An Introduction to Android for iOS Developers

Simon D. LevyCSCI 251

12 May 2014

DISCLAIMER ...

Android vs. iOS: Consumer

Perspective

(worldwide)

forbes.com

forbes.com

UnixNon-Unix

http://en.wikipedia.org/wiki/File:Unix_history-simple.svg

Consumer Perspective:

Devices

http://www.digitaltrends.com/

http://www.cnet.com/

http://www.cnet.com/

Samsung T9000

Google Project Ara

Developer Perspective:

Distribution Model

Walled Garden

Curated Computing

Wild West!

Wild West?

http://en.wikipedia.org/wiki/Walled_garden_%28technology%29

Fee Structure

Getting your app onto your device: Provisioning

Getting your app onto your device: Provisioning

The Power of Open Standards

Reverse Engineering

Developer Perspective:

OS

http://developer.apple.com

http://en.wikipedia.org/wiki/Android_os

Developer Perspective:

IDE

Ancestry: NeXT

Developer Perspective:Language

CSmalltalk

Objective-CC++

Simula

1960

1970

1980

1990

2000

Java

Memory AllocatiomC++: Explicit deallocaction

void mymethod(){

Circle * circ = new Circle(3,4,2);…

delete circ;}

Memory AllocatiomJava: Garbage-collected

void mymethod(){

Circle circ = new Circle(3,4,2);…

} // circ automatically deallocated now

Memory Allocatiom● Objective-C: Reference counting (“semi-automatic”

garbage collection)

NSString* s = [[NSString alloc] init]; // Ref count is 1[s retain]; // Ref count is 2 - silly // to do this after init[s release]; // Ref count is back to 1[s release]; // Ref count is 0, s is freed

http://stackoverflow.com/questions/6578/understanding-reference-counting-with-cocoa-and-objective-c

● Xcode (4.2 and later) provides Automatic Reference Coutning (ARC), making this largely unnecessary

Inheritance● C++: Multiple inheritance

class Apple : Fruit, Edible{

};

● Experienced programmers avoid this, using composition (has-a) instead of inheritance (is-a).

Inheritance● Java: Single inheritance + interfaces

class Apple extends Fruit, implements Edible{

}

Inheritance● Objective-C: Single inheritance + protocols

@interface MyClass : NSObject <MyProtocol>

...

@end

https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithProtocols/WorkingwithProtocols.html

Method Invocation C++, Java

● Invoke an object's method● “Tight” association between method

and class ● Compiler makes sure that class

implements method

circ.move(-3,5);

Method InvocationObjective-C

● Send a message to an object● “Looser” association between method

and class ● Object can ignore message (runtime

constraints; programmer didn't implement method)

[circ moveX:-3 andY:5];

Reflection

● Java: We can query the type (class) of an object at runtime:

System.out.println(c.getClass());

Reflection● Objective-C: We can also check which

messages the object responds to:

http://stackoverflow.com/questions/4574465/objective-c-respondstoselector-question

if ([c respondsToSelector:@selector(move:)]){

}

if([c isKindOfClass:[NSString class]]){

}