objective-c
DESCRIPTION
MORE on classes in …. Objective-C. OOP terminology in Objective-C. Class: defines the grouping of data and code type of entity Object or Instance: a specific instantiation of a class with its own state (class variables values) Method: - PowerPoint PPT PresentationTRANSCRIPT
MORE on classes in …..
OOP terminology in Objective-CClass:
defines the grouping of data and code type of entity
Object or Instance: a specific instantiation of a class with its own state
(class variables values)
Method: a “function/operator” that an object knows how to
perform
Instance Variable: this is what we call class variable in other OOP
languages
Objective-C as an OOP langStrict superset of C Mix C with ObjC Or even C++ with ObjC (usually referred to as ObjC++)
A very simple language, but some new syntaxSingle inheritance, classes inherit from one
and only one superclassProtocols define behavior that cross classesDynamic runtimeLoosely typed, if you’d like
More on Objective-C Syntax:What’s most confusing about Objective-C?•Most class names start with NS: NSString, NSObject•Parameter lists are not comma delimited and method names are interrupted by parameter names and types.•There are too many brackets and colons. :[•Memory Management.•All these @ symbols confuse me.•Both C and Objective-C methods are allowed? Weird.
Objective-C Class MethodsInstances/Objects respond to instance methods- (id)init;- (float)height;- (void)walk;
Classes respond to class methods+ (id)alloc;+ (id)person;+ (Person *)sharedPerson; [ClassName
person]
[object walk]
Intro to Objective-C Syntax: Method SignaturesIn Java or C:void doNothing() { // nothing}int addThree(int x) { return x + 3; }int multiplyThreeParameters(int x, int y, int z) { return x * y * z;}
// note methods with multiple parameters are given in a parameter list // that is delimited by commas.
Keyreturn typemethod name
parameter typeparameter
name
Intro to Objective-C Syntax: Method SignaturesIn Objective-C- (void) doNothing { // nothing}- (int) addThree:(int) x { return x + 3; }- (int) multiplyThis:(int) x ByThis:(int) y AndThis:(int) z { return x * y * z;}
Keyreturn typemethod name
parameter typeparameter
name
NOTE: methods of Objective-C classes with multiple parameters have a to delimit the end of the parameter name and the continuation of the method name. Actually method name is multiplyThis:ByThis:AndThis
Stop---that was weird---method name is change of the 3
- (int) multiplyThis:(int) x ByThis:(int) y AndThis:(int) z { return x * y * z;}
Method name is
multiplyThis:ByThis:AndThis
Intro to Objective-C Syntax: Accessing methods of objects
In Java: object.method(param1, param2);
In C++: object->method(param1, param2);
In C: (no objects) method(param1, param2);
In Objective-C: [object method:param1 method:param2];
Only a space between no comma
Intro to Objective-C Syntax: Accessing methods of objectsIn Objective-C: [object method:param1 method:param2];
Example:If you have a string:NSString *msg = @"ALL YOUR BASES BELONG TO US";
And you want to split the sentence into an array of words:NSArray *words = [msg componentsSeparatedByString: @" "];
// The @ is required for all string literals, and encodes the string using UTF8
Intro to Objective-C Syntax: Instantiation / Memory AllocationIn Java:Object o = new Object();// Java takes care of garbage collection. In this statement, memory // is automatically allocated for the new object. Memory is also
// automatically released when the object is no longer in use.
In C:Object *o = (Object *) malloc(sizeof(Object));free (o);
In C++:Object *o = new Object; delete (o);
Intro to Objective-C Syntax: InstantiationIn Objective-C:Object *obj = [[Object alloc] init];
Ways of creating objectsAsking other objects to create objects for you
NSString’s - (NSString *)stringByAppendingString:(NSString *)otherString; NSString’s & NSArray’s - (id)mutableCopy; NSArray’s - (NSString *)componentsJoinedByString:(NSString *)separator;
Not all objects handed out by other objects are newly created
NSArray’s - (id)lastObject; NSArray’s - (id)objectAtIndex:(int)index; Unless the method has the word “copy” in it, if the object already exists, you get a
pointer to it. If the object does not already exist (like the 3 examples above), then you’re creating.
Using class methods to create objects NSString’s + (id)stringWithFormat:(NSString *)format, ... UIButton’s + (id)buttonWithType:(UIButtonType)buttonType; NSMutableArray’s + (id)arrayWithCapacity:(int)count; NSArray’s + (id)arrayWithObject:(id)anObject;
Allocating and initializing an object from scratch Doing this is a two step process: allocation, then initialization. Both steps must happen one right after the other (nested one inside the other, in
fact). Examples: NSMutableArray *stack = [[NSMutableArray alloc] init]; CalculatorBrain *brain = [[CalculatorBrain alloc] init];
About Allocating Heap allocation for a new object is done by the NSObject class method + (id)alloc It allocates enough space for all the instance variables (e.g., the ones created by
@synthesize).
About Initializing Classes can have multiple, different initializers (with arguments) in addition to plain
init. If a class can’t be fully initialized by plain init, it is supposed to raise an exception in
init. NSObject’s only initializer is init.
Ways of creating objects –cont.
More complicated init methods If an initialization method has arguments, it should still start with the four letters init Example: - (id)initWithFrame:(CGRect)aRect; // initializer for UIView UIView *myView = [[UIView alloc] initWithFrame:thePerfectFrame];
Examples of multiple initializers with different arguments From NSString: - (id)initWithCharacters:(const unichar *)characters length:(int)length; - (id)initWithFormat:(NSString *)format, ...; - (id)initWithData:(NSData *)data encoding:(NSStringEncoding)encoding;
Classes must designate an initializer for subclassers This is the initializer that subclasses must use to initialize themselves in their designated
initializer.
Static typing of initializers For subclassing reasons, init methods should be typed to return id (not statically typed) Callers should statically type though, e.g., MyObject *obj = [[MyObject alloc] init];
Ways of creating objects –cont.
Creating you own init
Creating your own initialization methodSuper initializer can return nil if it failed to
initialize.Example ---.m file@implementation MyObject- (id)init{ self = [super init]; // call our super’s designated initializer if (self) { // initialize our subclass here } return self;}
@end
Intro to Objective-C Syntax:Classes In Java, students can define and implement a class in a
single .java file. In C++, students define a class and methods in a .h header
file and implement the methods in a .c file. In Objective-C, students define a class and its methods in
a .h header file and implement the methods in a .m file.
Circle.hCircle.m
include
Intro to Objective-C Syntax:Classes
@interface Circle : NSObject { // instance variables double radius = 1.0;}
// Class methods+(double) getPi;
// Instance methods-(double) getArea;
-(void) setRadius:(double) r;
@end
Circle.h
Keyclass namesuperclassreturn type
method nameparameter typeparameter name
Optional parameter name
#import "Circle.h"
@implementation Circle
+(double) getPi { return 3.14159265; }
-(double) getArea { double pi = [Circle getPi]; return pi * radius * radius;}
-(void) setRadius:(double) r { radius = r;}
@end
Circle.m
#import "Circle.h"
// Non Objective-C function; program originint main() {
@autoreleasepool { Circle *mycirc = [[Circle alloc] init]; [mycirc setRadius:3.0]; double area = [mycirc getArea]; double pi = [Circle getPi]; return 0; }}
Main.m
Classes --- rememberHave both definition file and implementation
file : classname.h and classname.m
Prototyping methodsWhen declaring or implementing functions
for a class, they must begin with a + or -+ indicates a “class method” that can only be
used by the class itself. In other words, they’re for private functions ---like static functions in other languages.
- indicates “instance methods” to be used by the client program (public functions) –invoked on objects/instance of class
Class Declaration (Interface)#import <Cocoa/Cocoa.h>@interface Node : NSObject {
Node *link;int contents;
}+(id)new;-(void)setContent:(int)number;-(void)setLink:(Node*)next;-(int)getContent;-(Node*)getLink;@end
node.h
Class is Node who’s parent is NSObject
{ class variables }
+/- private/public methods of Class
Class variables are private
Class Definition (Implementation)#import "node.h”@implementation Node+(id)new
{ return [Node alloc];}-(void)setContent:(int)number
{contents = number;}-(void)setLink:(Node*)next {
[link autorelease];link = [next retain];
}-(int)getContent
{return contents;}-(Node*)getLink
{return link;}@end
node.m
Like your C++ .cpp file
>>just give the methods here
Creating class instancesClassName *object = [[ClassName alloc] init];
OR
ClassName *object= [[ClassName alloc] initWith*];
Destroying a classobject = nil;
The underlying system will take care of removing the object from memory for you automatically.
Note: a lot of programs don’t explicitly set objects to nil but, is an option for you.
Like NULL in C ++
Like null in Java
Do you need to test for nillif (object == nill) //or if (object){ //do whatever }
Actually, in Objective-C if an objects is nil and you send a message (method call) to it does nothing….however, if you are expecting results and try to use them you could get in trouble –so checking in this case is important.
Setting values for class variables of an object ---- THROUGH methods
ClassName *object = [[ClassName alloc] init];
[object setXXXMethod:value1];
[object setYYYYMethod:value2];
Two kinds of methods – calss and instance methodsClass Method call is like a STATIC method –
call on the class itself Example for class NSDate –has class method “date” that will
return pointer to an instance of NSDate associated with current date
NSDate *now = [NSDate date];
Instance method is like normal function – call
on an object Example for class NSDate –has instance method
“timeIntervalSince1970 ” that will return seconds of the date object since 1970double seconds = [now timeIntervalSince1970];
Method calls uses “Message syntax”
[receiver message][receiver message:argument][receiver message:arg1 andArg:arg2]
Example of a Class method to construct and new object
NSDate *now = [NSDate date];
More TerminologyMessage expression
[receiver method: argument]
Message[receiver method: argument]
Selector[receiver method: argument]
MethodThe code selected by a message
Message/Method call with multiple arguments[ Object methodp1:v1 methodp2:v2 methodp3:v3]
What is the actual method name? It is (yes it is odd!) methodp1:methodp2:methodp3
ExampleNSCalendar *cal = [NSCalendar currentCalendar];NSUInteger day = [cal ordinalityOfUnit:NSDayCalendarUnit
forDate:now];
What is the name of the method ? It is ordinalityOfUnit:forDate
Nesting Method call[[ Object method1] method 2]method 1 executed first and on the results
method 2 is executed
Example without nestingNSCalendar *cal = [NSCalendar currentCalendar];NSUInteger day = [cal ordinalityOfUnit:NSDayCalendarUnit forDate:now];
Example WITH nestingNSUInteger day = [[NSCalendar currentCalendar] ordinalityOfUnit:NSDayCalendarUnit forDate:now]
Some arbitrary examplesPerson *voter; //assume this exists[voter castBallot];
int theAge = [voter age];[voter setAge:21];
if ([voter canLegallyVote]) {// do something voter-y}
[voter registerForState:@"CA“ party:@"Independant"];
NSString *name = [[voter spouse] name];
Accessor MethodsTwo kinds: setter methods and getter
methods -- used to set and get instance variables.
Example Person.h@interface Person : NSObject
{ //two instance variables
float heightInMeters; int weightInKilos;}
- (void)setHeightInMeters:(float)h; //setter instance method - (void)setWeightInKilos:(int)w; //setter instance method - (void)weightInKilos; //getter instance method - (void)heightInMeters; //getter insance method - (float) bodyMassIndex; //instance method @end
NOTE: the convention of naming the setter methods as setVariableName
NOTE: the convention of naming the getter methods same as the variable they access
Accessor MethodsExample Person.m@implementation Person
- (float) heightInMeters { return heightInMeters; }
- (int) weightInKilos { return weightInKilos; }
- (void) setHeightInMeters:(float)h { heightInMeters = h; }
- (void) setWeightInKilos:(int)w { weightInKilos = w;}
- (float) bodyMassIndex { return weightInKilos / (heightInMeters * heightInMeters); }
@end
Lets use our Accessor MethodsExample main.mInt main(int argc, const char * argv[]){ @autoreleasepool { //Create an instance of Person Person *person = [[Person alloc] init]; //Give instance variables some values
[person setWeightInKilos:96]; [person setHeightInMeters:1.8];
//Call bodyMassIndex method float bmi = [person bodyMassIndex]; //print out NSLog(@”person (%d, %f) has a BMI of %f”, [person weightInKilos], [person heightInMeters],
bmi);
NOTE: %f mean insert float value, %d is an integer value --- same as you see in printf for C
Properties --simple way to create accessor methodsDeclare in one line the getter and setter
methods for a variableExample -- new Person.h@interface Person : NSObject
{ //two instance variables
float heightInMeters; int weightInKilos;}
@property float heightInMeters; //will create setter and getter method for this var
@property float weightInKilos; //will create setter and getter method for this var
- (float) bodyMassIndex; //instance method @end
In Person.h add @property
Properties --just have the @property Declare in one line the getter and setter
methods for a variableExample -- new Person.h@interface Person : NSObject
{
//don’t need to declare the variables here // ---they are done with @property
} @property float heightInMeters; //will create setter and getter method for this
var @property float weightInKilos; //will create setter and getter method for this
var - (float) bodyMassIndex; //instance method @end
Properties --continuedUse @synthisize annotationnew Person.m#import “Person.h”@implementation Person
@synthesize heightInMeters, weightInKilos;
- (float) bodyMassIndex { return weightInKilos / (heightInMeters * heightInMeters); }
Now in .m file must add @synthesize annotation
Do not need to create the methods
Properties can take paramenters@property (a1,a2,*) varExample @property (nonatomic, readonly, strong) NSString *itemName;
nonatomic / atomic = dealing with threading nonatomic = (YOU USE THIS FOR IOS), not thread-safe
NOTE: no problem if this is UI code because all UI code happens on the main thread of the application.
atomic = (don’t do this for iOS), thread safe, default
readwrite/readonly readwrite= default value, declares both a setter and a getter. readonly =means only create setter method.
weak/strong/assign = dealing with memory management strong= strong reference to object stored in variable –see ARC weak = weak reference to object stored in variable –see ARC assign = default for variables that are primitive data types
Keyword --selfself is like “this” in other OOP
languages
//some code inside a method of a classfloat h = [self heightInMeters]; //method calss to getter for the variable
heightInMeters
//another example a method in a class that adds itself (object) to an array that is passed
-(void) addYourselfToArrayNSMutableArray *) theArray{ [theArray addObject:self]; }
InheritenceIn .h file
@interface ClassName : ParentClass{ //class variables}
//methods
@end
Example of InheritanceCreate class Employee that has Person as parent
and adds class variable of an employee id
Employee.h file#import “Person.h”
@interface Employee : Person{ int employeeID;}@property int employeeID; //remember short cut to declare accessor
methods // for employeeID class variable
@end
Child classCan access Parent’s methods and variables
Overriding methods//Employee .m file//override the #import “Employee.h”@implementation Employee
@synthesize employeeID; //remember this genearteds the setemployeeID() and employeeID() methods
- (float) bodyMassIndex //overridden method of previous Person parent class{ return 19.0; }
@end
super = keyword to mean parent class
- (float) bodyMassIndex //overridden method of previous Person parent class{ float normalBMI = [super bodyMassIndex] ; //first call Person’s
bodyMassIndex method return normalBMI*0.9; }
Instance variables typically in one of 4 categoriesPrimitive data types
int age; float number;
Object-type attributes NSString myName; NSNumber
To-one relationship = point to a single “complex” object Employee top_Employee; Person spouse;
To-many relationships = these are collections (objects or data)
NSMutableArray *friends; NSArray *emails;
Class Example with some different “kinds” of instance vars#import “Person.h”
@interface Employee : Person{ int employeeID; //primitive data NSString *lastName; //object type Person *spouse; //To-one more complex
object NSMutableArray *children; //To-many collections}//method declarations *****
@end
Employee.h
IMPORTANTHave you noticed that objectinstance variables are alwaysPointers to objects.
STOP: huh? Variables are always pointers to ObjectsObjects don’t live inside other objects.You only points from one object to another
MePerson -> spouse (another Person)
Result: you end up with a lot of distinct objects in your program’s memory
Luckily we have Automatic Reference Counting for our iOS programs to take care of memory leaking and getting rid of no longer needed objects!!! Yes!
Object TypingSuppose have Vehicle class and child Ship class
@interface Vehicle- (void)move;@end
@interface Ship : Vehicle- (void)shoot;@end
Ship *s = [[Ship alloc] init];[s shoot];[s move];Vehicle *v = s;[v shoot]; //THIS CAUSES a COMPILER WARNING –but not a runtime error
Object TypingSuppose have Vehicle class and child Ship
class
id obj = ...;
[obj shoot]; //This is NOT a compiler warning
The compiler knows that the method shoot exists,•possible that obj might respond to it --- NO compiler warning•not typed obj enough for the compiler to be sure it’s wrong.
Will crash at runtime if obj is not a Ship(unless is an object of some other class that implements a shoot method).
Object TypingSuppose have Vehicle class and child Ship
class
id obj = ...;
[obj someMethodNameThatNoObjectAnywhereRespondsTo];has never heard of this method.
COMPILER WARNING
Object TypingSuppose have Vehicle class and child Ship
class
NSString *hello = @”hello”;[hello shoot];
The compiler knows that NSString objects do not respond to shoot.crash at runtime.
COMPILER WARNING
Object TypingSuppose have Vehicle class and child Ship
class
NSString *hello = @”hello”;
Ship *helloShip = (Ship *)hello; [helloShip shoot];
We are “casting” here.The compiler thinks we know what we’re doing.
No compiler error as helloShip is thought to be a ship.. HOWEVER, it isnot so, RUNTIME ERROR
NSObjectBase class for pretty much every object in the
iOS SDKMethods
- (NSString *)description is a useful method to override (it’s %@ in NSLog()).
- (id)copy not all objects implement mechanism (raises
exception if not)
- (id)mutableCopy not all objects implement mechanism (raises
exception if not)
linkList class#import "linkList.h"
@implementation linkList
+(id)new
{return [linkList alloc];}
-(void)insert:(int)value {
id temp = [Node new];
[temp setContent:value];
[temp setLink:head];
head = [temp retain];
[temp release];
}
-(void)append:(int)value { id last = [head getLink]; while ([last getLink] != nil) {last = [last getLink];} id temp = [Node new]; [temp setContent:value]; [last setLink:temp]; [temp release];}-(void)remove { id temp = head; head = [head getLink]; [temp release];}-(int)getValue { return [head getContent];}@end
linkList.m
Class linkList is child of previous Node class
Stack class#import "linkList.h”
@interface Stack : linkList
{}
+(id)new;
-(void)push:(int)value;
-(int)pop;
@end
#import "stack.h”
@implementation Stack+(id)new {return [Stack alloc];}
-(void)push:(int)value {[self insert:value];}
-(int)pop { int ret = [self getValue]; //getValue method of parent linkList [self remove]; //remove method of parent linkList return ret;}
@end
stack.h stack.m
Self is like the C++/Java word this.
Remember alloc creates the object in memory
Example: main.m#import "stack.h”int main(){
Stack *s = [Stack new];[s push:1];[s push:2];printf("%d\t", [s pop]);[s push:3];printf("%d\t", [s pop]);printf("%d\t", [s pop]);[s release];return 0;
}
$ gcc -x objective-c node.m linkList.m stack.m main.c -framework Cocoa -o stackTest
$./stackTest
2 3 1
main.c
new is the same as in C++/Java
Note only need to import “stack.h” because stack imports LinkList.h which imports Node.h which imports cocoa.h