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
O'Reilly logo

1.9. Comparing Values in Objective-C with an if Statement

Problem

You want to compare two values in Objective-C.

Solution

Use if statements. Please refer to the Discussion section of this recipe for more information about different scenarios under which you might want to use if statements.

Discussion

We use if statements in our everyday conversations. For instance, you might say “If I get a hold of him, I’ll tell him...” or “I would put the computer to sleep if it didn’t take so long to come back up.” All these statements have a condition. If statements in Objective-C also have a condition. You can even make them more sophisticated, having your app do something if a condition is met and something else if the condition is not met. The basic form of an if statement is:

if (condition){
  /* Your code to get executed if the condition is met */
}

Note

As long as the condition is a value other than zero/nil/NULL, the code inside the if statement will run.

An if statement that has an “otherwise” clause in it is known as an if-else statement, and its format is:

if (condition){
  /* Your code to get executed if the condition is met */
} else {
  /* Code to get executed if condition is not met */
}

The else clause of the if-else statement can also contain its own if statement! That might sound strange, but consider this scenario. In real life, you can say something similar to this: “I will go get a cup of coffee. If the place is open, I will get a tall latte; if it’s closed and the other place is open, I will get a cappuccino; otherwise, I will just come back home and make tea for myself”. The part where we said “...if it’s closed and the other place is open...” is an else statement with an if statement embedded in it. Here is how you would implement that in Objective-C:

if (Coffee place A is open){
  Get a Tall Latte from coffee place A} else if (Coffee place B is open){
  Get a Cappuccino from coffee place B
} else {
  Come back home and make tea
}

The condition for an if statement, regardless of whether it is a standalone if statement (like the first condition in the last example) or embedded inside an else statement, must resolve to a boolean value. A boolean value is either YES or NO. For instance, the following code will always get executed, regardless of which condition/device you run it on:

if (YES){
  /* This code will get executed whenever the app gets to it */
} else {
  /* The app will NEVER get here */
}

The reason behind this is that the condition for the if statement in this example is always met as long as the YES is the condition. To make things more exciting, you can do comparisons in the condition supplied to an if statement, like so:

NSInteger integer1 = 123;
NSInteger integer2 = 456;

if (integer1 == integer2){
  NSLog(@"Integers are equal.");
} else {
  NSLog(@"Integers are not equal.");
}

Warning

Note that a double equal sign is used inside the conditional. A common error is to use a single equal sign, which is a totally different operator. The double equal sign does a comparison and returns a Boolean result, which is what you normally want in a conditional. A single equal sign changes the value of the left-hand variable and returns the value set, which the condition tries to interpret as a Boolean value. Although occasionally appropriate, it’s usually a serious error to use a single equal sign.

If you are comparing objects, it is best to use the isEqual: instance method of the NSObject class:

NSObject *object1 = [[NSObject alloc] init];
NSObject *object2 = object1;

if ([object1 isEqual:object2]){
  NSLog(@"Both objects are equal.");
} else {
  NSLog(@"Objects are not equal.");
}

Note

For now, you don’t have to worry about what objects are. This will be explained in detail in other recipes in this chapter.

Some objects such as strings, however, have their own comparison methods, changing the way we compare two strings. For instance, you can have two string objects that contain the same characters. If you compare them using their isEqual: instance method, you will get the result NO, because they are different objects. However, they might still contain the exact same characters. Because of this, different classes expose their own comparison methods in Objective-C. For more information about classes, please refer to Recipe 1.12. To learn more about objects, refer to Recipe 1.15.

An if statement and its else statement can be written with or without curly braces. Using the former syntax (with curly braces), you can execute multiple lines of code after the condition is satisfied. However, without curly braces, you can write only one line of code for each condition. Here is an example of the latter syntax without curly braces:

NSString *shortString = @"Hello!";

if ([shortString length] == 0)
  NSLog(@"This is an empty string");
else
  NSLog(@"This is not an empty string.");

Warning

Be extra careful with logging and if statements without curly braces. Often, when a product goes to production, a production manager might attempt to comment out all your NSLog methods simply by replacing all occurrences of NSLog with //NSLog. If you have if statements without curly braces, as in our last example, the production manager’s commented-out code will look like this:

NSString *shortString = @"Hello!";

if ([shortString length] == 0)
  //NSLog(@"This is an empty string");
else
  //NSLog(@"This is not an empty string.");

This will break the code and people in the company will not be happy. It doesn’t matter whether they are not happy at you or not happy at the production manager. That would be a team effort gone wrong, so you will all be to blame. To avoid this, make sure that you always write your if statements with curly braces.

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