Objective-C Part 2 (ECS189H) Ken Joy Serban Porumbescu

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1 Objective-C Part 2 (ECS189H) Ken Joy joy@cs.ucdavis.edu Serban Porumbescu porumbes@cs.ucdavis.edu

2 Today Objective-C Memory Management Properties Categories and Protocols Delegates

3 Objective-C Memory Management

4 Memory Management Reference counting Based on an agreement Responsible for cleaning up

5 Reference Counting Object tracks number of other objects referring to it When count 0, memory is freed

6 The agreement You re responsible for n.a.r.c Own objects sent messages containing new alloc retain copy

7 The agreement You must send objects you own release message when done

8 reference count = 1 Dog *mydog = [Dog alloc];

9 reference count = 2 Dog *mydog = [Dog alloc]; Dog *d2 = [mydog retain];

10 reference count = 3 Dog *mydog = [Dog alloc]; Dog *d2 = [mydog retain]; Dog *d3 = [mydog retain];

11 reference count = 4 Dog *mydog = [Dog alloc]; Dog *d2 = [mydog retain]; Dog *d3 = [mydog retain]; Dog *d4 = [d3 retain];

12 reference count = 4 mydog d2 d3 d4

13 reference count = 4 [mydog release]; d2 d3 d4

14 reference count = 3 d2 d3 d4

15 reference count = 3 d2 [d3 release]; d4

16 reference count = 2 d2 d4

17 reference count = 2 d2 [d4 release];

18 reference count = 1 d2

19 reference count = 1 [d2 release];

20 reference count = 0

21 reference count = 0

22 Memory Management: autorelease You own objects you create new alloc copy Or take ownership using retain

23 Thingamajig *mythingamajig = [[Thingamajig alloc] init]; //... NSArray *sprockets = [mythingamajig sprockets]; //... [mythingamajig release];

24 What Happens? + (Thingamajig *)thingamajig { id newthingamajig = [[Thingamajig alloc] init]; return newthingamajig; }

25 What Happens? + (Thingamajig *)thingamajig { id newthingamajig = [[Thingamajig alloc] init]; return newthingamajig; } Based on our rules, this is WRONG!

26 How About This? + (Thingamajig *)thingamajig { id newthingamajig = [[Thingamajig alloc] init]; [newthingamajig release]; return newthingamajig; }

27 How About This? + (Thingamajig *)thingamajig { id newthingamajig = [[Thingamajig alloc] init]; [newthingamajig release]; return newthingamajig; // newthingamajig is invalid here } WRONG!

28 Solution: autorelease + (Thingamajig *)thingamajig { id newthingamajig = [[Thingamajig alloc] init]; return [newthingamajig autorelease]; }

29 Objective-C Properties Generate setters and getters Behavior based on attributes set

30 Getter / Setter code examples WARNING: memory issues

31 @interface Dog : NSObject { NSString *name; int age; } - (NSString*)name; - (void)setname:(nsstring*)newname; - (int)age; -

32 @implementation Dog - (NSString*)name{ return name; } - (void)setname:(nsstring *)newname{ name = newname; } - (int)age{ return age; } - (void)setage:(int)newage{ age = newage;

33 Dog *dog = [[Dog alloc] init]; [dog setage:5]; [dog setname:@"woofy"]; NSLog(@"name = %@", [dog name]); NSLog(@"age = %d", [dog age]);

34 Using Dog : NSObject { NSString *name; int age; (copy) NSString int

35 @implementation age; - (void)dealloc{ [name release]; [super dealloc];

36 Dot Notation dog.age = 20; dog.name NSLog(@"name = %@", dog.name); NSLog(@"age = %d", dog.age);

37 Property (attribute1, attribute2,...) PropertyType propertyname;

38 Property Attribute Types Writability readwrite (default) readonly (no setter) Setter Semantics assign (bitwise copy) retain (increment reference count) copy (deep copy)

39 Property (readonly) PropertyType (copy) PropertyType propertyname;

40 Categories and Protocols

41 Categories Add new methods to existing class Don t need original class source code Naming convention

42 NSString+MyName.h #import NSString (MyName) // add new methods

43 NSString+MyName.m #import NSString (MyName) // define methods

44 Category Uses Extend classes implemented by others (e.g., Apple) Alternative to inheritance Distribute implementation across multiple files Informal Protocols (list of methods to implement)

45 Protocols Declare methods others can or should implement Often used to define interface for delegates

46 @protocol LexmeeBoardManagerDelegate<NSObject> - (void)correctword; - (void)duplicateword; - (void)incorrectword; -

47 @interface MyClass : NSObject <UIApplicationDelegate>

48 Delegates An object given a chance to do something for another object Minimize coupling between objects

49 Delegation Boss Object Assistant Object id delegate

50 Delegation Boss Object Doing A Assistant Object dostuff [delegate dostuff] Doing B domore [delegate domore]

51 Some Examples

Design Phase. Create a class Person. Determine the superclass. NSObject (in this case)

Design Phase. Create a class Person. Determine the superclass. NSObject (in this case) Design Phase Create a class Person Determine the superclass NSObject (in this case) 8 Design Phase Create a class Person Determine the superclass NSObject (in this case) What properties should it have?