CS 185C/286 - Lecture 11

Cay S. Horstmann

Lecture 11 Quiz 1

What does this code do?

NSUInteger* day = [cal ordinalityOfUnit:NSMonthCalendarUnit
   inUnit:NSYearCalendarUnit
   forDate:now];

1. It gets the day of now
2. It gets the month of now
3. It's a syntax error because the colons don't line up
4. It's a syntax error because day shouldn't be a pointer

Lecture 11 Quiz 2

What is wrong with this code fragment?

NSString* greeting = @"Hello";
      if (!(greeting == @"Farewell"))
        NSLog(@"We will meet again");

1. greeting shouldn't be a pointer
2. There shouldn't be @ before the strings
3. You can't compare NSString references with ==
4. You need braces in the body of the if statement

Today's Lecture/Lab

• More about iOS and Objective-C
• Thanks to Dr. Pollett for letting me adapt his slides

Garbage Collection

• Invented around 1959 for Lisp
• As old as your professor!
• Became mainstream with Java
• Unfortunately, Objective-C predates that
• C: Manual memory management with malloc, free
• Apple's Objective-C uses reference counting
• Call [obj retain] to increment its count, [obj release] to decrement
• Automatic reference counting inserts these calls automatically
• Implement dealloc method. If reference count reaches 0, that's called.

  -(void)dealloc
  {
   /* call release on instance variable; then... */
   [super dealloc];
  }
        

• Only works in the absence of cycles
• An effort at proper garbage collection failed with Apple's Objective-C 2.0

Inheritance

• @interface Subclass : Superclass
• Cosmic superclass Object
• We usually extend at least NSObject
• super is like in Java:

  -(id) init { 
  self = [super init];
  // ...
  return self;
  }
    

More GUI Minutiae

• You can have more than one form of an action method

  -(IBAction) actionMethod;
  -(IBAction) actionMethod:(id)sender;
  -(IBAction) actionMethod:(id)sender withEvent:(UIEvent *)event;
          

• All UI components are subclasses of UIControl
• Each control can trigger multiple actions depending on how they are touched. For example, a finger swipe might do something different than a tap.

More Objective-C Trivia

•         @property (retain, nonatomic) UILabel *statusText;
          

• retain means that retain is called whenever this property is copied.
• nonatomic means that no lock code is inserted to make access threadsafe
• Objective-C was defined before C had a boolean type. To do booleans in Objective-C you declare a variable to be of type BOOL. This has two values: YES or NO.

Reading Before Next Class

• Dr. Pollett recommends the book by Hillegass for learning Objective-C.
• Read chapters 17 - 20

Lab

• Bring your laptop to the lab
• You will work with a buddy
• For this lab, match yourself up with a buddy who has a Mac
• I want you to submit your lab code to git. But don't use the git support in the IDE. Why not?
• Instead, either tell XCode to put your (unmanaged) project into the workspace/lab11 directory, or if you feel adventurous, look at these efforts to make git play nice with symlinks.
• Today, we simply follow in Dr. Pollett's footsteps. Start here.. In your report, tell me how far you got.