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iOS 5 Programming Cookbook

Cover of iOS 5 Programming Cookbook by Vandad Nahavandipoor Published by O'Reilly Media, Inc.
  1. iOS 5 Programming Cookbook
    1. SPECIAL OFFER: Upgrade this ebook with O’Reilly
    2. A Note Regarding Supplemental Files
    3. Preface
      1. Audience
      2. Organization of This Book
      3. Additional Resources
      4. Conventions Used in This Book
      5. Using Code Examples
      6. We’d Like to Hear from You
      7. Safari® Books Online
      8. Acknowledgments
    4. 1. The Basics
      1. 1.0. Introduction
      2. 1.1. Creating a Simple iOS App in Xcode
      3. 1.2. Understanding Interface Builder
      4. 1.3. Compiling iOS Apps
      5. 1.4. Running iOS Apps on the Simulator
      6. 1.5. Running iOS Apps on iOS Devices
      7. 1.6. Packaging iOS Apps for Distribution
      8. 1.7. Declaring Variables in Objective-C
      9. 1.8. Allocating and Making Use of Strings
      10. 1.9. Comparing Values in Objective-C with an If Statement
      11. 1.10. Implementing Loops with For Statements
      12. 1.11. Implementing While Loops
      13. 1.12. Creating Custom Classes
      14. 1.13. Defining Functionality for Classes
      15. 1.14. Defining Two or More Methods with the Same Name
      16. 1.15. Allocating and Initializing Objects
      17. 1.16. Adding Properties to Classes
      18. 1.17. Moving From Manual Reference Counting to Automatic Reference Counting
      19. 1.18. Typecasting with Automatic Reference Counting
      20. 1.19. Delegating Tasks with Protocols
      21. 1.20. Determining Whether Instance or Class Methods Are Available
      22. 1.21. Determining Whether a Class Is Available at Runtime
      23. 1.22. Allocating and Making Use of Numbers
      24. 1.23. Allocating and Making Use of Arrays
      25. 1.24. Allocating and Making Use of Dictionaries
      26. 1.25. Allocating and Making Use of Sets
      27. 1.26. Creating Bundles
      28. 1.27. Loading Data From the Main Bundle
      29. 1.28. Loading Data From Other Bundles
      30. 1.29. Sending Notifications with NSNotificationCenter
      31. 1.30. Listening for Notifications Sent From NSNotificationCenter
    5. 2. Implementing Controllers and Views
      1. 2.0. Introduction
      2. 2.1. Displaying Alerts with UIAlertView
      3. 2.2. Creating and Using Switches with UISwitch
      4. 2.3. Picking Values with UIPickerView
      5. 2.4. Picking the Date and Time with UIDatePicker
      6. 2.5. Implementing Range Pickers with UISlider
      7. 2.6. Grouping Compact Options with UISegmentedControl
      8. 2.7. Presenting and Managing Views with UIViewController
      9. 2.8. Implementing Navigation with UINavigationController
      10. 2.9. Manipulating a Navigation Controller’s Array of View Controllers
      11. 2.10. Displaying an Image on a Navigation Bar
      12. 2.11. Adding Buttons to Navigation Bars Using UIBarButtonItem
      13. 2.12. Presenting Multiple View Controllers with UITabBarController
      14. 2.13. Displaying Static Text with UILabel
      15. 2.14. Accepting User Text Input with UITextField
      16. 2.15. Displaying Long Lines of Text with UITextView
      17. 2.16. Adding Buttons to the User Interface with UIButton
      18. 2.17. Displaying Images with UIImageView
      19. 2.18. Creating Scrollable Content with UIScrollView
      20. 2.19. Loading Web Pages with UIWebView
      21. 2.20. Presenting Master-Detail Views with UISplitViewController
      22. 2.21. Enabling Paging with UIPageViewController
      23. 2.22. Displaying Popovers with UIPopoverController
      24. 2.23. Displaying Progress with UIProgressView
      25. 2.24. Listening and Reacting to Keyboard Notifications
    6. 3. Constructing and Using Table Views
      1. 3.0. Introduction
      2. 3.1. Instantiating a Table View
      3. 3.2. Assigning a Delegate to a Table View
      4. 3.3. Populating a Table View with Data
      5. 3.4. Receiving and Handling Table View Events
      6. 3.5. Using Different Types of Accessories in a Table View Cell
      7. 3.6. Creating Custom Table View Cell Accessories
      8. 3.7. Displaying Hierarchical Data in Table Views
      9. 3.8. Enabling Swipe Deletion of Table View Cells
      10. 3.9. Constructing Headers and Footers in Table Views
      11. 3.10. Displaying Context Menus on Table Views Cells
      12. 3.11. Moving Cells and Sections in Table Views
      13. 3.12. Deleting Cells and Sections From Table Views
    7. 4. Storyboards
      1. 4.0. Introduction
      2. 4.1. Creating a Project with Storyboards
      3. 4.2. Adding a Navigation Controller to a Storyboard
      4. 4.3. Passing Data From One Screen to Another
      5. 4.4. Adding a Storyboard to an Existing Project
    8. 5. Concurrency
      1. 5.0. Introduction
      2. 5.1. Constructing Block Objects
      3. 5.2. Accessing Variables in Block Objects
      4. 5.3. Invoking Block Objects
      5. 5.4. Dispatching Tasks to Grand Central Dispatch
      6. 5.5. Performing UI-Related Tasks with GCD
      7. 5.6. Performing Non-UI Related Tasks Synchronously with GCD
      8. 5.7. Performing Non-UI Related Tasks Asynchronously with GCD
      9. 5.8. Performing Tasks After a Delay with GCD
      10. 5.9. Performing a Task Only Once with GCD
      11. 5.10. Grouping Tasks Together with GCD
      12. 5.11. Constructing Your Own Dispatch Queues with GCD
      13. 5.12. Running Tasks Synchronously with Operations
      14. 5.13. Running Tasks Asynchronously with Operations
      15. 5.14. Creating Dependency Between Operations
      16. 5.15. Creating Timers
      17. 5.16. Creating Concurrency with Threads
      18. 5.17. Invoking Background Methods
      19. 5.18. Exiting Threads and Timers
    9. 6. Core Location and Maps
      1. 6.0. Introduction
      2. 6.1. Creating a Map View
      3. 6.2. Handling the Events of a Map View
      4. 6.3. Pinpointing the Location of a Device
      5. 6.4. Displaying Pins on a Map View
      6. 6.5. Displaying Pins with Different Colors on a Map View
      7. 6.6. Displaying Custom Pins on a Map View
      8. 6.7. Converting Meaningful Addresses to Longitude and Latitude
      9. 6.8. Converting Longitude and Latitude to a Meaningful Address
    10. 7. Implementing Gesture Recognizers
      1. 7.0. Introduction
      2. 7.1. Detecting Swipe Gestures
      3. 7.2. Detecting Rotation Gestures
      4. 7.3. Detecting Panning and Dragging Gestures
      5. 7.4. Detecting Long Press Gestures
      6. 7.5. Detecting Tap Gestures
      7. 7.6. Detecting Pinch Gestures
    11. 8. Networking, JSON, XML, and Twitter
      1. 8.0. Introduction
      2. 8.1. Downloading Asynchronously with NSURLConnection
      3. 8.2. Handling Timeouts in Asynchronous Connections
      4. 8.3. Downloading Synchronously with NSURLConnection
      5. 8.4. Modifying a URL Request with NSMutableURLRequest
      6. 8.5. Sending HTTP GET Requests with NSURLConnection
      7. 8.6. Sending HTTP POST Requests with NSURLConnection
      8. 8.7. Sending HTTP DELETE Requests with NSURLConnection
      9. 8.8. Sending HTTP PUT Requests with NSURLConnection
      10. 8.9. Serializing Arrays and Dictionaries into JSON
      11. 8.10. Deserializing JSON into Arrays and Dictionaries
      12. 8.11. Integrating Twitter Functionality into Your Apps
      13. 8.12. Parsing XML with NSXMLParser
    12. 9. Audio and Video
      1. 9.0. Introduction
      2. 9.1. Playing Audio Files
      3. 9.2. Handling Interruptions While Playing Audio
      4. 9.3. Recording Audio
      5. 9.4. Handling Interruptions While Recording Audio
      6. 9.5. Playing Audio Over Other Active Sounds
      7. 9.6. Playing Video Files
      8. 9.7. Capturing Thumbnails From a Video File
      9. 9.8. Accessing the Music Library
    13. 10. Address Book
      1. 10.0. Introduction
      2. 10.1. Retrieving a Reference to an Address Book
      3. 10.2. Retrieving All the People in the Address Book
      4. 10.3. Retrieving Properties of Address Book Entries
      5. 10.4. Inserting a Person Entry into the Address Book
      6. 10.5. Inserting a Group Entry into the Address Book
      7. 10.6. Adding Persons to Groups
      8. 10.7. Searching the Address Book
      9. 10.8. Retrieving and Setting a Person’s Address Book Image
    14. 11. Camera and the Photo Library
      1. 11.0. Introduction
      2. 11.1. Detecting and Probing the Camera
      3. 11.2. Taking Photos with the Camera
      4. 11.3. Taking Videos with the Camera
      5. 11.4. Storing Photos in the Photo Library
      6. 11.5. Storing Videos in the Photo Library
      7. 11.6. Retrieving Photos and Videos From the Photo Library
      8. 11.7. Retrieving Assets From the Assets Library
      9. 11.8. Editing Videos on an iOS Device
    15. 12. Multitasking
      1. 12.0. Introduction
      2. 12.1. Detecting the Availability of Multitasking
      3. 12.2. Completing a Long-Running Task in the Background
      4. 12.3. Receiving Local Notifications in the Background
      5. 12.4. Playing Audio in the Background
      6. 12.5. Handling Location Changes in the Background
      7. 12.6. Saving and Loading the State of Multitasking iOS Apps
      8. 12.7. Handling Network Connections in the Background
      9. 12.8. Handling Notifications Delivered to a Waking App
      10. 12.9. Responding to Changes in App Settings
      11. 12.10. Opting Out of Multitasking
    16. 13. Core Data
      1. 13.0. Introduction
      2. 13.1. Creating a Core Data Model with Xcode
      3. 13.2. Generating Class Files for Core Data Entities
      4. 13.3. Creating and Saving Data Using Core Data
      5. 13.4. Reading Data From Core Data
      6. 13.5. Deleting Data From Core Data
      7. 13.6. Sorting Data in Core Data
      8. 13.7. Boosting Data Access in Table Views
      9. 13.8. Implementing Relationships in Core Data
    17. 14. Dates, Calendars, and Events
      1. 14.0. Introduction
      2. 14.1. Retrieving the List of Calendars
      3. 14.2. Adding Events to Calendars
      4. 14.3. Accessing the Contents of Calendars
      5. 14.4. Removing Events From Calendars
      6. 14.5. Adding Recurring Events to Calendars
      7. 14.6. Retrieving the Attendees of an Event
      8. 14.7. Adding Alarms to Calendars
      9. 14.8. Handling Event Changed Notifications
      10. 14.9. Presenting Event View Controllers
      11. 14.10. Presenting Event Edit View Controllers
    18. 15. Graphics and Animations
      1. 15.0. Introduction
      2. 15.1. Enumerating and Loading Fonts
      3. 15.2. Drawing Text
      4. 15.3. Constructing, Setting, and Using Colors
      5. 15.4. Drawing Images
      6. 15.5. Drawing Lines
      7. 15.6. Constructing Paths
      8. 15.7. Drawing Rectangles
      9. 15.8. Adding Shadows to Shapes
      10. 15.9. Drawing Gradients
      11. 15.10. Displacing Shapes Drawn on Graphic Contexts
      12. 15.11. Scaling Shapes Drawn on Graphic Contexts
      13. 15.12. Rotating Shapes Drawn on Graphic Contexts
      14. 15.13. Animating and Moving Views
      15. 15.14. Animating and Scaling Views
      16. 15.15. Animating and Rotating Views
    19. 16. Core Motion
      1. 16.0. Introduction
      2. 16.1. Detecting the Availability of an Accelerometer
      3. 16.2. Detecting the Availability of a Gyroscope
      4. 16.3. Retrieving Accelerometer Data
      5. 16.4. Detecting Shakes on an iOS Device
      6. 16.5. Retrieving Gyroscope Data
    20. 17. iCloud
      1. 17.0. Introduction
      2. 17.1. Setting Up Your App for iCloud
      3. 17.2. Storing and Synchronizing Dictionaries in iCloud
      4. 17.3. Creating and Managing Folders for Apps in iCloud
      5. 17.4. Searching for Files and Folders in iCloud
      6. 17.5. Storing User Documents in iCloud
      7. 17.6. Managing the State of Documents in iCloud
      8. 17.7. Handling Conflicts in iCloud Documents
    21. Index
    22. About the Author
    23. Colophon
    24. SPECIAL OFFER: Upgrade this ebook with O’Reilly

1.13. Defining Functionality for Classes


You want to define some functionality for your classes and allow them to be reused later.


Create instance or class methods for your classes in order to create reusable blocks of code, or simply call a method in your program.


Nearly every programming language creates procedures and functions to encapsulate specific functionality, especially functionality that the programmer uses over and over. Some languages consider “procedure” and “function” just terms for the same thing, while others make a distinction between them. A procedure is a block of code with a name and an optional set of parameters. It does not have a return value. In Objective-C, a procedure returns void to indicate it does not return a value. A function is similar but does have a return value. Here is a simple procedure (with an empty body) written in C:

void sendEmailTo(const char *paramTo,
                 const char *paramSubject,
                 const char *paramEmailMessage){

  /* send the email here ... */

This procedure is named sendEmailTo and has three parameters: paramTo, paramSubject, and paramEmailMessage. We can then call this procedure as follows:

            "My Subject",
            "Please read my email");

Turning this procedure into a function that returns a Boolean value, we will have code similar to this:

BOOL sendEmailTo(const char *paramTo,
                 const char *paramSubject,
                 const char *paramEmailMessage){

  /* send the email here ... */

  if (paramTo == nil ||
      paramSubject == nil ||
      paramEmailMessage == nil){
    /* One or some of the parameters are nil */
    NSLog(@"Nil parameter(s) is/are provided.");
    return NO;

  return YES;

Calling this function is similar to calling the sendEmailTo procedure except that with a function, we can retrieve the return value, like so:

BOOL isSuccessful = sendEmailTo("",
                                "My Subject",
                                "Please read my email");

if (isSuccessful){
  /* Successfully sent the email */
} else {
  /* Failed to send the email. Perhaps we should display
   an error message to the user */

In Objective-C, each method is created for a class. Creating Objective-C methods is quite different from writing procedures and functions in a programming language such as C. Methods fall into two categories: instance or class. Instance methods are methods that can be called on an instance of the class (that is, on each object you create based on the class), whereas class methods get called on the class itself and do not require an instance of the class to be created by the programmer. To create a method in Objective-C, follow these steps in the .m file of your target class:

  1. Type if you want an instance method or + if you want a class method.

  2. Choose the return type of your method and enclose it within parentheses—for instance, (void) for no return value, (BOOL) for a Boolean value, (NSObject *) to return an instance of NSObject, and so on.

  3. Choose a name for your method. Start the name with a lowercase letter. It is common in Objective-C to start method names with a lowercase letter—for instance, sendEmailTo instead of SendEmailTo.

  4. If you do not want any parameters for your method, jump to step 9.

  5. Choose two names for your parameter. One name becomes a part of the method name and will be used from outside the method (this is optional for all parameters except the first). The other name will be used as a parameter name inside the method. There is an exception to this in which the first name of the first parameter of a method is part of the name of the method that you chose in step 3. For this first parameter, you must only choose a second name, which becomes the parameter name used inside the method itself.

  6. Once you are done choosing the name for your parameter, choose the data type of the method and enclose it within parentheses.

  7. Put a colon after your parameter’s first chosen name (if any), and put the parentheses that carry the data type of your method followed by the second name for your parameter.

  8. Repeat steps 5 through 7 for any other parameters that you might have.

  9. Insert an open curly brace ({) after the method name and parameter names (if you have parameters) and a closing curly brace (}) at the end.

Going back to the sendEmailTo procedure example that we saw earlier, let’s attempt to create the same procedure as a method in Objective-C:

- (BOOL) sendEmailTo:(NSString *)paramTo
         withSubject:(NSString *)paramSubject
     andEmailMessage:(NSString *)paramEmailMessage{

  /* Send the email and return an appropriate value */

  if ([paramTo length] == 0 ||
      [paramSubject length] == 0 ||
      [paramEmailMessage length] == 0){
    /* One or some of the parameters are empty */
    NSLog(@"Empty parameter(s) is/are provided.");
    return NO;

  return YES;


This is an instance method (-) that returns a Boolean value (BOOL). The name of this method is sendEmailTo:withSubject:andEmailMessage: and it has three parameters. We can then call this method in this way:

[self sendEmailTo:@""
      withSubject:@"My Subject"
  andEmailMessage:@"Please read my email."];

As mentioned previously, the first name of every parameter (except the first) is optional. In other words, we can construct the sendEmailTo:withSubject:andEmailMessage: method in another way with a different name:

- (BOOL) sendEmailTo:(NSString *)paramTo
                    :(NSString *)paramSubject
                    :(NSString *)paramEmailMessage{

  /* Send the email and return an appropriate value */

  if (paramTo length] == 0 ||
      [paramSubject length] == 0 ||
      [paramEmailMessage length] == 0){
    NSLog(@"Empty parameter(s) is/are provided.");
    return NO;

  return YES;



I heavily discourage you from writing methods that have no external names for their parameters. This is indeed a very bad programming practice and will confuse you and those who you work with in the same team, regardless of how well you might have documented your code.

We can call this method like so:

[self sendEmailTo:@""
                 :@"My Subject"
                 :@"Please read my email."];

As you can see, the first implementation is easier to understand when you look at the invocation, since you can see the name of each parameter in the call itself.

Declaring and implementing a class method is similar to declaring and implementing an instance method. Here are a couple of things you have to keep in mind when declaring and implementing a class method:

  • The method type identifier of a class method is + instead of the - type identifier for instance methods.

  • You can access self in a class method.

  • Class methods are useful when you want to provide new methods of instantiation for your classes. For example, a class method named allocAndInit could both allocate and initialize an object and return the object to its caller.

Suppose we want to create a class named MyClass. In this class, we want to implement a class method named allocAndInit that will allocate and initialize an instance of MyClass and return the result to the caller. The header file of this class will look like this:

#import <Foundation/Foundation.h>

@interface MyClass : NSObject

+ (id) allocAndInit;


The implementation of this class method will be very straightforward. A simple allocation followed by an initialization:

#import "MyClass.h"

@implementation MyClass

+ (id) allocAndInit{
  MyClass *result = [[MyClass alloc] init];
  return result;


In our app delegate now we can use this class method to allocate and initialize an instance of MyClass, like so:

#import "AppDelegate.h"
#import "MyClass.h"

@implementation AppDelegate

@synthesize window = _window;

- (BOOL)            application:(UIApplication *)application
  didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{

  MyClass *instance1 = [MyClass allocAndInit];
  NSLog(@"Instance 1 = %@", instance1);

  self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
  self.window.backgroundColor = [UIColor whiteColor];
  [self.window makeKeyAndVisible];
  return YES;

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