or iPad screen on your desktop It s a great help for debugging web pages It s an even bigger help when you
18. he iPad or the iPhone with little adaptation iPhone applications are fully compatible on the iPad as is uni versal applications support different experiences depending on the platform they re being run on One more thing iOS 4 3 allows applications to support printing through Airprint Imagine that you can edit your photo with the iPad or iPhone and tap the Print but ton to get the photo printed out on your wi fi printer We ll cover this function in detail later in chapter 11 Understanding iPhone and iPad touch interaction The iPhone and iPad use a multitouch capable capacitive touchscreen Users access the device by tapping around with their finger But a finger isn t a mouse Generally a finger is larger and less accurate than a more traditional pointing device This disal lows certain traditional types of UI that depend on precise selection For example the iPhone and iPad don t have scrollbars Selecting a scrollbar with a fat finger would either be an exercise in frustration or require a huge scrollbar that would take up a lot of the iPhone s precious screen real estate Apple solved this problem by allowing Understanding iPhone and iPad touch interaction 3 Figure 1 1 The iPad and iPhone side by side The primary difference between the two the available screen real estate is readily apparent users to tap anywhere on an iPhone screen and then flick in a specific direction to cause scrolling Another interestin
19. history on iOS The iOS SDK was first introduced in 2007 and released in March of 2008 The third major release iOS 3 0 was released in 2009 Prior to iOS 4 2 there was a short fragmented OS history on the iPhone and iPad the iPhone was running on iOS 4 0 and the iPad was on iOS 3 2 With the new iOS all the iOS powered devices can once again run the same OS For developers the experience for application development is a lot smoother and easier The most prominent feature on iOS 4 is that iOS supports multitasking services including playing audio push noti fications receiving location change events and fast app switching We ll cover the details later in this book The social experience is emphasized on iOS 4 with Game Center and iTunes 10 with Ping Game Center allows developers to create social game experiences with the Game Kit framework For end users it s amazing to start multiplayer games through automatching tracking their achievements and so on There are differences in developing applications for the iPad as opposed to the iPhone but they re primarily related to the varying amount of real estate available to each device as illustrated in figure 1 1 Obviously the iPad has a much bigger screen for display or interaction The content focus is to provide a rich information presenta tion In the UI design you may want to distinguish the iPad from the iPhone For the most part you can run the examples in this book on either t
20. iPad THE ARGUMENTATIVE ALTERNATIVE Sometimes you ll want to send an argument with an init You can do so with an ini tialization function that you name using the format initWithArgument argument Other than the fact that you re sending it an argument it works exactly like a bare init Here s another example drawn from code you ll see in upcoming chapters UITextView alloc initWithFrame textFieldFrame Initialization methods with arguments allow you to create nonstandard objects set up in ways that you choose They re common in UIKit One initialization method with an argument deserves a bit of extra mention init WithCoder is a special initialization method that s called whenever you create an object with Interface Builder and important if you want to do setup for such objects We ll return to Interface Builder in chapter 3 THE FACTORY METHOD ALTERNATIVE A final sort of init supported through iOS is the factory method class method This is a one step message that takes care of both the memory allocation and initialization for you All factory methods are named with the format objecttypeWithArgument argument Here s another real example UIButton buttonWithType UIButtonTypeRoundedRect Class or factory methods make messaging a little clearer They also have the advan tage of handling some memory management which is the topic of the next major cat egory of iOS methods OBJECT CREATION WRAP UP We
21. is book will be built solely using Cocoa Touch But you ll sometimes have to fall back on libraries that are instead based on simple C functionality Examples include Apple s Quartz 2D and Address Book frameworks as well as third party libraries like SQLite Expect object creation memory manage ment and even variable creation to work differently for these non Cocoa libraries 1 4 2 Introducing iOS 9 When you fall back on non Cocoa libraries you ll sometimes have to use Apple s Core Foundation framework which lies below Cocoa Your first encounter with Core Foundation will be when we discuss the Address Book framework in chapter 9 we ll provide more details about how to use Core Foundation at that point Although Core Foundation and Cocoa are distinct classes of frameworks many of their common variable types are toll free bridged which means they can be used inter changeably as long as you cast them For example CFStringRef and NSString are toll free bridged as you ll see when we talk about the Address Book The Apple class references usually point out this toll free bridging for you The object hierarchy of iOS Within these frameworks you can access an immense wealth of classes arranged in a huge hierarchy You ll see many of these used throughout this book and you ll find a listing of even more in appendix A Figure 1 5 shows many of the classes that you ll use over the next several chapters arranged in a hierar
22. ne some of the basics of iOS ane T HelloWorld HelloWorldAppDelegate m gt M HelloWorid iP 4 3 Simu e m HelloworidAcsDelepate m No Seiecton Figure 1 3 The SDK includes Xcode top and two instances of the iOS Simulator running in iPad mode bottom left and iPhone mode right 1 4 1 4 1 CHAPTER 1 Introducing iOS 4 with iPhone and iPad Introducing iOS Apple s iOS SDK provides you with a vast library of objects arranged into several frameworks As a result you ll spend a lot more time sending messages to objects that are ready made for your use than creating new ones Let s begin our look at iOS by exploring several of these objects and how they re arranged We ll take a tour of the anatomy of iOS at how the object hierarchy is arranged and how iOS handles win dows and views The anatomy of iOS i0S s frameworks are divided into four major layers as shown in figure 1 4 Each of these layers contains a variety of frameworks that m you can access when writing iOS SDK programs Generally Soco lough you should prefer the higher level layers when you re cod nig l ing those shown toward the top in the diagram u Cocoa Touch is the framework that you ll become most Core Services familiar with It contains the UIKit framework which is gt what we spend most of our time on in this book and the cores Address Book UI framework UIKit includes window sup Figure 1 4 Apple pro
23. on with iOS s hardware framework access iOS frameworks for these hardware accesses can be found in this book UTILITY APPLICATIONS The key to a successful utility application is to keep it simple Make sure your applica tion will focus on one major task and stick with it The calculator application on iPhone is a good example For a beginner this is a relatively easy category Moreover it fits the needs for the creative idea or the niche market With the knowledge acquired in the first seven chapters of this book you ll be able to create a decent util ity application Next we ll cover the business model for the iOS platform Making money with your application Generally speaking there are three ways to generate profit on the iOS platform Submit a paid application You can price your application at the level you re happy with the current price tier allowed on the App Store is from US 0 99 to US 999 99 there are similar pricing tiers for each App Store market in local cur rencies It should be mentioned that you have a 30 profit share with Apple Submit a free application with in app purchase You can use Store Kit on iOS to gen erate profit through an in app purchase For details please refer to chapter 19 You share 30 of all revenue through in app purchases with Apple Submit a free application supported by advertisements This is a common business model for free applications Follow the step by step instructions on i
24. ould probably back up and explain the underlying way that iOS manages memory objects It does so by maintaining a count of object usage By default it s set to 1 Each retain message increases that count by 1 and each release message reduces that count by 1 When the count drops to 0 the memory for the object is freed up 14 15 3 CHAPTER 1 Introducing iOS 4 with iPhone and iPad Therefore all memory management can be thought of as pairs of messages If you balance every alloc and every retain with a release your object will eventually be freed up when you ve finished with it WARNING Memory management can be the root cause of the bugs Instru ments is a good tool for attempting to diagnose issues with memory leaks Whenever you use the keyword retain or alloc make sure to release If the object is already released don t try to access the released object A good habit would be to assign nil to a released object and check the value isn t nil before accessing the object MEMORY MANAGEMENT WRAP UP Table 1 3 provides a quick summary of the methods we ve looked at to manage the memory used by your objects Table 1 3 The memory management methods help you keep track of the memory you re using and clean it up when you re finished Method Summary alloc Part of the object creation routine that allocates the memory for an object s usage autorelease Request to reduce an object s memory count by 1 when it goes out of scope
25. re considered to own the memory for an object if you created it using a method that contains alloc new copy or mutableCopy You can free memory for an object using the release message as mentioned earlier however an easier way in gen eral is making use of the wonders of autorelease Factory methods like UIButton s buttonWithType return objects that are already autoreleased so you don t need to manage their memory unless you explicitly retain it THE AUTORELEASE ALTERNATIVE If you re responsible for the creation of an object and you re going to pass it off to some other class for usage you should autorelease the object before you send it off This is done with the autorelease method object autorelease You ll typically send the autorelease message just before you return the object at the end of a method After an object has been autoreleased it s watched over by a special NSAutoreleasePool The object is kept alive for the scope of the method to which it s been passed and then the NSAutoreleasePool cleans it up RETAINING AND COUNTING What if you want to hold onto an object that has been passed to you and that will be autoreleased In that case you send it a retain message object retain When you do this you re saying you want the object to stay around but now you ve become responsible for its memory as well you must send a release message at some point to balance your retain At this point we sh
26. rience It s one of the rare technologies that s so intuitive that even a toddler can use it without a user manual iOS provides a whole platform for developers It comes with a huge global market and one integrated distribution place the App Store The iOS SDK offers a rich set of APIs for developers to turn their best ideas into killer applications The new enhancements in iOS 4 allow developers to create applications faster and easier In this chapter we ll first introduce iOS 4 and then go over the key specifica tions of the iPhone iPad and iPod Touch We ll cover the anatomy of iOS includ ing frameworks windows views and methods We ll also cover events memory management and lifecycle management before providing tips on creating a suc cessful application Let s start the story with the iOS platform 1 1 1 2 CHAPTER 1 Introducing iOS 4 with iPhone and iPad All for one and one for all the iOS platform The iPod Touch iPhone and iPad and likely future generations of Apple devices all use iOS 4 3 1 at the time of writing The iOS moniker may be a bit confusing at first but having one OS for all these devices makes it an easy and rewarding platform on which to develop Learn how to develop for it once using the iOS SDK and you can adapt your applications to whichever devices you like For example you can deter mine that the application will support only the devices with GPS or camera Let s review a bit of
27. rom Balsamiq That s it The last step is to learn Objective C by reading this book and build your application with the i0S SDK With this goal in mind let s move on to the application concept What s the category for your application Knowing the category your application fits into will help you make a better estimate of how difficult it will be to build which will help you plan your release date Let s review the most common app categories GAMES AND ENTERTAINMENT This category is hot and crowded It s super competitive to create a successful applica tion under games or entertainment A game or entertainment application generally is heavy on media As a developer you should consider working with a UI designer in order to take advantage of the awesome graphic display quality of the iPhone and iPad Generally speaking a game application may combine the use of the accelerometer drawing and animations audio and Game Kit Once you re familiar with the 10S SDK basics you can jump to later chapters that will cover the iOS frameworks in detail Chapter 15 provides complete coverage of game application development The difficulty level for a developer of game applications is higher compared to other categories Fortunately the rich UI tools on iOS provide a decent fast prototyp ing environment for game developers RICH CONTENT APPLICATIONS Rich content applications are commonly data oriented for instance a Twitter appli ca
28. te for other methods you may want to respond to when writing programs With that we ve completed our look at the big picture methods of 10S You ve not yet seen them in real use so bookmark these pages we ll refer to them when you begin programming in chapter 3 1 6 Howto make an application from an idea At the beginning of this chapter we talked about turning great idea in to a killer appli cation How do you do it Let s walk through the general steps to help make your dreams come true 1 6 1 1 6 2 How to make an application from an idea 17 The chechlist There are several ways to build a universal application running on both the iPhone and iPad Let s start with a handy checklist If you ve already installed the Xcode and iOS SDK as demonstrated earlier in this chapter you ve finished half of the task 1 Join Apple s iOS Developer Program US 99 year will give you access to submit applications to the App Store 2 Have access to an Intel based Mac computer with Mac OS X 10 6 or above 3 Geta good book for beginners this book for example 4 Geta test device iPhone iPod touch or iPad It will be mainly for testing dur ing application development If you re on a tight budget and don t already own one of these devices you don t have to purchase one There are test device ser vices that provide rental equipment 5 Geta sketchbook for the UI design or make use of UI mocking software such as that f
29. tion To allow user access data from the cloud rich content applications provide organized data on the client side On the iPhone the challenge of this rich content application is the limited screen real estate The key to success therefore is in presenting the user with a good amount of well organized data 18 16 3 CHAPTER 1 Introducing iOS 4 with iPhone and iPad On the iPad the focus is to provide rich content on one screen The iPad screen can be compared to a book With a detail oriented UI design you can add plenty of realism to your application For example the page flipping animation in an iBook application allows users to flip through a digital book as if it were a traditional paper book This type of application needs to download data from the server and then store the data locally Chapters 8 and 9 provide a great introduction on how to store data locally on the iPhone and iPad Chapter 14 demos how to fetch data through Internet proto cols on iOS NAVIGATION AND TRAVEL APPLICATIONS This category makes more sense on the iPhone compared to the iPad With its built in GPS and compass the iPhone can be used to provide the user s current location on the fly If you re thinking about presenting Map View on the screen don t miss out on chapter 18 which covers the details on i0S s Map Kit framework With the combination of an accelerometer GPS chip and camera you can build an augmented reality navigation applicati
30. tion you need to write a large variety of iOS applications Glenn Stokol Oracle Corporation The ideal quick start to programming Apple s mobile devices Jonas Bandi TechTalk A no nonsense approach to writing apps for iOS 4 David Sinclair Digital Innovators Take an Apple byte and start coding Jeroen Benckhuijsen Salves Development ISBN 13 978 1 61729 001 5 ISBN 10 1 61729 001 9 7 81617 290015 7 54499
31. troyed starting with your application With multitasking enabled in iOS 4 you can create custom behavior before or after your application enters back ground mode We ll cover more details on this topic in chapter 21 Table 1 4 summarizes some of the important messages that will be sent as part of the lifecycle of your program To respond to them you fill in the contents of the appropriate methods in either an object or its delegate which requires writing a sub class and is one of the prime reasons to do so Table 1 4 Several important methods let you respond to the lifecycle of your application or its individual objects Method Object Summary application DidFinishLaunching UIApplicationDelegate Application has loaded You WithOptions should create initial win dows and otherwise start your program applicationDidReceiveMemoryWarning UIApplicationDelegate Application received a low memory warning You should free up memory applicationWillTerminate UIApplicationDelegate Application is about to end You should free up memory and save state init NSObject Object is being created You should initialize it here dealloc NSObject Object is freeing up its mem ory You should release any objects that haven t been autoreleased Note that we ve included init here because it forms a natural part of the object life cycle You should look at the individual Apple class references particularly UIApplicationDelega
32. ut how to define classes but as we said at the time the specifics of how instance objects are created from classes depend on the implementation of your framework In iOS the NSObject class defines how object creation works You ll meet a few different interfaces that are used to support object creation but they all ultimately fall back to a two step procedure that uses the alloc class method and the init instance method The alloc method allocates the memory for your object and returns the object itself The init method then sets some initial variables in that method They usually occur through a single nested message id newObject objectClass alloc init The alloc method from NSObject should always do the right thing for you But when you write a new subclass you ll almost always want to write a new init method because that s where you define the variables that make your class what it is Here s a default setup for an init which would appear as part of your implementation id init if self super init Instance variables go here a self This code shows all the usual requirements ofan init method First it calls its parent to engage in its class s initialization Then it sets any instance variables that should be set Last it returns the object usually with return self The bare init is one of a few major ways you can create objects in iOS 12 Table 1 2 CuaPTER 1 Introducing iOS 4 with iPhone and
33. ve summarized the four major ways that iOS supports the creation of objects in table 1 2 As witnessed by the examples you ll use all these methods as you move through the upcoming chapters iOS supports several methods that you can use to create objects Different methods are supported by different classes Method Code Summary Simple object alloc init Plain initialization Argument object alloc initWithArgument argument An initialization where one or more Coder Factory arguments is passed to the method object alloc initWithCoder decoder An initialization with an argument used for Interface Builder objects object objecttypeWithArgument argument A one step initialization process with an argument 1 5 2 iOS s methods 13 Memory management Because of power considerations 10S doesn t support garbage collection That means every object that s created must eventually have its memory released by hand at least if you don t want to introduce a memory leak into your program The fundamental rule of memory management in iOS is this if you allocate mem ory for an object you must release it This is done via the release message which is once again inherited from NSObject object release Send that message when you ve finished using an object and you ve done your proper duty as a programmer Note that we said you must release the memory only if you allocated the memory for it You a
34. vides you with four layers of frameworks to use when writing iOS programs port event support and user interface management and it lets you display both text and web pages It further acts as your interface to the accelerometers the camera the photo library and device specific information Media is where you can get access to the major audio and video protocols built into the iPhone and iPad Its four graphical technologies are OpenGL ES EAGL which connects OpenGL to your native window objects Quartz which is Apple s vector based drawing engine and Core Animation which is also built on Quartz Other frameworks of note include Core Audio Open Audio Library and Media Player Core Services offers the frameworks used in all applications Many of them are data related such as the internal Address Book framework Core Services also contains the critical Foundation framework which includes the core definitions of Apple s object oriented data types such as its arrays and sets Core OS includes kernel level software You can access threading files networking other low level I O and memory functions Most of your programming work will be done using the UIKit UI or Foundation NS framework These libraries are collectively called Cocoa Touch they re built on Apple s modern Cocoa framework which is almost entirely object oriented and in our opinion much easier to use than older libraries The vast majority of code in th
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