iPhone Development Crash Course

By Dylan Harris9-19-11

For the tutorials

• Xcode 3 or 4 working and installed?• Right now only a few ways to get Xcode 4– Upgrade to Lion, get of app store for free– Sign up for $100 developer account

• Maybe it will become free when iOS 5 releases?

Topics today

• iPhone Development Overview• Objective-C Language Basics• Custom classes• Memory management basics• Tutorials throughout

Getting help

• API & Conceptual Docs– Found in Xcode under help menu– Also found on developer.apple.com

• Class header files• The Internet– Stack Overflow, blogs, iTunes U(Stanford classes)

Model-View-Controller

• iPhone dev uses the MVC design pattern• Model: Manages the app state and data• View: Presents the Model to the user in an

appropriate interface• Controller: Middleman between the Model

and the View

Cocoa Frameworks

• Foundation– Check out object docs• NSString

– Objective-C string constant: @”This is a string”

• NSArray, NSDictionary, NSSet• Their “mutable” counterparts

• UIKit– User interface elements

Objective-C

• Strict superset of C– Mix C with ObjC

• Single inheritance– Classes inherit from one and only one superclass

• Protocols define behavior that cross classes• Dynamic runtime– All variables declared on heap

• Loosely typed, if you want

Syntax Additions

• New types– id: anonymous object, allows for loose typing– Class: a class is also an object– Selector: like a function pointer

• Syntax for message expressions– [receiver message:argument];

Message Syntax

• [receiver message]• [receiver message:argument]• [receiver message:arg1 andArg:arg2]

An example

• Person *person; //assume exists• [person walk];

– (void)walk;

• int theAge = [person age];– (int)age;

• [person setAge:25 andHeight:60];– (void)setAge:(int)age andHeight:(int)height;

• NSString* spouseName = [[person spouse] name];– (Person*)spouse– (NSString*)name

Terminology

• Message expression– [receiver method: argument]

• Message – [receiver method: argument]

• Selector– [receiver method: argument]

• Method – The code selected by a message

Classes and Instances

• Both classes and instances are objects• Classes are messaged to create instances• Instances respond to instance methods– (id)init;– (void)walk;

• Classes respond to class methods+(id)alloc;+(Person*)sharedPerson;

• You can ask an object about it’s class(introspection)

Dot Syntax

• Convenient shorthand for invoking accessor methods• float height = [person height]; • float height = person.height;• [person setHeight:newHeight]; • person.height = newHeight;

• Follows the dots...• [[person child] setHeight:newHeight];• // exactly the same as person.child.height = newHeight;

Tutorial

• Hello World

• Follow along if Xcode and iPhone SDK installed• Use Simulator

Null Object Pointer

• Test for nil explicitly– if (person == nil) return;

• Or implicitly– if (!person) return;

• Can use in assignments and as arguments if expected– person = nil; – [button setTarget: nil];

• Sending a message to nil? Perfectly fine– person = nil; – [person walk];

BOOL typedef

• When ObjC was developed, C had no boolean type (C99 introduced one)

• ObjC uses a typedef to define BOOL as a type– BOOL flag = NO;

• Macros included for initialization and comparison: YES and NO (TRUE and FALSE are also typedef)– if (flag == YES) – if (flag) – if (!flag) – if (flag != YES)– flag = YES;– flag = 1;

Custom classes

• Inherit from NSObject• .h is header• .m is implementation

Header file interface#import <Foundation/Foundation.h>

@interface Person : NSObject { // instance variables NSString *name; int age;}

// method declarations - (NSString *)name; - (void)setName:(NSString *)value;

- (int)age; - (void)setAge:(int)age;

- (BOOL)canLegallyVote;

@end

Getter/setter methods#import "Person.h”

@implementation Person

- (int)age { return age;} - (void)setAge:(int)value { age = value;}

//... and other methods @end

Action methods#import "Person.h”

@implementation Person

- (BOOL)canLegallyVote { return ([self age] >= 18);}

@end

• Note the “self” object, same as this pointer in C++• Can also call “super” to access methods in the superclass

– [super dosomething];

Object creation

• Two step process– Allocate memory to store the object– Initialize the object state

• [[Person alloc] init] returns a new Person• Can have other init methods– [[Person alloc] initWithAge:25];

Reference Counting

• Every NSObject has a retain count• +alloc and -copy create objects with retain count of 1• -retain increments retain count• -release decrements retain count• Retain count reaches 0, -dealloc automatically called

and object is destroyed

Person *person = [[Person alloc] init];[person doSomething];[person release];

Reference counting in action

Person *person = [[Person alloc] init]; Retain count begins at 1 with +alloc[person retain]; Retain count increases to 2 with -retain[person release]; Retain count decreases to 1 with -release[person release]; Retain count decreases to 0, -dealloc automatically called

Autorelease

• Example: returning a newly created object-(NSString *)fullName { NSString *result; result = [[NSString alloc] initWithFormat:@“%@ %@”, firstName, lastName];

[result autorelease]

return result;}

Method Names & Autorelease• Methods whose names includes alloc, copy, or new return a retained

object that the caller needs to release

NSMutableString *string = [[NSMutableString alloc] init];// We are responsible for calling -release or -autorelease[string autorelease];

• All other methods return autoreleased objects

NSMutableString *string = [NSMutableString string];// The method name doesn’t indicate that we need to release it, so don’t

• This is a convention- follow it in methods you define!

Properties

• Shortcut for implementing getter/setter methods

Defining Properties#import <Foundation/Foundation.h>

@interface Person : NSObject { // instance variables NSString *name; int age;}

// method declarations - (NSString *)name; - (void)setName:(NSString *)value;

- (int)age; - (void)setAge:(int)age;

@end

Defining Properties#import <Foundation/Foundation.h>

@interface Person : NSObject { // instance variables NSString *name; int age;}

// method declarations @property (copy) NSString* name;@property int age;

@end

Synthesizing Properties@implementation Person

- (int)age { return age;}

- (void)setAge:(int)value { age = value;}

Synthesizing Properties@implementation Person

@synthesize age;

- (void)setAge:(int)value { age = value; // now do something with the new age value...}

• Can mix and match synthesized and implemented properties– Synthesize age, but implement setAge– Getter method still synthesized

Property Attributes

• Read-only versus read-write

@property int age; // read-write by default @property (readonly) BOOL canLegallyVote;

• Memory management policies (only for object properties)

@property (assign) NSString *name; // pointer assignment @property (retain) NSString *name; // retain called @property (copy) NSString *name; // copy called

Tutorial

• Follow along if Xcode and iPhone SDK installed• Use Simulator

Comments/Questions?