Mobile Application Programming. Objective-C Classes

Transcription

1 Mobile Application Programming Objective-C Classes

2 Custom Car : NSObject #import Car.h + (int) viper; - (id) Car Point position; float velocity; int model; NSString* vin; - (Point) position; - (void) + (int) viper return 1 ; - (id) initwithmodel:(int)m position = PointMake(0.0f, 0.0f); velocity = 0.0f; model = m; vin HDGV ; return self; - (Point) position return position; - (void) setposition:(point)p position = p;

3 Class Constructors Destructors Convenience Constructors (0.2,0.5,-0.3) Accessors Description Mutators

4 Class Constructors Destructors Convenience Constructors (0.2,0.5,-0.3) Accessors Description Mutators

5 Constructors Constructors in ObjectiveC are prefixed with init - (id) initwithmodel:(int)m position = PointMake(0.0f, 0.0f); velocity = 0.0f; model = m; vin HDGV ; return self; All constructors should invoke their super-class init All constructors must return self - (id) initwithmodel:(int)m self = [super init]; if (self == nil) return nil; position = PointMake(0.0f, 0.0f); velocity = 0.0f; model = m; vin HDGV ; If the construction fails, must return nil return self;

6 Class Constructors Destructors Convenience Constructors (0.2,0.5,-0.3) Accessors Description Mutators

7 Destructors Destructors in Objective-C are implemented with the dealloc method Destructors should clean up services that the class relies on (file handles, network connections, etc) Memory management is handled by ARC - (void) dealloc [file close];

8 Automatic Reference Counting (ARC) Objective-C used to have manual memory management ARC replaces that model ARC is NOT Garbage Collection Inserts retain / release calls automatically Use strong and weak property qualifiers as well as strong and weak variable qualifiers to set lifetime

9 Class Constructors Destructors Convenience Constructors (0.2,0.5,-0.3) Accessors Description Mutators

10 Accessors and Properties Get methods aren t prefixed with get. Just use the name of the object property (eg. position, not getposition) Set methods are prefixed with set. (eg. setposition) - (Point) position return position; - (void) setposition:(point)p position = p; - (NSString*) name return name; - (void) setname:(nsstring*)n name = n;

11 Accessors and Properties Manually creating getters and setters is time consuming and takes a lot of code. If they are standard getters and setters, properties were created to automatically generate them. //.h file - (NSString*) name; - (void) setname:(nsstring*)n; //.m file - (NSString*) name return name; - (void) setname:(nsstring*)n name = n; //.h (strong) NSString* name; //.m name = someothervar; // Optional

12 Accessors and NSString* objectvariable; objectvariable; //.m (Optional) (strong) NSString* objectvariable; objectvariable; //.m float primitivevariable; primitivevariable; //.m (Optional) (unsafe_unretained) float primitivevariable; primitivevariable; //.m (Optional)

13 ARC and Variables Read Only (Generates just (readonly) float primitivevariable; primitivevariable; //.m (Optional) Strong / Weak Lifetime (strong) NSString* objectvariable; objectvariable; //.m (weak) NSString* objectvariable; objectvariable; //.m (Optional) Copy vs Shared (copy) NSString* name; name; //.m (Optional) Atomic vs Non-Atomic (nonatomic, weak) NSString* name; name; //.m (Optional)

14 ARC and Variables Primitive Types (Require no lifetime statements) float speed = 5.0f; // Variable exists until it goes out of scope Object Type Strong / Weak Lifetime Qualifiers NSString* strong name; // This pointer keeps referenced instance alive NSString* weak name; // This pointer does not, and goes nil automatically Example NSString* weak message = nil; // Pointer empty, will attach to message later if (true /* sky is blue */) NSString* strong actualmessage = [NSString stringwithformat:@ Car on level %i., 2]; message = actualmessage; NSLog(@ Message: %@, message); // Will print out Message: Car on level 2. NSLog(@ Message: %@, message); // Will print out Message: (null), as no strong pointers point to the // string instance anymore, so it is deallocated and the variable // message is set to nil. actualmessage went out of scope

15 Dot Notation Accessors and Mutators can use an alternate dot notation that functions exactly the same as standard notation. Dot accessor only possible when no arguments are required to call the accessor Dot mutator only possible when the value being set is the only argument The type of the receiver must be known (not an id)

16 Class Constructors Destructors Convenience Constructors (0.2,0.5,-0.3) Accessors Description Mutators

17 Description - (NSString*) description return [NSString stringwithformat:@ (%f,%f,%f), _x, _y, _z]; //... VCVector* v = [VCVector vectorwithx:0.1f y:0.5f z:-0.4f]; NSLog(@ v = %@, v);

18 Class Constructors Destructors Convenience Constructors (0.2,0.5,-0.3) Accessors Description Mutators

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