iPhone development from a Java perspective (Jazoon '09)

Development for the iPhone from a Java PerspectiveThe Tools, The Language, The Experience

Ognen Ivanovski

Netcetera

9140

2

3

Background

> Software Architect; @Netcetera since 2001

> 2000 - present: Java (enterprise, web, swing, RCP)

> 2008 - present

– Mobile Development: Android, iPhone OS

– Technical Lead for Wemlin

4

> iPhone App

> Covers the Zürich greater area

> See departure times for public transport

> Completely offline app

> Database holds roughly 1.2M records

– but it’s fast

> http://mobile.netcetera.ch/wemlin

5

Switching

> Team of four developers

> Published 1.0 of Wemlin (then Tramdroid) on October 3rd 2008

> 1 - 3 weeks adaptation time

> 1st internal build after 4 weeks

6

New Priorities

> Performance

> Start-up time

> UI

> Simplicity

7

F.A.Q.

> No, you can’t use Eclipse for development

> No, you cannot use Java either

> Yes, you do need a Mac (Intel based)

> iPhone SDK

– http://developer.apple.com/iphone

– xCode enhanced with iPhone specific frameworks and tools

– Registration is free, you can download, develop & test in the simulatora fee is required if you want to test on the device and to distribute

8

The Stack

> OS X (FreeBSD, Mach 3)

> libc (POSIX)

> Core Services

> Objective-C

> CocoaTouch

9

First Impressions: Toolbox

10

First Impressions: xCode

> Yes, you are going to miss Eclipse

– Refactoring support in infancy but progressing

– SCM support is quite poor (NetBeans is comparable)

– Code browsing is poor

– No compile as you type

– Takes some will to switch

11

xCode: What’s Interesting

> Multi-window support

> Great documentation browser

> Extensive documentation (1.5GB)

> Built on top of OpenSource technologies

– gcc

– gdb

– Unix scripts to enhance (stdin, stdout)

– in any scripting language

12

Interface Builder

> Integral part of the SDK

> Probably the second visual editor I actually use(d)

> Integrates with xCode

– information about classes and their features

– Outlets, actions, connections

> NIB / XIB files

– very similar to Java .ser (serialized) files used in the early days of Swing by IDEs

Forte 4 Java

13

First Impressions: Build system

> The same build system is used from both the IDE and command line

– xcodebuild

– one project file

– low build maintenance cost

> You don’t actually miss maven much

– Builds are easy to set up and maintain

– Advice: don’t reinvent the wheel (use the standard tool box)

> Frameworks

– no central repository

– no out of the box “materialization” of frameworksreliance on shared drives to achieve the goal

14

First Impressions: Instruments

> It’s Just GREAT

> It’s based on DTrace

> DTrace is present on the devices too

> Almost real-time profiling & analysis both in Simulator and device

– Just “attach” on a running process

15

Objective-C / Java connection?

> OpenStep API specification

– Developed jointly by NeXT and Sun Inc. @1993-1994

– Direct predecessor to Cocoa and CocoaTouch

> Java (probably) was strongly influenced by Objective-C

– http://www.virtualschool.edu/objectivec/influenceOnJava.html

> At least a common Smalltalk heritage

16

One Big Difference

No Source Code

17

Should I learn it?

> NeXT -> didn’t reach a wide audience

> Macs too (more or less) -> 8% world PC market

but

> Installed base of OS X including iPhones and iPod touches:

– grown from 25M to nearly 75M in the last 2 years

> The platform has reached an incredible number of developers and users in the last 2 years

> Customers asked for it :-)

18

Diving Deeper: The Platform

19

Devices

> iPhone

> iPhone 3G

> iPod Touch

> iPod Touch 2nd generation

> iPhone 3GS

> ARM11 ~ 400 MHz

> 128MB RAM (~50MB available to an app)

> Hardware Graphics Accelerator

> Slightly faster

> ARM Cortex V8 ~ 600 MHz

> 256MB RAM

20

Objective-C

> Shared (Smalltalk) heritage with Java

– compiled

– late bound

– single inheritance

– one root class

– Pass-by-reference for objects, pass-by-value for “primitives”

– camelCase convention

21

Syntax

> Strict superset of ANSI C

> Object syntax is borrowed from Smalltalk

– [object method] instead of

– object.method()

– [dictionary setValue:aValue forKey:key]

– [location setDistanceInMeters:3 from:zurich]

– [location setDistanceInKiloMeters:3 from:zurich]

– NSString *s = [NSString stringWithFormat:@"height %2i", height];

22

Type System

> Dynamically typed, late bound

– Sending messages opposed to method invocation

– messages (selectors) have a type and can be passed around

> Type annotations are just “hints” to the compiler, can be added after the fact

– type id is like Object in Java (every object is of type id)

– you can send any message to an object of type id

> “object variable declaration”:

– NSString *variable = ...;

– id variable = ...; (id is like void *)

23

Nil

> You can send any message to the nil object

– It will always succeed

> Return value is always with negative semantics– depends on the method signature / call site

– [nil isCreated] will return NO

– [nil numberOfCopies] will return 0

> Is this good?

24

Namespace handling

> There isn’t any

> Prefixes are used instead (2 to 4 letters) on classes and global functions

– NSString (Foundation, historical, for NextStep)

– UIView (UI = UIKit)

– CLLocation (CL = CoreLocation)

25

Classes: MyClass.h

#import <Foundation/Foundation.h>

@interface MyClass : NSObject {

int age;

NSString *name;

}

@end

26

Classes: MyClass.m

#import "MyClass.h"

@implementation MyClass

@end

27

Methods

#import <Foundation/Foundation.h>

@interface MyClass : NSObject {

int age;

NSString *name;

}

- (id)init;

- (id)initWithName:(NSString *)name;

+ (id)myClassWithName:(NSString *)name age:(int)age;

- (NSString *)name;

@end

28

Methods: implementation

#import "MyClass.h"

@implementation MyClass

+ (id)myClassWithName:(NSString *)name age:(int)age

{

return [[MyClass new] autorelease];

}

- (NSString *)name

{

return name;

}

@end

29

Selectors

> The message

> Dynamic invocation

SEL notification = @selector(jobDone:);id callback = // ...;[callback performSelector:notification withObject:result];

30

Instantiation

MyClass *instance = [[MyClass alloc] init];

// same as

MyClass *instance = [MyClass new];

31

Protocols

#import <Foundation/Foundation.h>

@protocol StateHandling

- (void)handleState:(id)state;

@optional

- (id)provideState;

@end

#import "StateHandling.h"

@interface MyClass <StateHandling> : NSObject {

// ...

}

// ...

@end

32

Protocols

id <StateHandling> handler = // ...;

[handler handleState:aState];

if ([handler respondsToSelector:@selector(provideState)]) {

id newState = [handler provideState];

}

33

Categories

> Every existing class can be extended with new methods using categories

– open classes

– limitation: no instance variables can be added

> Used quite often

34

NSObject

> The main root class

> Methods:

– class

– superclass

– description (toString)

– hash

– isEqual:

– isKindOfClass:

35

Reflection

id anObject;

[anObject respondsToSelector:@selector(handleTouch:)][anObject isKindOfClass:[UITableView class]][anObject isMemberOfClass:[UITableView class]][anObject conformsToProtocol:@protocol(Copying)]

> C based API (Objective-C runtime) for full blown introspection

36

Memory Management

> Manual Reference Counting

> Autorelease pools

anObject = [argumentObject retain]

[anObject release]

return [anObject autorelease]

> THE biggest issue we had and still have

– dangling pointers

37

Objective-C

> Dynamically Typed, late bound

> Semantically very similar to Java

– root class

– single inheritance

> Protocols are just like interfaces

– have optional methods

> Classes can be extended through categories

> Classes cannot be nested’

> Verbose

38

Patterns

39

Application Model

> SpringBoard

> Single Running Application

> Familiar (Swing)

> Main Thread w/ event loop

40

Key-Value Coding (KVC)

> A convention similar to the JavaBean convention

– properties

– observing

> A bit more verbose and powerful

> You get a lot for free

– automatic observer notification

– very easy to use

> Accessor Methods

[anObject setName:@"name"];

[anObject name];

[anObject isHidden];

41

Notification Center / Events

> Notification Center

– broadcast notifications

> Events

– user events

– responder chain

42

Delegate Pattern

43

Target / Action Pattern

> Interface Builder

– Outlets

– Actions

– Connections

44

MVC

> extension through inheritance

> mixed behavior and view construction

45

MVC (classic)

> views composed out of stock components in interface builder

> behavior in controllers

> connections in interface builder (outlets, actions)

46

Take Away

> A Java developer is likely to feel at his/her uncle’s house on the iPhone

> Memory management will grow some gray hairs on you

> Love thy garbage collector

> Objective-C is a unique, intoxicating mix of high-level language and raw power

> Scroll speed is important

Ognen Ivanovski http://mobile.netcetera.com

Netcetera [email protected]