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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
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1.11. Implementing While Loops

Problem

You want to let a piece of code run over and over again until a certain condition is met.

Solution

Use while loops and specify your exit condition. Here is the format for the while loop:

while (<replaceable>condition</replaceable>){
  CODE
}

Note

As long as the condition is a value other than zero/nil/NULL, the while loop will run.

Discussion

The while loop is the arrogant brother of the for loop (see Recipe 1.10) because while loops only take a condition that should be met for the loop to run. If the condition is positive, the loop will always run until the condition becomes negative. For instance, a while loop could be implemented to make an icon in the Dock in Mac OS X jump up and down until the user taps on that icon (this is actually a very bad user experience; icons in the Dock shouldn’t jump up and down continuously, but for a short interval, or even a fixed number of times, usually 3). The exit condition for the while loop is the user’s tapping on that icon. As long as the user hasn’t tapped on the icon, the icon will jump up and down.

A while loop is awkward to use with a counter because of its syntax. If you require a counter to control your loop, it is better to use a for loop. If you do require a while loop but still want to have access to a counter, you will need to manage the counter manually, like so:

NSUInteger counter = 0;
while (counter < 10){
  NSLog(@"Counter = %lu", (unsigned long)counter);
  counter++;
}

Just as you can have positive conditions for your while loops, you can have negative conditions as well:

BOOL shouldExitLoop = NO;
NSUInteger counter = 0;

while (shouldExitLoop == NO){
       counter++;
  if (counter >= 10){
    shouldExitLoop = YES;
  }
}

NSLog(@"Counter = %lu", (unsigned long)counter);

The output of this program is:

Counter = 10

So what we are doing is simply running a loop for as long as our counter is less than 10. If the value of the counter (adjusted inside the loop itself) goes over or becomes equal to 10, then we exit our loop. Just like a for loop, you can create an infinite loop using a while loop, although this is a terrible programming practice and you should avoid it by all means:

while (YES){
  /* Infinite loop */
}

You must make sure that you have an exit strategy in your while and for loops. For this, you need to keep an eye on the condition for your loops and make sure that the condition will be met at some point, without making your loops hogging all the memory and/or system resources while they run, while using autorelease objects. As you know, an autorelease object only gets released when the autorelease pool owning that object gets drained or released. If you do not have an autorelease pool inside your loop continuously releasing autorelease objects, your loop might end up consuming too much memory and your app might get terminated by iOS.

Here is another usage of a while loop:

char *myString = "Some Random String";
NSUInteger counter = 0;
char character;
while ((character = myString[counter++]) != 'R' &&
       counter < strlen(myString)){
  /* Empty */
}
NSLog(@"Found the letter R at character #%lu", (unsigned long)counter+1);

Here we are searching inside a string for the first occurrence of the letter R. As soon as we find it, we exit our while loop. We have included another condition: if we reach the end of the string (strlen(myString)), we end the loop, so we don’t wander off into undefined memory and cause a crash or a security flaw. (This is called a buffer overflow.)

This algorithm has a bug, however: it returns a wrong results when the letter R isn’t in the string at all. Because the while loop finishes when we get to the end of the string, we always print a message to the console saying that the letter R was found at some index. I will leave it up to you to fix this algorithm. As a hint, you might want to use a Boolean value when you do find the letter R and then later use that flag to determine whether the letter was found. To use that boolean technique, you might need to change the way the while loop is set up, but I think you get the idea.

A while loop is useful for traversing an array. For instance, a C String is an array of characters ending with a zero byte. If you are searching for a specific character in this array, you can simply write a while loop that starts from the first character and runs until it finds the zero terminator that ends the string. Here is an example:

char *cString = "My String";
char *stringPointer = cString;
while (*stringPointer != 0x00){
  NSLog(@"%c", *stringPointer);
  stringPointer++;
}

This example will print all the characters inside the string until it gets to the zero terminator of the string. Using a while loop, you can even create a function similar to the strlen() function that is able to find the length of a C String, like so:

NSUInteger lengthOfCString(const char *paramString){

  NSUInteger result = 0;

  if (paramString == NULL){
    return 0;
  }

  char *stringPointer = (char *)paramString;

  while (*stringPointer != 0x00){
    result++;
    stringPointer++;
  }

  return result;

}

Note

It’s better to use the built-in strlen for two reasons: it has been optimized to make the best use of the underlying hardware, and it’s less likely to contain a bug.

See Also

Recipe 1.10

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