Objective-C - USALmaxus.fis.usal.es/HOTHOUSE/berlin/2010/hu2010objc.pdf · Stephen G. Kochan...

Objective-Can excursus

Universidad de Salamanca

Humboldt Universität BerlinMai 2010Dr. J.R. García-Bermejo Giner

miércoles 12 de mayo de 2010

First of all...

Danke schön!


Salamanca as an Erasmus Destination

Just three short videos


Bio & paraphernalia

Dr. José Rafael García-Bermejo Giner

About the University of Salamanca

[email protected]

http://maxus.fis.usal.es/

COURSE MATERIALS - Please download these files:

http://maxus.fis.usal.es/berlin/2010/hu2010objc.pdf http://maxus.fis.usal.es/berlin/2010/programs.zip


http://www.usal.es/

http://www.usal.es/

mailto:[email protected]

mailto:[email protected]

http://maxus.fis.usal.es

http://maxus.fis.usal.es

http://maxus.fis.usal.es/berlin2010/coursematerials.zip




Contents

Contents========

A little history

The Objective-C Programming Language

Objective-C Applications


A bit of History

Objective-C===========

Bradford Cox and the Software ICs

The NeXT Story

And then Cocoa


B. Cox and Software ICs

Object-Oriented ProgrammingAn Evolutionary Approach19861991

Two main ideas

Software ICsA software-component shopping basket


The NeXT Story

Initially a hardware company BSD, Mach Kernel

NextStep and Objective-C (1990-1993)The first web server (CERN)

An interesting spin-off: WebObjects(AppleStore, iTunes Store!!)


And then Cocoa

Copland (1987)Gershwin (1994-1996)1996: Apple buys NeXTMac OS X - 2001


And then Cocoa

iPodiPod TouchiPhoneiPad - May 28th


And then Cocoa

iPodiPod TouchiPhoneiPad - May 28th

ProgrammableDevices


...end of Story

Today’s Objective-C

Mac OS X (Objective-C 2.0)

iPhone OS 4.0 (Multitasking at last!)


Objective-Can excursus (II)




Objective-C, a programming language

Bibliography - a starting point, there is more!

Stephen G. KochanProgramming in Objective-C 2.0 (2nd edition, 2009)Addison-Wesley

Aaron HillegassCocoa Programming for Mac OS X (2008)Addison Wesley

Sengan Baring-GouldTeach yourself Cocoa Touch Programming in 24 hoursSams



And now a bit of hands-on: Viele Grüße!

A program written and compiled from the Terminal

A program written and compiled from XCode


Objective-C, a programming languageA question of syntax (practice will make things clearer)

C syntax is perfectly valid - but no functions outside classes!

You can call functions from methods (frequent).You can call methods from functions (valid, less common).

Instead of the dot notation, we use the square-bracket notation.

Java Objective-Cdescriptor.method(argument); [pointer method:argument];

Methods calls can be chained

Java Objective-Cframe.getContentPane().add(x); [[obj getName] stringWithCoding:UTF8];

It is frequent to see text-based programs written in C or C++ being given a user interface by means of Objective-C.



Where is the documentation?

Of course, there are man pages.

And, XCode does have much to say.



Messages and nilThis is one important difference from C: the nil pointer is one more pointer. Messages sent to it just do nothing, return 0 and do not produce catastrophic failure of the program.

Example: MessageToNilXCode



Having Class(es)

The definition of a class is normally split into two files:

a .h or interface file a .m or implementation file.

The interface file contains

a list of instance variables (no class variables) a list of class methods (similar to static methods in Java) a list of instance methods

The implementation file contains

the #import of the interface file a list of class methods (similar to static methods in Java) a list of instance methods



Having Class(es)

Interface files look like this:

@interface NameOfClass : NameOfSuperclass <NameOfProtocol_01,...> {

// Instance variables (there are no class variables!)-(type_1) instanceVariable_1;...-(type_M) instanceVariable_N;

}

// Class and Instance methods+(type) classMethod;...-(type) instanceMethod[:(type)argument label:(type)anotherArgument...];

@end



Having Class(es)

Implementation files look like this:

#import “NameOfClass.h”@implementation NameOfClass {

// Class methods, if any+(type) classMethod {...}...// Instance methods, if any-(type) instanceMethod[:(type)argument label:(type)anotherArgument...]{...}

...

@end



Having Class(es)

And quickly, an example and our first challenge.

Write a program that shows how to build classes with attributes, methods etc.

Example: HavingClasses

Can you add an Ellipse class? It should have four attributes:xPositionyPositionsemiMajorAxissemiMinorAxis

and the same methods as Circle, Rectangle or Triangle



A word on initialization - writing good init methods

The perfect init:

-(id)init {self = [super init];if (self != nil) {

// do initializations}return (self);

}

Write a program that shows good programming practices as far as initialisation is concerned. For instance, write a random number generator with a couple of constructors, and test both of them.

Example: GoodStart: equal or different



A word on initialization - writing good init methods

The perfect init:

-(id)init {self = [super init];if (self != nil) {

// do initializations}return (self);

}

Write a program that shows good programming practices as far as initialisation is concerned. For instance, write a random number generator with a couple of constructors, and test both of them.

Example: GoodStart: equal or different

Four main points:Call the superclass initSet selfcheck selfreturn self


Objective-C, a programming languageBeing Dynamic

Types can be resolved at compile time, and also at runtime

id - An important addition to C. It is a pointer to any type of class, without loosing the class!

Why does it work? Because Objective-C classes inherit a variable called isa, of type Class, which contains the Class of the object. Hence it is possible to access methods,and also the actual name of the class to which the object belongs.

Write a program that actually shows how an id variable does not loose class information. For instance, create two classes with methods to set and get their status, and test them by assigning their pointers to an id variable.



Polymorphism

One of the characteristics of object-oriented languages: the capability to distinguish methods by examining their signatures.

Write a class with polimorphyc methods that do different things. For instance, have the class say something just once or a number of times.

Example: PolymorphXCode



Having Properties

Declaring the right access methods opens the door to Key-Value Coding.Being Dynamic showed the way to find out a class’ Class (and name).This will actually let us access variables of that class. Properties can have a few types of accessor methods:

•readonly•readwrite•copy•assign•retain•getter=name;•setter=name;•nonatomic

Write a class that has properties, define them be means of @property and @synthesize, and test the various ways to access status.



Within scope

Accessibility is regulated in a way similar to Java, by means of directives like @private, @protected, @public and @package.

Example: WithinScope

Write a program that shows how the public, protected and public attributes of a class (Student) can o cannot be accessed from another class (MrSnoop).



Gnothi seauthon, or, know thyself: key-value coding

Nota bene. There is much, much more to this. Check documentation.

Example: KnowThySelf

Write a program that accesses the attributes of a class both by means of access methods and by means of key-value coding. The program must have at least two data clases (Me and You for instance), plus another class (Know) that tests access.



Following Protocol(s)

This is the idea behind Java interfaces. Equivalent syntax is as follows:

public class JavaClass extends ItsSuperclass implements An_Interface [,...] {...}

@interface Objective_C_class : ItsSuperclass <A_protocol [,...]>@required...@optional...@end

Define a protocol and then write a class that implements it. For instance, write three classes and have them implement the same protocol. Of course,the methods in each class must adapt to the class.

Example: AccordingToProtocol

Can you add an Ellipse class that conforms to the protocol?



The benefits of inheritance

•There is just single inheritance, not multiple inheritance.

•Methods and attributes are inherited as expected.

•The super keyword permits us to use overridden methods.

•Object references NEVER loose their identity. They are compatible with other elements within the inheritance hierarchy, but they are still objects of a given class.

Write four classes that show how inheritance (and scope) works. For instance, create an inheritance hieranchy (Grandfather, Father, Sohn) and an external class (BrotherInLaw) and check access to attributes and methods.

Example: ScopesAndInheritance



Something new: Categories and Extensions

Categories are a mechanism that allows us to add new class or instance methods (but no new attributes) to the definition of a class.

Like classes, categories consist of an @interface part (in a .h file) and an @implementation part (in a .m file). The name of the category is the same as the name of the class plus an identifier for the category between parentheses. The name of the file is the name of the class, plus a “+” sign, plus the name of the category and the extension.

File: NameOfClass+NameOfCategory.h”

#import “NameOfClass.h”

@interface NameOfClass(NameOfCategory)

+(type)method:(type)argument......-(type)anotherMethod:(type)argument...

@end


Objective-C, a programming languageSomething new: Categories and Extensions

And quickly, an example. We are going to add a mechanism for saving and loading to a previous exercise.

A few caveats

No “{“ or “{“ in category definition!Extensions are inherited :)No new attributesAnonymous categories are possible (extensions)Watch naming rules!

Write a program that creates several classes and adds a category to them. The program that check the classes’ access to the methods added by the category.

Example: ShapesWithDiskAccess

Can you add a category to Shape and write the same example?


Objective-C, a programming languageException handling

Quite similar to Java; it makes use of the directives @try, @catch and @finally. There is also a @throw directive, with the usual sense.

One can throw any object, not just a derivation of NSException. However, most older frameworks will only catch derivations of NSException, hence it is a good idea to throw that kind of exception if you suspect it might have to be caught outside your code.

Write a program that catches and throws exceptions.

Example: ExceptionalBehaviour


Objective-C, a programming languageIn summary

Objective-C is an object-oriented language with some common points with Java (of which it is the predecessor).

There exists a single-inheritance mechanism (but not multiple inheritance).

There is a category-based extension mechanism.

There is a protocol-based design mechanism (interfaces).

There is an automatic mechanism for access-method creation.

There is a garbage-collection mechanism (and a manually-controlled mechanism too).

It is possible to mix method calls with C-function calls. Within reason, there is compatibility with C++.


Objective-Can excursus (III)





The Tools: XCode and Interface Builder

iPhone OS and Cocoa Touch



The Tools: XCode and Interface Builder (DEMO)

See the way an example is built, for instance TextEdit. For 1st pass, just open



Interface Builder for Cocoa Touch (DEMO)

See the way an example is built, just show the emulator running. For 1st pass, just open XCode for a Cocoa app, then IB



In conclusion ...

Objective-C is an object-oriented language, somewhat different from Java and C++

It has an extensive set of supporting classes (Frameworks)

Can be used to program Macintoshes

Can be used to program mobile devices (iPod Touch, iPod, iPad)

Tell this backwards: first describe then define





The end... of the beginning!


Objective-C - USALmaxus.fis.usal.es/HOTHOUSE/berlin/2010/hu2010objc.pdf · Stephen G. Kochan...

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