You are previewing iOS 6 Programming Cookbook.

iOS 6 Programming Cookbook

Cover of iOS 6 Programming Cookbook by Vandad Nahavandipoor Published by O'Reilly Media, Inc.
  1. iOS 6 Programming Cookbook
  2. 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
  3. 1. The Basics
    1. 1.0. Introduction
    2. 1.1. Creating a Simple iOS App in Xcode
      1. Problem
      2. Solution
      3. Discussion
    3. 1.2. Understanding Interface Builder
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 1.3. Compiling iOS Apps
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 1.4. Running iOS Apps on the Simulator
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 1.5. Running iOS Apps on iOS Devices
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    7. 1.6. Packaging iOS Apps for Distribution
      1. Problem
      2. Solution
      3. Discussion
    8. 1.7. Declaring Variables in Objective-C
      1. Problem
      2. Solution
      3. Discussion
    9. 1.8. Allocating and Making Use of Strings
      1. Problem
      2. Solution
      3. Discussion
    10. 1.9. Comparing Values in Objective-C with an if Statement
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    11. 1.10. Implementing Loops with for Statements
      1. Problem
      2. Solution
      3. Discussion
    12. 1.11. Implementing while Loops
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    13. 1.12. Creating Custom Classes
      1. Problem
      2. Solution
      3. Discussion
    14. 1.13. Defining Functionality for Classes
      1. Problem
      2. Solution
      3. Discussion
    15. 1.14. Defining Two or More Methods with the Same Name
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    16. 1.15. Allocating and Initializing Objects
      1. Problem
      2. Solution
      3. Discussion
    17. 1.16. Adding Properties to Classes
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    18. 1.17. Moving from Manual Reference Counting to Automatic Reference Counting
      1. Problem
      2. Solution
      3. Discussion
    19. 1.18. Typecasting with Automatic Reference Counting
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    20. 1.19. Delegating Tasks with Protocols
      1. Problem
      2. Solution
      3. Discussion
    21. 1.20. Determining Whether Instance or Class Methods Are Available
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    22. 1.21. Determining Whether a Class Is Available at Runtime
      1. Problem
      2. Solution
      3. Discussion
    23. 1.22. Allocating and Making Use of Numbers
      1. Problem
      2. Solution
      3. Discussion
    24. 1.23. Allocating and Making Use of Arrays
      1. Problem
      2. Solution
      3. Discussion
    25. 1.24. Allocating and Making Use of Dictionaries
      1. Problem
      2. Solution
      3. Discussion
    26. 1.25. Allocating and Making Use of Sets
      1. Problem
      2. Solution
      3. Discussion
    27. 1.26. Creating Bundles
      1. Problem
      2. Solution
      3. Discussion
    28. 1.27. Loading Data from the Main Bundle
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    29. 1.28. Loading Data from Other Bundles
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    30. 1.29. Sending Notifications with NSNotificationCenter
      1. Problem
      2. Solution
      3. Discussion
    31. 1.30. Listening for Notifications Sent from NSNotificationCenter
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  4. 2. Implementing Controllers and Views
    1. 2.0. Introduction
    2. 2.1. Displaying Alerts with UIAlertView
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 2.2. Creating and Using Switches with UISwitch
      1. Problem
      2. Solution
      3. Discussion
    4. 2.3. Customizing the UISwitch
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 2.4. Picking Values with UIPickerView
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 2.5. Picking the Date and Time with UIDatePicker
      1. Problem
      2. Solution
      3. Discussion
    7. 2.6. Implementing Range Pickers with UISlider
      1. Problem
      2. Solution
      3. Discussion
    8. 2.7. Customizing the UISlider
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 2.8. Grouping Compact Options with UISegmentedControl
      1. Problem
      2. Solution
      3. Discussion
    10. 2.9. Customizing the UISegmentedControl
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    11. 2.10. Presenting and Managing Views with UIViewController
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. 2.11. Presenting Sharing Options with UIActivityViewController
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    13. 2.12. Implementing Navigation with UINavigationController
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    14. 2.13. Manipulating a Navigation Controller’s Array of View Controllers
      1. Problem
      2. Solution
      3. Discussion
    15. 2.14. Displaying an Image on a Navigation Bar
      1. Problem
      2. Solution
      3. Discussion
    16. 2.15. Adding Buttons to Navigation Bars Using UIBarButtonItem
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    17. 2.16. Presenting Multiple View Controllers with UITabBarController
      1. Problem
      2. Solution
      3. Discussion
    18. 2.17. Displaying Static Text with UILabel
      1. Problem
      2. Solution
      3. Discussion
    19. 2.18. Customizing the UILabel
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    20. 2.19. Accepting User Text Input with UITextField
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    21. 2.20. Displaying Long Lines of Text with UITextView
      1. Problem
      2. Solution
      3. Discussion
    22. 2.21. Adding Buttons to the User Interface with UIButton
      1. Problem
      2. Solution
      3. Discussion
    23. 2.22. Displaying Images with UIImageView
      1. Problem
      2. Solution
      3. Discussion
    24. 2.23. Creating Scrollable Content with UIScrollView
      1. Problem
      2. Solution
      3. Discussion
    25. 2.24. Loading Web Pages with UIWebView
      1. Problem
      2. Solution
      3. Discussion
    26. 2.25. Presenting Master-Detail Views with UISplitViewController
      1. Problem
      2. Solution
      3. Discussion
    27. 2.26. Enabling Paging with UIPageViewController
      1. Problem
      2. Solution
      3. Discussion
    28. 2.27. Displaying Popovers with UIPopoverController
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    29. 2.28. Displaying Progress with UIProgressView
      1. Problem
      2. Solution
      3. Discussion
    30. 2.29. Listening and Reacting to Keyboard Notifications
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    31. 2.30. Constructing and Displaying Styled Texts
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  5. 3. Auto Layout and the Visual Format Language
    1. 3.0. Introduction
    2. 3.1. Placing UI Components in the Center of the Screen
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 3.2. Defining Horizontal and Vertical Constraints with the Visual Format Language
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 3.3. Utilizing Cross View Constraints
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 3.4. Configuring Auto Layout Constraints in Interface Builder
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  6. 4. Constructing and Using Table Views
    1. 4.0. Introduction
    2. 4.1. Instantiating a Table View
      1. Problem
      2. Solution
      3. Discussion
    3. 4.2. Assigning a Delegate to a Table View
      1. Problem
      2. Solution
      3. Discussion
    4. 4.3. Populating a Table View with Data
      1. Problem
      2. Solution
      3. Discussion
    5. 4.4. Receiving and Handling Table View Events
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 4.5. Using Different Types of Accessories in a Table View Cell
      1. Problem
      2. Solution
      3. Discussion
    7. 4.6. Creating Custom Table View Cell Accessories
      1. Problem
      2. Solution
      3. Discussion
    8. 4.7. Displaying Hierarchical Data in Table Views
      1. Problem
      2. Solution
      3. Discussion
    9. 4.8. Enabling Swipe Deletion of Table View Cells
      1. Problem
      2. Solution
      3. Discussion
    10. 4.9. Constructing Headers and Footers in Table Views
      1. Problem
      2. Solution
      3. Discussion
    11. 4.10. Displaying Context Menus on Table View Cells
      1. Problem
      2. Solution
      3. Discussion
    12. 4.11. Moving Cells and Sections in Table Views
      1. Problem
      2. Solution
      3. Discussion
    13. 4.12. Deleting Cells and Sections from Table Views
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    14. 4.13. Utilizing the UITableViewController for Easy Creation of Table Views
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    15. 4.14. Displaying a Refresh Control for Table Views
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  7. 5. Storyboards
    1. 5.0. Introduction
    2. 5.1. Creating a Project with Storyboards
      1. Problem
      2. Solution
      3. Discussion
    3. 5.2. Adding a Navigation Controller to a Storyboard
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 5.3. Passing Data From One Screen to Another
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 5.4. Adding a Storyboard to an Existing Project
      1. Problem
      2. Solution
      3. Discussion
  8. 6. Concurrency
    1. 6.0. Introduction
    2. 6.1. Constructing Block Objects
      1. Problem
      2. Solution
      3. Discussion
    3. 6.2. Accessing Variables in Block Objects
      1. Problem
      2. Solution
      3. Discussion
    4. 6.3. Invoking Block Objects
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 6.4. Dispatching Tasks to Grand Central Dispatch
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 6.5. Performing UI-Related Tasks with GCD
      1. Problem
      2. Solution
      3. Discussion
    7. 6.6. Executing Non-UI Related Tasks Synchronously with GCD
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 6.7. Executing Non-UI Related Tasks Asynchronously with GCD
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 6.8. Performing Tasks After a Delay with GCD
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    10. 6.9. Performing a Task Only Once with GCD
      1. Problem
      2. Solution
      3. Discussion
    11. 6.10. Grouping Tasks Together with GCD
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. 6.11. Constructing Your Own Dispatch Queues with GCD
      1. Problem
      2. Solution
      3. Discussion
    13. 6.12. Running Tasks Synchronously with Operations
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    14. 6.13. Running Tasks Asynchronously with Operations
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    15. 6.14. Creating Dependency Between Operations
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    16. 6.15. Creating Timers
      1. Problem
      2. Solution
      3. Discussion
    17. 6.16. Creating Concurrency with Threads
      1. Problem
      2. Solution
      3. Discussion
    18. 6.17. Invoking Background Methods
      1. Problem
      2. Solution
      3. Discussion
    19. 6.18. Exiting Threads and Timers
      1. Problem
      2. Solution
      3. Discussion
  9. 7. Core Location and Maps
    1. 7.0. Introduction
    2. 7.1. Creating a Map View
      1. Problem
      2. Solution
      3. Discussion
    3. 7.2. Handling the Events of a Map View
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 7.3. Pinpointing the Location of a Device
      1. Problem
      2. Solution
      3. Discussion
    5. 7.4. Displaying Pins on a Map View
      1. Problem
      2. Solution
      3. Discussion
    6. 7.5. Displaying Pins with Different Colors on a Map View
      1. Problem
      2. Solution
      3. Discussion
    7. 7.6. Displaying Custom Pins on a Map View
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 7.7. Converting Meaningful Addresses to Longitude and Latitude
      1. Problem
      2. Solution
      3. Discussion
    9. 7.8. Converting Longitude and Latitude to a Meaningful Address
      1. Problem
      2. Solution
      3. Discussion
  10. 8. Implementing Gesture Recognizers
    1. 8.0. Introduction
    2. 8.1. Detecting Swipe Gestures
      1. Problem
      2. Solution
      3. Discussion
    3. 8.2. Detecting Rotation Gestures
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 8.3. Detecting Panning and Dragging Gestures
      1. Problem
      2. Solution
      3. Discussion
    5. 8.4. Detecting Long Press Gestures
      1. Problem
      2. Solution
      3. Discussion
    6. 8.5. Detecting Tap Gestures
      1. Problem
      2. Solution
      3. Discussion
    7. 8.6. Detecting Pinch Gestures
      1. Problem
      2. Solution
      3. Discussion
  11. 9. Networking, JSON, XML, and Twitter
    1. 9.0. Introduction
    2. 9.1. Downloading Asynchronously with NSURLConnection
      1. Problem
      2. Solution
      3. Discussion
    3. 9.2. Handling Timeouts in Asynchronous Connections
      1. Problem
      2. Solution
      3. Discussion
    4. 9.3. Downloading Synchronously with NSURLConnection
      1. Problem
      2. Solution
      3. Discussion
    5. 9.4. Modifying a URL Request with NSMutableURLRequest
      1. Problem
      2. Solution
      3. Discussion
    6. 9.5. Sending HTTP GET Requests with NSURLConnection
      1. Problem
      2. Solution
      3. Discussion
    7. 9.6. Sending HTTP POST Requests with NSURLConnection
      1. Problem
      2. Solution
      3. Discussion
    8. 9.7. Sending HTTP DELETE Requests with NSURLConnection
      1. Problem
      2. Solution
      3. Discussion
    9. 9.8. Sending HTTP PUT Requests with NSURLConnection
      1. Problem
      2. Solution
      3. Discussion
    10. 9.9. Serializing Arrays and Dictionaries into JSON
      1. Problem
      2. Solution
      3. Discussion
    11. 9.10. Deserializing JSON into Arrays and Dictionaries
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. 9.11. Integrating Twitter Functionality into Your Apps
      1. Problem
      2. Solution
      3. Discussion
    13. 9.12. Parsing XML with NSXMLParser
      1. Problem
      2. Solution
      3. Discussion
  12. 10. Audio and Video
    1. 10.0. Introduction
    2. 10.1. Playing Audio Files
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 10.2. Handling Interruptions while Playing Audio
      1. Problem
      2. Solution
      3. Discussion
    4. 10.3. Recording Audio
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 10.4. Handling Interruptions while Recording Audio
      1. Problem
      2. Solution
      3. Discussion
    6. 10.5. Playing Audio over Other Active Sounds
      1. Problem
      2. Solution
      3. Discussion
    7. 10.6. Playing Video Files
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 10.7. Capturing Thumbnails from a Video File
      1. Problem
      2. Solution
      3. Discussion
    9. 10.8. Accessing the Music Library
      1. Problem
      2. Solution
      3. Discussion
  13. 11. Address Book
    1. 11.0. Introduction
    2. 11.1. Requesting Access to the Address Book
      1. Problem
      2. Solution
      3. Discussion
    3. 11.2. Retrieving a Reference to an Address Book
      1. Problem
      2. Solution
      3. Discussion
    4. 11.3. Retrieving All the People in the Address Book
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 11.4. Retrieving Properties of Address Book Entries
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 11.5. Inserting a Person Entry into the Address Book
      1. Problem
      2. Solution
      3. Discussion
    7. 11.6. Inserting a Group Entry into the Address Book
      1. Problem
      2. Solution
      3. Discussion
    8. 11.7. Adding Persons to Groups
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 11.8. Searching the Address Book
      1. Problem
      2. Solution
      3. Discussion
    10. 11.9. Retrieving and Setting a Person’s Address Book Image
      1. Problem
      2. Solution
      3. Discussion
  14. 12. Files and Folder Management
    1. 12.0. Introduction
    2. 12.1. Finding the Paths of the Most Useful Folders on Disk
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 12.2. Writing to and Reading from Files
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 12.3. Creating Folders on Disk
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 12.4. Enumerating Files and Folders
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 12.5. Deleting Files and Folders
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    7. 12.6. Securing Files on Disk
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 12.7. Saving Objects to Files
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  15. 13. Camera and the Photo Library
    1. 13.0. Introduction
    2. 13.1. Detecting and Probing the Camera
      1. Problem
      2. Solution
      3. Discussion
    3. 13.2. Taking Photos with the Camera
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 13.3. Taking Videos with the Camera
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 13.4. Storing Photos in the Photo Library
      1. Problem
      2. Solution
      3. Discussion
    6. 13.5. Storing Videos in the Photo Library
      1. Problem
      2. Solution
      3. Discussion
    7. 13.6. Retrieving Photos and Videos from the Photo Library
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 13.7. Retrieving Assets from the Assets Library
      1. Problem
      2. Solution
      3. Discussion
    9. 13.8. Editing Videos on an iOS Device
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  16. 14. Multitasking
    1. 14.0. Introduction
    2. 14.1. Detecting the Availability of Multitasking
      1. Problem
      2. Solution
      3. Discussion
    3. 14.2. Completing a Long-Running Task in the Background
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 14.3. Receiving Local Notifications in the Background
      1. Problem
      2. Solution
      3. Discussion
    5. 14.4. Playing Audio in the Background
      1. Problem
      2. Solution
      3. Discussion
    6. 14.5. Handling Location Changes in the Background
      1. Problem
      2. Solution
      3. Discussion
    7. 14.6. Saving and Loading the State of Multitasking iOS Apps
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 14.7. Handling Network Connections in the Background
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 14.8. Handling Notifications Delivered to a Waking App
      1. Problem
      2. Solution
      3. Discussion
    10. 14.9. Responding to Changes in App Settings
      1. Problem
      2. Solution
      3. Discussion
    11. 14.10. Opting Out of Multitasking
      1. Problem
      2. Solution
      3. Discussion
  17. 15. Core Data
    1. 15.0. Introduction
    2. 15.1. Creating a Core Data Model with Xcode
      1. Problem
      2. Solution
      3. Discussion
    3. 15.2. Generating Class Files for Core Data Entities
      1. Problem
      2. Solution
      3. Discussion
    4. 15.3. Creating and Saving Data Using Core Data
      1. Problem
      2. Solution
      3. Discussion
    5. 15.4. Reading Data from Core Data
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 15.5. Deleting Data from Core Data
      1. Problem
      2. Solution
      3. Discussion
    7. 15.6. Sorting Data in Core Data
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 15.7. Boosting Data Access in Table Views
      1. Problem
      2. Solution
      3. Discussion
    9. 15.8. Implementing Relationships in Core Data
      1. Problem
      2. Solution
      3. Discussion
  18. 16. Dates, Calendars, and Events
    1. 16.0. Introduction
    2. 16.1. Retrieving the List of Calendars
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 16.2. Adding Events to Calendars
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 16.3. Accessing the Contents of Calendars
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 16.4. Removing Events from Calendars
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 16.5. Adding Recurring Events to Calendars
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    7. 16.6. Retrieving the Attendees of an Event
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 16.7. Adding Alarms to Calendars
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 16.8. Handling Event Changed Notifications
      1. Problem
      2. Solution
      3. Discussion
    10. 16.9. Presenting Event View Controllers
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    11. 16.10. Presenting Event Edit View Controllers
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  19. 17. Graphics and Animations
    1. 17.0. Introduction
    2. 17.1. Enumerating and Loading Fonts
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 17.2. Drawing Text
      1. Problem
      2. Solution
      3. Discussion
    4. 17.3. Constructing, Setting, and Using Colors
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 17.4. Drawing Images
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 17.5. Constructing Resizable Images
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    7. 17.6. Drawing Lines
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 17.7. Constructing Paths
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 17.8. Drawing Rectangles
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    10. 17.9. Adding Shadows to Shapes
      1. Problem
      2. Solution
      3. Discussion
    11. 17.10. Drawing Gradients
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    12. 17.11. Displacing Shapes Drawn on Graphic Contexts
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    13. 17.12. Scaling Shapes Drawn on Graphic Contexts
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    14. 17.13. Rotating Shapes Drawn on Graphic Contexts
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    15. 17.14. Animating and Moving Views
      1. Problem
      2. Solution
      3. Discussion
    16. 17.15. Animating and Scaling Views
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    17. 17.16. Animating and Rotating Views
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  20. 18. Core Motion
    1. 18.0. Introduction
    2. 18.1. Detecting the Availability of an Accelerometer
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 18.2. Detecting the Availability of a Gyroscope
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 18.3. Retrieving Accelerometer Data
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 18.4. Detecting Shakes on an iOS Device
      1. Problem
      2. Solution
      3. Discussion
    6. 18.5. Retrieving Gyroscope Data
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  21. 19. iCloud
    1. 19.0. Introduction
    2. 19.1. Setting Up Your App for iCloud
      1. Problem
      2. Solution
      3. Discussion
    3. 19.2. Storing and Synchronizing Dictionaries in iCloud
      1. Problem
      2. Solution
      3. Discussion
    4. 19.3. Creating and Managing Folders for Apps in iCloud
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 19.4. Searching for Files and Folders in iCloud
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 19.5. Storing User Documents in iCloud
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    7. 19.6. Managing the State of Documents in iCloud
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 19.7. Handling Conflicts in iCloud Documents
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  22. 20. Pass Kit
    1. 20.0. Introduction
    2. 20.1. Creating Pass Kit Certificates
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    3. 20.2. Creating Pass Files
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    4. 20.3. Providing Icons and Images for Passes
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    5. 20.4. Preparing Your Passes for Digital Signature
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    6. 20.5. Signing Passes Digitally
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    7. 20.6. Distributing Passes Using Email
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    8. 20.7. Distributing Passes Using Web Services
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    9. 20.8. Enabling Your iOS Apps to Access Passes on iOS Devices
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
    10. 20.9. Interacting with Passbook Programmatically
      1. Problem
      2. Solution
      3. Discussion
      4. See Also
  23. Index
  24. About the Author
  25. Colophon
  26. Copyright
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1.13. Defining Functionality for Classes

Problem

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

Solution

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

Discussion

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:

sendEmailTo("somebody@somewhere.com",
            "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("somebody@somewhere.com",
                                "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:@"someone@somewhere.com"
      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;

}

Warning

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 whom you work with on the same team, regardless of how well you might have documented your code.

We can call this method like so:

[self sendEmailTo:@"someone@somewhere.com"
                 :@"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;

@end

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;
}

@end

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

- (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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