Objective-C Fundamentals

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Sample application 69 To append one string onto the end of another, you can use the stringByAppending- String: message: NSString *str2 = [str1 stringByAppendingString:@"Cool!"]; This statement appends "Cool!" to the end of str1 and stores the result in str2. You can’t state str2 = str1 + @"Cool!" for reasons that will soon become clear. Now that you know how to create and manipulate string objects, it’s only natural to want to compare one against another to determine if they’re identical. 3.5.4 Comparing strings To compare two string variables against each other, you may come up with a code snippet such as the following based on what you’ve learned about pointers in this chapter: NSString *str1 = [NSString stringWithFormat:@"Hello %@", @"World"]; NSString *str2 = [NSString stringWithFormat:@"Hello %@", @"World"]; if (str1 == str2) { NSLog(@"The two strings are identical"); } Surprisingly, when this code is executed, you’ll notice it indicates that the two freshly created strings aren’t equal! To understand why, you need to realize that the two variables str1 and str2 are both simple C-style pointers. With its C-based roots, the == operator checks for equality by determining if both variables point to the same piece of memory. Because you create two separate string instances, the two pointers point to distinct locations, and the expression evaluates to false. That both strings contain an identical sequence of characters is irrelevant because the == operator only considers the string’s memory location. To work around this problem, <strong>Objective</strong>-C, like most object-oriented languages with pointers, provides a message to compare the contents of an object instead of its location in memory. In <strong>Objective</strong>-C this message is called isEqual: if ([str1 isEqual:str2]) { NSLog(@"The two strings are identical"); } It’s for a similar reason that the + operator can’t be used for string concatenation: it’s already used with C-style pointers for pointer arithmetic. 3.6 Sample application To put the concepts you’ve learned in this chapter into practice, let’s expand the Rental Manager application to make greater use of the services provided by NSString to search and modify string content. Figure 3.5 shows how the application will look once you finish this round of modifications. Each rental property has an image beside it that categorizes the property’s location, such as near the sea, in the city, or in an alpine setting. To display images in your iPhone application, the obvious first step is to include some image resources in your project. To add images to the Xcode project, drag and
70 CHAPTER 3 An introduction to objects Figure 3.5 An updated version of the Rental Manager application. Notice each property has an image beside it indicating the type of geographical location of the property. drop the image files from a Finder window into the Supporting Files group located in Xcode’s project navigator pane. A sheet will appear from which you can select a button labeled Add. For this task, you need to source three images. Details of the images we utilized are listed in table 3.1. You can use a service such as Google Image Search to source your own. Table 3.1 The images used to represent different property locations. Selection of the image for a particular property is based on the city found in its associated address. Some city names that map to each image are provided as examples. Image Filename Example cities sea.png Sumner mountain.png Clifton city.png Riccarton, Christchurch
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Christopher K. Fairbairn Johannes F
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Objective-C Fundamentals CHRISTOPHE
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PART 1 brief contents GETTING START
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viii CONTENTS 1.5 Compiling the Coi
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x CONTENTS 5.4 Declared properties
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xii CONTENTS PART 3 MAKING MAXIMUM
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preface Having been involved in the
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ACKNOWLEDGMENTS xvii Christopher wo
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ABOUT THIS BOOK xix skills. There
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author online Purchase of Objective
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Part 1 Getting started with Objecti
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4 CHAPTER 1 Building your first iOS
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10 CHAPTER 1 Building your first iO
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Page 41 and 42: 18 CHAPTER 1 Building your first iO
Page 51 and 52: Data types, variables, and constant
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Page 79 and 80: 56 CHAPTER 3 An introduction to obj
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Page 97 and 98: Storing data in collections This ch
Page 99 and 100: 76 CHAPTER 4 Storing data in collec
Page 120 and 121: Creating classes This chapter cover
Page 122 and 123: Declaring the interface of a class
Page 130 and 131: Providing an implementation for a c
Page 132 and 133: Declared properties 109 - (Property
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Page 136 and 137: Declared properties 113 Although @s
Page 138 and 139: Creating and destroying objects 115
Page 140 and 141: Creating and destroying objects 117
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Creating and destroying objects 119
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Using the class in the Rental Manag
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Summary 123 a number of rental prop
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Subclassing 125 the only class you
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Adding new instance variables 127 s
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Accessing existing instance variabl
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Overriding methods 131 } return gen
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Overriding methods 133 } "for $%@ p
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Class clusters 135 Figure 6.2 Graph
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Categories 137 This code tells the
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Subclassing in your demo applicatio
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Subclassing in your demo applicatio
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Summary 143 6.8 Summary Object-orie
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Defining a protocol 145 Mastering t
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Implementing a protocol 147 7.2.1 C
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Implementing a protocol 149 Listing
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Important protocols 151 iPhone UIKi
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Important protocols 153 executed. T
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Important protocols 155 Any table v
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Important protocols 157 or in table
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Important protocols 159 For s
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Important protocols 161 Listing 7.1
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Dynamic typing and runtime type inf
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Static vs. dynamic typing 165 If yo
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How messaging works 167 Messages ar
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How messaging works 169 8.3.2 Handl
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Runtime type information 171 The if
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Runtime type information 173 8.4.3
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Practical uses of runtime type intr
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Memory management This chapter cove
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Reference counting 179 Figure 9.1 A
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Reference counting 181 the object i
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Reference counting 183 Keep yoursel
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Autorelease pools 185 Ideally, you
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Autorelease pools 187 With knowledg
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Autorelease pools 189 i * 1000 + j]
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Memory zones 191 Memory zones have
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Responding to low-memory warnings 1
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Summary 199 addObserver:selector:na
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Part 3 Making maximum use of framew
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Error and exception handling This c
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NSError—handling errors the Cocoa
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Creating NSError objects 207 chapte
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Creating NSError objects 209 10.2.2
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Summary 211 10.3.2 Catching excepti
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Making your objects KVC-compliant 2
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Making your objects KVC-compliant 2
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Handling special cases 217 This que
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Filtering and matching with predica
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Sample application 225 rentingFor:2
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Summary 227 The core of the logic o
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Core Data history 229 Structured Qu
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Core Data objects 231 In Xcode you
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Core Data resources 233 careful to
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Building the PocketTasks applicatio
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Beyond the basics 251 How do you us
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Beyond the basics 253 All you do is
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Beyond the basics 255 attributeName
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Blocks and Grand Central Dispatch T
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The syntax of blocks 259 What if yo
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The syntax of blocks 261 change the
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The syntax of blocks 263 } [super d
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Performing work asynchronously 265
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Summary 275 more to learn about GCD
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Building an application, complete w
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Understanding NSLog 279 Figure 14.3
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Bringing memory leaks under control
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Bringing memory leaks under control
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Detecting zombies 285 (and the appl
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Summary 287 and its ease of use and
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Preparing your iOS device for devel
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Preparing your iOS device for devel
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appendix B The basics of C Througho
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Variable naming conventions 295 As
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Expressions 297 Table B.3 Relationa
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Expressions 299 B.2.4 Assignment op
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Conditional statements 301 based on
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Conditional statements 303 The gene
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Looping statements 305 Not as strai
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Looping statements 307 One importan
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Looping statements 309 As in a do l
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Summary 311 CONTINUE The continue s
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A short history of Objective-C 313
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The iPhone SDK: Safari 315 C.2 Alte
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The iPhone SDK: Safari 317 C.3.2 ha
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The iPhone SDK: Safari 319 It’s i
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Scripting languages: Lua and Ruby 3
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Mono (.NET) 323 the iOS platform. F
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Summary 325 Xamarin announced a fol
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index Symbols ^ operator 298 - oper
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INDEX 329 application-specific quer
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INDEX 331 collections (continued) e
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INDEX 333 E e character 35 editButt
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INDEX 335 iOS Developer account 9 i
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INDEX 337 mutableCopyWithZone 190 M
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INDEX 339 Organizer window 291 over
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INDEX 341 setFlag 164 setNilValueFo
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INDEX 343 vardic method 75 variable
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