CS193p Spring 2010 Thursday, April 29, 2010

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Leon Perry
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1 CS193p Spring 2010

2 Announcements You should have received an by now If you received approving enrollment, but are not in Axess, do it! If you have any questions, please ask via or after class. If you have not installed SDK and gotten it working, talk to us after class. Homework Strongly recommend trying a submission today even if you re not yet done Multiple attempted submissions is no problem Assignments are to be done individually (except approved pairs for final project) Honor code applies Any questions about the homework?

3 Communication Questions are best sent to Sending directly to instructor or TA s risks slow response. Web Site Very Important! All lectures, assignments, code, etc. will be there. This site will be your best friend when it comes to getting info.

4 Today s Topics Objective-C Instance Variables Methods (Class and Instance) Properties Dynamic vs. Static Binding Introspection Protocols and Delegates Foundation Framework NSObject, NSString, NSMutableString NSNumber, NSValue, NSData, NSDate NSArray, NSDictionary, NSSet NSUserDefaults, etc. Memory Management Allocating and initializing objects Reference Counting

5 Instance Variables By default, they are protected Only methods in the class itself and subclasses can see them Can be marked private Can be marked public Don t do it! Use properties instead. Ship : Vehicle { Size int NSString *dontdothisstring; }

6 Methods If public, declare them in.h file. Public or private, implement them in.m file. - (NSArray *)findshipsatpoint:(cgpoint)bombdrop withdamage:(bool)damaged ; 1. Specify class method with + or instance method with - (more on this later) 2. Then return type in parentheses (can be void if returns nothing) 3. Then first part of name of method, always ending in : unless zero args 4. Then type of first argument in parentheses 5. Then name of first argument 6. If more arguments, next comes a required space, then repeat Then semicolon if declaring, or code inside { } if implementing Spaces allowed between any of the above steps, but no spaces in step 3 or 5

7 Instance Methods Declarations start with a - (a dash) Normal methods you are used to Instance variables usable inside implementation Receiver of message can be self or super too self calls method in calling object (recursion okay) super calls method on self, but uses superclass s implementation If a superclass calls a method on self, it will use your implementation Calling syntax: BOOL destroyed = [ship dropbomb:bombtype at:droppoint];

8 Class Methods Declarations start with a + (a plus sign) Usually used to ask a class to create an instance Sometimes hands out shared instances Or performs some sort of utility function Not sent to an instance, so no instance variables can be used in the implementation of a class method (and be careful about self in a class method... it means the class object) Calling syntax: Ship *ship = [Ship shipwithturrentcount:3]; Ship *mother = [Ship mothership]; int size = [Ship turretcountforshipsize:shipsize];

9 Properties Replaces - (double)operand; Note lowercase o then uppercase O Use this convention for properties. - (void)setoperand:(double)anoperand; double operand; Implementation replaced operand; // if there s an instance variable operand = op; // if corresponding ivar is op Callers use dot notation to set and get double x = brain.operand; brain.operand = newoperand;

10 Properties Properties can be read only (no (readonly) double operand; You can and still implement the setter or the getter yourself (one of them) - (void)setmaximumspeed:(int)speed { if (speed > 65) { speed = 65; } maximumspeed = speed; maximumspeed would still create the getter even with above implementation

11 Properties Using your own (self s) pro perties What does this code do? - (int)maximumspeed { if (self.maximumspeed > 65) { return 65; } else { return maximumspeed; } } Infinite loop!

12 nil nil is the value that a variable which is a pointer to an object (id or Foo *) has when it is not currently pointing to anything. Like zero for a primitive type (int, double, etc.) (actually, it is not just like zero, it is zero) NSObject sets all its instance variables to zero (thus nil for objects) Can be implicitly tested in an if statement: if (obj) { } means if the obj pointer is not nil Sending messages to nil is (mostly) A-OK! If the method returns a value, it will return 0 Be careful if return value is a C struct though! Results undefined. e.g. CGPoint p = [obj getlocation]; // if obj is nil, p undefined

13 BOOL BOOL is Objective-C s boolean value Can also be tested implicitly YES means true, NO means false NO is zero, YES is anything else if (flag) { } means if flag is YES if (!flag) { } means if flag is NO if (flag == YES) { } means if flag is YES if (flag!= NO) { } means if flag is not NO

14 Dynamic vs. Static NSString * versus id id * (almost never used, pointer to a pointer) Compiler can check NSString * Compiler will accept any message sent to id that it knows about (i.e. it has to know some object somewhere that knows that message) Force a pointer by casting: (NSString *)foo Regardless of what compiler says, your program will crash if you send a message to an object that does not implement that method

15 @interface Ship : Vehicle - Ship *s = [[Ship alloc] init]; [s shoot]; Examples Vehicle *v = s; [v shoot]; // compiler will warn, no crash at runtime in this case Ship *castedvehicle = (Ship *)somevehicle; // dange ro u s!!! [castedvehicle shoot]; // compiler won t warn, might crash id obj =...; [obj shoot]; [obj lskdfjslkfjslfkj]; [(id)somevehicle shoot]; // compiler won t warn, might crash // compiler will warn, runtime crash // n o war ning, mig ht crash Vehicle *tank = [[Tank alloc] init]; [(Ship *)tank shoot]; // n o war ning, crashe s at r untim e

16 Introspection iskindofclass: Can be sent to any object and takes inheritance into account Takes a Class object as its argument (where do I get one?) [NSString class] or [CalculatorBrain class] or [obj class] Syntax: if ([obj iskindofclass:[nsstring class]]) { ismemberofclass: Can be sent to any object but does NOT take inheritance into account Syntax: if ([obj ismemberofclass:[nsstring class]]) { This would be false if obj were NSMutableString classname Returns the name of the class as an NSString Syntax: NSString *name = [obj classname];

17 Introspection respondstoselector: Can be sent to any NSObject to find out if it implements a certain method Needs a special method token as its argument (a selector Syntax: if ([obj respondstoselector:@selector(shoot)]) { SEL The type of a selector is SEL, e.g., - (void)performselector:(sel)action Important use: set up target/action outside of Interface Builder Syntax: [btn addtarget:self action:@selector(shoot)...] performselector: Send a message to an NSObject using a selector Syntax: [obj performselector:@selector(shoot)] Syntax: [obj performselector:@selector(foo:) withobject:x]

18 Introspection Example id anobject =...; SEL aselector if ([anobject respondstoselector:aselector]) { [anobject performselector:aselector withobject:self]; }

19 Foundation Framework NSObject Base class for pretty much every object in iphone SDK Frameworks Implements memory management primitives (more on this in a moment) and introspection - (NSString *)description is a useful method to override, it s %@ in NSLog NSString International (any language) strings Used throughout all of iphone SDK instead of C s char * Cannot be modified! Usually returns you a new NSString when you ask it to do something Tons of utility functions (case, URLs, conversion to/from lots of other types, substrings, file system paths, and much much more!) Compiler will create a constant one for you foo NSMutableString Mutable version of NSString Can do some of the things NSString can do without making a new one

20 Foundation Framework NSNumber Object wrapper around primitive types: int, float, double, BOOL, etc. Use it when you want to store those in an NSArray or other object NSValue Generic object wrapper for any non-object data type. Useful for wrapping graphics things like a CGPoint or CGRect NSData Bag of bits Used to save/restore/transmit data throughout the SDK NSDate Can be used to find out the time now or store a past/future time See also NSCalendar, NSDateFormatter, NSDateComponents

Stanford CS193p. Developing Applications for iphone 4, ipod Touch, & ipad Spring Stanford CS193p Spring 2011

Stanford CS193p. Developing Applications for iphone 4, ipod Touch, & ipad Spring Stanford CS193p Spring 2011 Developing Applications for iphone 4, ipod Touch, & ipad Today Dynamic Binding Introspection Foundation Framework Enumeration More Objective-C Allocating and Initializing objects Memory Management Demo