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Introduction to Objective-Cand

iPhone Development

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Introduction

• Objective-C is implemented as set of extensions to the C language.

• It's designed to give C a full capability for object-oriented programming, and to do so in a simple and straightforward way.

• Its additions to C are few and are mostly based on Smalltalk, one of the first object-oriented programming languages.

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Why Objective C

• Objective-C incorporates C, you get all the benefits of C when working within Objective-C.

• You can choose when to do something in an object-oriented way (define a new class, for example) and when to stick to procedural programming techniques (define a struct and some functions instead of a class).

• Objective-C is a simple language. Its syntax is small, unambiguous, and easy to learn

• Objective-C is the most dynamic of the object-oriented languages based on C. Most decisions are made at run time.

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Object-Oriented Programming

• The insight of object-oriented programming is to combine state and behavior, data and operations on data, in a high-level unit, an object, and to give it language support.

• An object is a group of related functions and a data structure that serves those functions. The functions are known as the object's methods, and the fields of its data structure are its instance variables.

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The Objective-C Language

• The Objective-C language is fully compatible with ANSI standard C

• Objective-C can also be used as an extension to C++.

• Although C++ itself is a Object-Oriented Language, there are difference in the dynamic binding from Objective-C

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Objective-C Language (cont.)

• Objective-C source files have a “.m” extension

• “.h” file is the interface file

• For example:– main.m – List.h (Interface of List class.) – List.m (Implementation of List class.)

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ID

• “id” is a data type used by Objective-C to define a pointer of an object (a pointer to the object’s data)

• Any type of object, as long as it is an object, we can use the id data type.

• For example, we can define an object by:

id anObject;• nil is the reserved word for null object

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Dynamic Typing

• “id” data type has no information about the object

• Every object carries with it an isa instance variable that identifies the object's class, that is, what kind of object it is.

• Objects are thus dynamically typed at run time. Whenever it needs to, the run-time system can find the exact class that an object belongs to, just by asking the object

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Messages

• To get an object to do something, you send it a message telling it to apply a method. In Objective-C, message expressions are enclosed in square brackets

[receiver message]

• The receiver is an object. The message is simply the name of a method and any arguments that are passed to it

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Messages (cont.)

• For example, this message tells the myRect object to perform its display method, which causes the rectangle to display itself

[myRect display];

[myRect setOrigin:30.0 :50.0]; • The method setOrigin::, has two colons, one for

each of its arguments. The arguments are inserted after the colons, breaking the name apart

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Polymorphism

• Each object has define its own method but for different class, they can have the same method name which has totally different meaning

• The two different object can respond differently to the same message

• Together with dynamic binding, it permits you to write code that might apply to any number of different kinds of objects, without having to choose at the time you write the code what kinds of objects they might be

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Inheritance

• Root class is NSObject• Inheritance is cumulative.

A Square object has the methods and instance variables defined for Rectangle, Shape, Graphic, and NSObject, as well as those defined specifically for Square

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Inheritance (cont.)

• Instance Variables: The new object contains not only the instance variables that were defined for its class, but also the instance variables defined for its super class, all the way back to the root class

• Methods: An object has access not only to the methods that were defined for its class, but also to methods defined for its super class

• Method Overriding: Implement a new method with the same name as one defined in a class farther up the hierarchy. The new method overrides the original; instances of the new class will perform it rather than the original

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Class Objects

• Compiler creates one class object to contain the information for the name of class and super class

• To start an object in a class:id myRectx; myRect = [[Rectangle alloc] init];

• The alloc method returns a new instance and that instance performs an init method to set its initial state.

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Defining a Class

• In Objective-C, classes are defined in two parts: – An interface that declares the methods and

instance variables of the class and names its super class

– An implementation that actually defines the class (contains the code that implements its methods)

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The Interface

• The declaration of a class interface begins with the compiler directive @interface and ends with the directive @end

@interface ClassName : ItsSuperclass { instance variable declarations

} method declarations

@end

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Declaration

• Instance Variablesfloat width;float height; BOOL filled; NSColor *fillColor;

• Methods:• names of methods that can be used by class

objects, class methods, are preceded by a plus sign+ alloc

• methods that instances of a class can use, instance methods, are marked with a minus sign: - (void) display;

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Declaration (cont.)

• Importing the Interface: The interface is usually included with the #import directive

#import "Rectangle.h"

• To reflect the fact that a class definition builds on the definitions of inherited classes, an interface file begins by importing the interface for its super class

• Referring to Other Classes: If the interface mentions classes not in this hierarchy, it must declare them with the @class directive:

@class Rectangle, Circle;

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The Implementation#import "ClassName.h" @implementation ClassName

method definitions @end

- makeIdenticalTwin {

if ( !twin ) { twin = [[Sibling alloc] init]; twin->gender = gender; twin->appearance = appearance; } return twin;

}

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Implementation (cont.)

Example:@interface Worker : NSObject {

char *name; @private

int age; char *evaluation;

@protected id job; float wage;

@public id boss;

}

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Implementation (cont.)

- promoteTo:newPosition

{

id old = job;

job = newPosition;

return old;

}

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GCC and Objective-C

• Objective-C is layered on top of the C language• iPhone & iPad “native” applications are written in

Objective C• The Apple dev kit for Objective-C is called

“Cocoa”• Can be written on any computer that has GCC

plus “GNUstep” plug-in• Apple computers have all of this pre-installed,

and also have an iPhone simulator in the XCode IDE

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Tools

• Apple: pre-installed with the Cocoa frameworks– XCode or GCC in terminal window

• Ubuntu: GnuStep is a free clone of Cocoa– sudo aptget

– install buildessentials

– gobjc gnustep

– gnustepmake

– gnustepcommon

– libgnustepbasedev

• Windows: http://www.gnustep.org/

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File Overview

• Source code files have a .m extension

• Header files have a .h extension

• You can use gcc to compile in the same way as C code

• But, you will need to add the Cacoa or GNUStep frameworks to the build.

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Example: Hello World#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) {     NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    // insert code here...     NSLog(@"Hello, World!");     [pool drain];     return 0; }

NSLog() is equivalent to a C printf()Very similar to CC programs are valid in Objective-C

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Compiling Hello World in Xcode(Mac)

• File->New Project– Mac OS X category – Select Application– Command Line Tool– Type - “Foundation”

• Name project helloworld and choose folder• Edit helloworld.m and paste in our example over the top of

the default. The default code is this sample program.• Save.• Note that Foundation.framework has been included for us

already• “Build and run”.• The debugger console should show “Hello World”

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Compiling Hello World on Terminal(Mac)

• Write hello.m using a plain text editor• To comple type:

gcc – framework Foundation hello.m –o hello

• Foundation brings in the Foundation framework (Cocoa) which

• bundles together a set of dependencies (header files and libraries). You will need this every time we compile Objective C code.

• Type: ./hello will run the program in the terminal• Note: this approach is fine for early examples but

the iPhone applications will be much easier to build in XCode.

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Intro to HelloWorld

• Objective-C uses a string class similar to the std::string or Java string. It is called NSString.

• Constant NSStrings are preceded by @ for example: @”Hello World”

• You will notice that NSLog() also outputs time and date and various extra information.

• NSAutoreleasePool* pool =[[NSAutoreleasePool• alloc] init]; allocates a lump of memory• Memory must be freed with [pool drain];

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Example 2#import <Foundation/Foundation.h>

int main(int argc, const char* argv[]) { NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];

NSLog (@”Hello World”);

int undergrads = 120; int postgrads = 50; int students = undergrads + postgrads;

NSLog (@”Now featuring...\n %i Computer Science students”, students);

[pool drain];

return 0;}

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Some things to note

• No line break needed at end of NSLog statements.

• NSString constants use C-style variables.

• Test this program to see results.

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@interface

@interface ClassName : ParentClassName{declare member variable here;declare another member variable here;}declare method functions here;@end

• Equivalent to C class declaration• Goes in header (.h) file• Functions outside curly braces• Don’t forget the @end tag

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@implementation

#import <Foundation/Foundation.h>#include "ComputerScience.h“

@implementation ClassNamedefine method function here;define another method function here;define yet another method function here;@end

● Equivalent to C class function definitions● Goes in source (.m) file● Don't forget the @end tag

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Example 3: ComputerScience.h

@interface ComputerScience : NSObject{ int mUndergrads; int mPostgrads;}-(void) print;-(void) setUndergrads: (int) undergrads;-(void) setPostgrads: (int) postgrads;@end

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Some things to note

• NSObject is the “root” object in Objective-C• No direct access to instance variables so we write

some get/set “instance methods”• Instance methods (affect internal state of class)

are preceded with a minus sign• “Class methods” (higher level functions) are

preceded with a plus sign e.g. create new class• Method return type in parentheses• Semicolon before list of parameters• Parameter type in parenthesis, followed by name

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Example 3: ComputerScience.m#include “ComputerScience.h”

@implementation ComputerScience-(void) print {

int totalStudents = mUndergrads + mPostgrads;

NSLog (@”Total students in CompSci = %i”, totalStudents);

}

-(void) setUndergrads: (int) undergrads { mUndergrads = undergrads;}-(void) setPostgrads: (int) postgrads { mPostgrads = postgrads;}@end

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Some things to note

• Note prefix minus sign

• Very similar to C

• Same format as with the interface

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Example2: main.m#import <Foundation/Foundation.h>#include “ComputerScience.h”

int main(int argc, char* argv[]) {NSAutoreleasePool* pool = [[NSAutoreleasePool alloc]

init];ComputerScience* ituCompSci; // pointerituCompSci = [ComputerScience alloc]; // allocate memoryituCompSci = [ituCompSci init]; // initialize[ituCompSci setUndergrads: 120]; // apply method to

instance[ituCompSci setPostgrads: 2000];[ituCompSci print];[ituCompSci release];[pool drain];return 0;}

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Some things to note

• Applying methods to instance format: [receiver message];

• Semi-colon for variables or values passed to methods

• [pool drain] etc. are also applying methods.

• Built-in messages; alloc, init, release.

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Some other things to note

• alloc is equivalent to C++ new but it also zeros all variables

• init should be applied to an instance before use

• These are often combined in shorthand: ComputerScience* ituCompSci = [[ComputerScience alloc] init];

• There is no garbage collection on the iPhone, so we should release all of our instance memory.

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To compile example 3

• Create a project in Xcode

• Delete the original main.m

• Add existing files to the project

• Compile and run!

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Data Structures• Objective-C arrays are similar to C arrays, but

you can initialize whole array in a list.• Or just a few indices of the array. The rest are

set to 0.• Or mix and match; the example will create an

array of size [8].int values[3] = { 3, 4, 2 };char letters[3] = { 'a', 'c', 'x' };float grades[100] = {10.0,11.2,1.1};int array[] = {[3]=11,[2]=1,[7]=0};

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Multi-dimensional Arrays

• Can be initialized by using subset notation with braces. Note no comma after second subset.

• Subset braces are optional, the compiler will fill in blanks where it can as with 1D arrays.

int array[2][3] = {

{ 0, 3, 4},

{ 1, 1, 1}

};

int array[2][3] = {0, 3, 4, 1, 1, 1};

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Arrays and Functions• Arrays can be passed as arguments to functions.• This function will print every integer in an array but it needs

to also be told how long the array is (arrayLength).• Statements with hard-coded indices such as array[4] are

potentially dangerous.

void function(int array[], int arrayLength) { int fourthValue = array[4]; for (int i = 0; i < arrayLength; i++) { NSLog(@”%i”, array[i]; }}

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Structs

• Similarly the Objective C “struct” can be

• initialized in one go.

• Use the '.' member notation or just use values in the correct order or use some values. 'unknown.'

• In the following example we explicitly define the last member, but the others are undefined.

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Structsstruct ComputerScience { int BSYears; int PhDYears; int WellSpentYears;};

struct ComputerScience myCareer = { .BSYears = 3, .PhDYears = 3, .WellSpentYears = 6};

struct ComputerScience poorLifeDecisions = { 3, 8, 3 };struct ComputerScience unknown = { 3 };struct ComputerScience andFurtherMore = { .WellSpentYears

= 0 };

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Declare+Define a Struct in One

• Similar to the older C-style notation.

• The example will declare a coffee order struct and immediately define an instance called “complexityGroup”.

struct coffeeOrder {

int Plain;

int DoubleEspresso;

} complexityGroup = { 7, 4 };

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Fitting into limited memory: Bit fields

• To work on devices with memory limitations we can manually define the bit size of variables.

• Using a struct, all of the members are packed together efficiently.

• The next example divides a 16-bit unsigned integer into 3 on/off bit flags, a 10-bit number and a 3-bit number.

• Note that it is valid to use Boolean operations on single bit variables.

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Fitting into limited memory: Bit fields

struct AlarmPanelStruct {unsigned int DoorAlarmTriggered:1;unsigned int WindowAlarmTriggered:1;unsigned int TrapdoorAlarmTriggered:1;unsigned int AdministratorsID:10;unsigned int AlarmKeyCode:3;};struct AlarmPanelStruct lab;lab.AlarmCode = 1;lab.DoorAlarmTriggered = 0;if (DoorAlarmTriggered) ...

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Fitting into limited memory: Unions

• Union data structures allow ambiguity.• Useful for allowing one storage area to hold different

variable types.• Can only hold one of the variables at a time.• Must be careful to ensure retrieval type matches last type

stored.• Might come in handy for storing lists of “data” that might be

of different types.• The next example gives ones potentially practical use;• A series of recordings store ‘Data.’• The struct has a char to indicate the type of data recorded

in Data.

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Fitting into limited memory: Unionsunion OneOfTheFollowing { char Letter; int CountOf; float Average;};

OneOfTheFollowing lastSpaceOnThePhone;lastSpaceOnThePhone.Letter = 'a';lastSpaceOnThePhone.CountOf = 1;

struct RecordedData {char* Name;union { float RealNumber; int Integer; char Letter;} Data; // immediately defines an instancechar TypeOfData;} arrayOfRecordedData[100];

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Simulated iOS Apps

• Relies heavily on the XCode IDE.• iPhone and iPad Simulator program is a free add-on for Xcode. You

just need a Mac computer to develop an iOS app.• Running or testing apps on an actual device is not free (~100

USD/year).• The process of deploying an app to a device is quite involved.

1. Software set-up2. Developer sign-up3. Member sign-up4. Certificate request

• Software comes as one bundle• Latest Xcode plus Simulators• Apple Organizer• GUI designer

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Something to note!

• You can program for either the iPhone or the iPad or both in the latest XCode.

• If you are going to do the examples for both simultaneously be aware that there are two sets of .h and .m files (one for each).

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Frameworks

• UIKit.framework for developing standard iOS GUIs (buttons etc.)

• UITextField (user-entered text that brings up the keyboard)

• UIFont• UIView• UITableView• UIImageView• UIImage• UIButton (a click-able button)• UILabel (a string of text on-screen)• UIWindow (main Window on iPhone)

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iOS programming

• Event driven framework• Interface Designer has some extra macros for

the code that act like hooks to variables;– IBAction - trigger events like mouse clicks– IBOutlet - captures outputs from events

• These tags are not compiled (don't affect the code) but sit as an extra before variables that the Interface Designer can see.

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Start a New XCode iOS Project

• New Project → iPhone/iPad OS• Navigation-Based - “navigation controller” as

used in Contacts app.• OpenGL ES - cut-down OpenGL• Tab Bar – app in style of iPod app.• Utility – Flipside app in style of stock quote app.• View-Based – single view that you draw into and

display to screen.• Window-Based – basic app with a main

window. (we will use this one for examples.)

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Try Out - Hello World

• Watch the Hello World tutorial and build your first iPhone application.

• The tutorial can be found at:

http://www.youtube.com/watch?v=lR-t5vEpueQ

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End of Lecture 1

• Next time, we will be doing more Object-C programming and building more iPhone applications.

• Make sure to practice with the “Hello World” application before next week so you can move forward with more complex concepts and programming methods.