Cocoa for Web Developers

Introduction to OS X development with Cocoa … and how web developers can cheat George Brocklehurst http://georgebrock.com @georgebrock on Twitter

Before we start… Have you done any… HTML? Javascript? PHP? Any object oriented programming? C?

What is Cocoa? Framework for Mac OS X and iPhone Heavily MVC focused Usually written in Objective-C Can also be written in Python or Ruby

Getting Started You will need: Apple’s Xcode Tools Available from: http://developer.apple.com/technology/xcode.html Your OS X install DVDs

Objective C Syntax: Classes Declaring a class interface (.h file) @interface MyClass : NSObject { int anInteger; } - (void)doStuff; @end

Objective C Syntax: Classes Declaring a class interface (.h file) @interface MyClass : NSObject { int anInteger; } - (void)doStuff; @end Interface only here!

Objective C Syntax: Classes Declaring a class interface (.h file) @interface MyClass : NSObject { int anInteger; } - (void)doStuff; @end Class name

Objective C Syntax: Classes Declaring a class interface (.h file) @interface MyClass : NSObject { int anInteger; } - (void)doStuff; @end Parent class

Objective C Syntax: Classes Declaring a class interface (.h file) @interface MyClass : NSObject { int anInteger; } - (void)doStuff; @end Members

Objective C Syntax: Classes Declaring a class interface (.h file) @interface MyClass : NSObject { int anInteger; } - (void)doStuff; @end Methods

Objective C Syntax: Classes Implementing a class (.m file) #import “MyClass.h” @implementation MyClass (void)doStuff { // Do stuff here } @end

Objective C Syntax: Classes Implementing a class (.m file) #import “MyClass.h” @implementation MyClass (void)doStuff { // Do stuff here } @end Interface

Objective C Syntax: Classes Implementing a class (.m file) #import “MyClass.h” @implementation MyClass (void)doStuff { // Do stuff here } @end Start class implementation

Objective C Syntax: Classes Implementing a class (.m file) #import “MyClass.h” @implementation MyClass - (void)doStuff { // Do stuff here } @end Methods with bodies

Objective C Syntax: Methods -(void)myMethod:(int)arg In other languages, might be: function myMethod(arg)

Objective C Syntax: Methods - (void)myMethod:(int)arg Can be either: + for a class method - for an instance method Method scope

Objective C Syntax: Methods -( void )myMethod:(int)arg Can be any valid data type, including: void returns nothing id a pointer to an object of any class NSString* a pointer to an NSString BOOL a boolean ( TRUE , FALSE , YES or NO ) Return type

Objective C Syntax: Methods -(void) myMethod: (int)arg Colons precede arguments, but are considered part of the method name Method name

Objective C Syntax: Methods -(void)myMethod: (int)arg Come after or within the method name For multiple arguments: -(void)myMethod: (int)arg andAlso: (int)arg2 (Method name is “myMethod:andAlso:”) Argument type Argument name

Objective C Syntax: Methods -(void)myMethod:(int)arg1 andAlso:(int)arg2; How to call this method: [myObject myMethod:10 andAlso:20]; In other languages this might be: myObject->myMethod(10, 20); //or myObject.myMethod(10, 20);

Objective C Syntax: Properties New short hand in Objective-C 2.0 (Xcode 3 / Leopard) Access class members without writing getters and setters Convenient, but nasty difficult to remember syntax

Objective C Syntax: Properties In the class interface (with methods): @property(copy, readwrite) NSString *propertyName; In the class implementation: @synthesize propertyName; To access: myInstance.propertyName = @”Foo”;

Objective C Syntax: Properties In the class interface (with methods): @property( copy , readwrite) NSString *propertyName; In the class implementation: @synthesize propertyName; To access: myInstance.propertyName = @”Foo”; Storage method: assign , retain or copy

Objective C Syntax: Properties In the class interface (with methods): @property(copy, readwrite ) NSString *propertyName; In the class implementation: @synthesize propertyName; To access: myInstance.propertyName = @”Foo”; Access permissions: readwrite or readonly

Objective C Syntax: Properties In the class interface (with methods): @property(copy, readwrite) NSString *propertyName; In the class implementation: @synthesize propertyName; To access: myInstance.propertyName = @”Foo”; Can add other things: nonatomic , getter=… and setter=…

Objective C Syntax: Properties In the class interface (with methods): @property(copy, readwrite) NSString *propertyName ; In the class implementation: @synthesize propertyName; To access: myInstance.propertyName = @”Foo”; Property variable declaration, must also be declared as a class member

Objective C Syntax: Properties In the class interface (with methods): @property(copy, readwrite) NSString *propertyName; In the class implementation: @synthesize propertyName; To access: myInstance.propertyName = @”Foo”; Tell Objective-C precompiler to make getter & setter

Objective C Syntax: Properties In the class interface (with methods): @property(copy, readwrite) NSString *propertyName; In the class implementation: @synthesize propertyName; To access: myInstance . propertyName = @”Foo”; Sensible syntax! Yay!

Objective C Syntax: Selectors SEL callback = NULL; callback = @selector(myMethod:andAlso:); Like function pointers Useful for callback type behavior

Objective C Syntax: Selectors SEL callback = NULL; callback = @selector(myMethod:andAlso:); Like function pointers Useful for callback type behavior Data type for selectors

Objective C Syntax: Selectors SEL callback = NULL; callback = @selector( myMethod:andAlso: ) ; Like function pointers Useful for callback type behavior Macro to create selector

Objective C Syntax: Strings NSString *myString; myString = @”This is a string” ; Note the @ prefix Tells the Objective-C precompiler to instantiate an NSString instead of just creating a C string (aka. A nasty character array)

Managing Memory Easier than vanilla C, honest! Reference counting Increment with retain , decrement with release Rule of thumb: release anything you alloc , copy or retain

Managing Memory: Example NSString *str; str = [NSString alloc ]; //1 [str retain ]; //2 [str release ]; //1 [str release ], str = nil; //0

Managing Memory: Autorelease [str autorelease]; This will automatically release an object when it’s finished with Another rule of thumb: [NSThing thingWith:…] returns an autoreleased instance [[NSThing alloc] initWith:…] needs manually releasing

Wasn’t there something about cheating?! WebKit is part of Cocoa Can build your UI with HTML, CSS and Javascript and only use Objective-C when you really need to

K, Thx, Bai! George Brocklehurst http://georgebrock.com @georgebrock on Twitter

Cocoa for Web Developers

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