This document summarizes new features in iOS development, including new Objective-C language features like NSNumber literals and boxed expressions, the use of storyboards to define view controller transitions and relationships, customizing UI elements globally with UIAppearance, and useful techniques like implementing singletons and using Grand Central Dispatch. It provides examples and demonstrations of these topics.

1. iOS Development:
What’s New
April 24, 2013

2. Topics for Today
• New Objective-C language features
• Storyboard
• UI Customization with UIAppearance
• Some useful stuff I learned this term

3. Objective-C: New Features
• NSNumber literals
• Boxed expressions
• NSArray & NSDictionary literals

4. NSNumber Literals
• NSNumber *anInt = [NSNumber numberWithInt: 10];
• NSNumber *aBool =[NSNumber numberWithBool: YES];
• NSNumber *aChar = *NSNumber numberWithChar: ‘z’+;
• Too much typing
• We have all used NSString literals such as @”this”
• NSNumber *aNum = @10;
• NSNumber *aBool = @YES;
• NSNumber *aChar = @’z’;

5. Boxed Expressions
• @( <an expression> )
• Eg. NSNumber *aDouble = @(2 * pi * r);
• Also works with cstrings, enums

6. Arrays and Dictionaries
• To create a NSArray or NSDictionary, we need to use factory
methods such as:
• [NSArray arrayWithObjects: obj1, @"abc", obj3, nil];
• [NSDictionary dictionaryWithObjectsAndKeys: obj1, obj2, key1,
key2, nil];
• To access an object:
• [array objectAtIndex: 1];
• *dictionary objectForKey: @”key”+;
• To modify/update/change an object:
• [array replaceObjectAtIndex: 1 withObject: @"new object"];
• [dictionary setObject: @"new Object" forKey: @"key3"];

7. Container Literals
• NSArray
• @*@”one”, @”two”, @”three”+;
• NSDictionary
• Just like JSON
• @, @”key1” : @”value1”, @”key2” : @”value2”-
• No more confusing factory methods

8. Demo

9. Storyboard

11. What’s Storyboard?
• A .storyboard is basically A huge XML file which contains
XCode Interface Builder information
• Comprised of individual “scenes” (Views + Controllers)
• Transitions/Relationships between scenes are defined by
“segues”

12. Advantages of Using
Storyboards
• Clearly defined flow
• Less nib file cluttering
• Reduce cluttering even more when you are making an
universal app
• Using segues saves you from writing millions of IBActions with
repetitive push and pop view controller codes.
• Too easy to use
• Build a working UI prototype extremely fast with almost zero
coding
• Storyboard knows about view-controllers, so you can create
more powerful views (eg. Static table view cells, prototype
cells)

13. Disadvantages of Using
Storyboards
• Impossible to merge storyboard changes
• Solution 1: Don’t work on it at the same time
• Solution 2: Based on program flow, use multiple storyboards
• Not backwards compatible with iOS 4- (also iOS 5 if you are
using features such as embedded segue for container view)

14. How to Integrate Storyboard in
Your App
• Each project can have a main storyboard set in project settings
• View controllers can also be loaded from storyboard files
programmatically:
• In this way, we can use multiple storyboards with NIBs.

15. Segues
• A segue defines a visual transition OR relationship between
two view controllers
• Examples of transition segues:
• Push segue (push view controller onto a navigation controller)
• Modal segue (presenting a view controller modally)
• Popover segue (Presenting a UIPopoverController, iPad only)
• Custom segue (subclass UIStoryboardSegue and override the
-perform method to do whatever you want. Can be reused in
Storyboard)
• Examples of relationship segues:
• A empty navigation controller has a relationship segue to its root
view controller
• A container view has a embed segue to its child view controller

16. Performing Segue
• Define a segue by ctrl-drag from a control (such as UIButton)
to another view controller
• Will be triggered when the specified action is performed on that
control
• Define a segue by ctrl-drag from a view controller to another
view controller
• Segue needs to be triggered manually by calling
–performSegueWithIdentifier:sender:

18. Pass Data Between Controllers
• Implement prepareForSegue:(UIStoryboardSegue *)sender:(id) in
the view controller that will initiate the segue
• This method is called before a segue is about to be performed
• The UIStoryboardSegue parameter contains the following
properties: identifier, sourceViewController, and
destinationViewController
• Now you can set properties and send messages to these
controllers!

19. Unwind Segues
• Unwind segue is a segue that jump back to previous scenes
• To unwind from controller B back to controller A:
1. In controller A, create a method that takes a
UIStoryboardSegue as parameter with return type IBAction
2. In storyboard, select controller B, ctrl-drag from a control to the
“Exit” icon at the bottom of the controller
3. Select the method that you defined in B. The unwind segue has
been created.
4. On the left panel of the interface builder, select the unwind
segue and give it an identifier.
5. prepareForSegue:sender: will be called in B, and then the
IBAction method in A will be called

20. Storyboard: Conclusion
• You can avoid using delegation pattern in some cases if you
use segues
• With iOS 7 introduction due in June, we should start building
new apps with storyboards (and autolayout)

21. UI Customization with
UIAppearance Protocol
• Customize UIKit objects (eg. UIView, UIButton,…) globally
• Customize specific elements depending on view hierarchy

22. Demo

23. Useful iOS Stuff

24. Singleton Best Practices
• Restricting instantiation of a class to one object only
• Example: ServiceManager
• One object is then shared by many
• Issue: Instantiation in a multi-threaded environment

25. Basic Singleton
• Not thread-safe

26. Mutex Lock
• Takes lock every time when you only needs to lock it once.
Expansive.

27. -Initialize
• If you send any message to the class, singleton object will be
created.

28. Double-checked Locking
• Check if singleton is instantiated before and after taking lock
• Memory barriers ensures all load and store CPU operations
completes before proceeding
• Doesn’t take lock every time, but still have to pay for
OSMemoryBerrier()

29. Grand Central Dispatch
• As fast as non-thread safe version
• Similar to double checked locking, but avoid
OSMemoryBarrier() penalty
• Guaranteed run only once

30. Custom Container View
Controllers
• Embed multiple view controllers in one view controller
• Adding, removing, and transition between child view
controllers
• Its like implementing your own UINavigationController or
UITabBarController

31. Adding / Removing
Child View Controllers

32. Transition Between Child View
Controllers

33. Grand Central Dispatch is
really good, but I don’t have
time to finish the slide!
• Efficient, fast C API
• dispatch_sync, dispatch_async, dispatch_after to queue operations
• dispatch_semaphore, dispatch_group, dispatch_barrier for
synchronization
• You can create your own serial OR concurrent queues with
dispatch_queue_create
• dispatch_apply for concurrent enumeration on an array
• Create “dispatch sources” such as dispatch timers that attach to a
queue and fire periodic events
• Use dispatch_io to do sync/async operations on file descriptors

34. Thank you!
• Any questions?