This document provides an overview and introduction to building a basic fraction calculator app in Objective-C. It begins with an overview of the project architecture using the MVC pattern with a Fraction model class to represent fractions, a Calculator class to perform operations, and a ViewController class to manage the user interface. It then details the implementation of each class, including the Fraction class with methods for creating, modifying, and performing operations on fractions, the Calculator class for setting operands and performing operations, and the ViewController class for handling user interface events and updating the display.

1. Getting Started
Day 1

2. Where we’re headed:
‣Hello World
‣Xcode
‣About Objective-C
‣Syntax
‣Types
‣Operators
‣Classes & Objects Part 1
‣Fraction Calculator App

3. The Fraction Calculator
‣ Work with basic data
types
‣ Work with simple
objects and a simple
object model
‣ Basic MVC architecture
‣ Build a basic UI with
interface builder

4. Hello World

5. #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;
}
Hello World Example

6. Brief Xcode Tour

7. Starting a new project

8. The main window

9. The Console

10. Debug Window

11. Objective-C Basics

12. What is Objective-C
‣ An orthogonal superset over C
‣ Orthogonal = doesn’t override any C
functionality (almost)
‣ Object oriented
‣ Syntax a mix of SmallTalk and C
‣ Can be statically or dynamically typed

13. Objective-C Filetypes
‣ .xcodeproj - Your project bundle
‣ .h - header file
‣ .c - a C source file
‣ .m - an Objective-C source file
‣ .plist - a property list file

14. Syntax
‣ All statements end with a semi-colon
‣ Blocks (lower case ‘b’) are denoted by curly braces
‣ Comments:
‣ // in-line comment
‣ /* . . . . */ block comment
‣ # pre-processor directive

15. Syntax
Function Definition
int cube (int num)
{
return num * num;
}
Function Calls
cube (10);
Declaring Variables
int value = 10;

16. C Types
‣ Basic Types
‣ Int - an integer
‣ Float - decimal number
‣ Double - double precision decimal number
‣ Char - a single ASCII character (1 byte)
‣ Void - nothing (a variable cannot be declared void)
‣ Variations
‣ Signed / Unsigned (for ints)
‣ Long, long long (32 or 64 bits)
‣ Short (16 bits)
‣ Casting
‣ ( type ) variable

17. Objective-C Additions
‣ BOOL - boolean
‣ YES or NO
‣ id - pointer type for an objective-c object
‣ nil - the null value for objective-c

18. Esoteric Types
Struct
struct CGPoint {
CGFloat x;
CGFloat y;
};
Union
union aNumber {
int i;
float f;
}
Enum
enum CGRectEdge {
CGRectMinXEdge,
CGRectMinYEdge,
CGRectMaxXEdge,
CGRectMaxYEdge
};

19. Esoteric Types
Basic Typedef
typedef long NSInteger;
With a struct or enum
typedef struct {
CGFloat x;
CGFloat y;
} CGPoint;

20. Operators
‣ Arithmetic
‣ + addition
‣ - subtraction
‣ * multiplication
‣ / division
‣ % modulus
‣ Unary
‣ ++ increment
‣ -- decrement

21. Operators
‣ Assignment
‣ = simple assignment
‣ += add to
‣ -= subtract from
‣ *= multiply by
‣ /= divide by

22. Operators
‣ Logical
‣ == - equal to
‣ != - not equal to
‣ <, > - less than, greater than
‣ <=, >= - less than or equal, greater than or equal
‣ && - logical AND
‣ || - logical OR
‣ Pointers and References
‣ * - dereference
‣ & - reference (address of)

23. OO Syntax
‣ The ‘@’ symbol
‣ Used to create NSStrings
‣ Used as a prefix to obj-c keywords
‣ Calling Object Methods
[[NSAutoreleasePool alloc] init];
[NSDictionary dictionaryWithObject:@"foo" forKey:@"bar"];

24. Loops
For loop
for (int i = 0; i < 100; i++)
{
/* statements */
}
While loop
while (condition)
{
/* statements */
}
Do ... While loop
do {
/* statements */
} while (condition);

25. Branching
If ... else if ... else
if (condition)
{
/* statements */
}
else if (anotherCondition)
{
/* statements */
}
else
{
/* statements */
}

26. Branching
Switch
switch (expression)
{
case aConstant:
/* statements */
break;
case anotherConst:
/* statements */
break;
default:
/* statements */
break;
}
Ternary Operator
int value = condition ? 10 : 20;

27. Classes and Objects

28. What Defines an Object
‣Actions
‣Properties

29. A Car Object
‣ Properties
‣ Make
‣ Model
‣ Year
‣ Color
‣ Actions
‣ Accelerate
‣ Lock
‣ Steer

30. Objective-c Objects
‣ Data and Interface
Data Interface Message
‣Messages are sent to Objects
‣Objects may respond to messages

31. Messaging
‣ Messages are sent to objects
‣ Different than calling a method
‣ Messages are referred to as selectors
‣ The object knows its type and will respond
accordingly.
‣ All selectors are “virtual”
‣ Objects may respond to messages
‣ If the selector doesn’t exist (is unrecognized) an
exception is typically thrown.

32. Sample Class Interface
@interface MyClass : NSObject
{
int value
id someData
NSString *name
}
- (id)initWithName:(NSString *)name;
+ (MyClass *)createWithName:(NSString *)name;
@end

33. Sample Class Implementation
@implementation MyClass
- (id)initWithName:(NSString *)aname
{
self = [super init];
if (self)
{
name = [aname copy];
}
return self
}
+ (MyClass *)createWithName:(NSString *)name
{
return [[[self alloc] initWithName:name] autorelease];
}
@end

34. Named Properties
Named Property Declaration
@property (nonatomic, retain) NSString *name;
@property (nonatomic, assign) int value;
Interface Implementation
@synthesize name, value;
At compile time, the @synthesize produces getters
and setters.

35. Sample Class Interface
@interface MyClass : NSObject
{
int value
id someData
NSString *name
}
- (id)initWithName:(NSString *)name;
+ (MyClass *)createWithName:(NSString *)aname;
@property (nonatomic, retain) NSString *name;
@property (nonatomic, assign) int value;
@end

36. Sample Class Implementation
@implementation MyClass
@synthesize name, value;
- (id)initWithName:(NSString *)aname
{
self = [super init];
if (self)
{
name = [aname copy];
}
return self
}
+ (MyClass *)createWithName:(NSString *)name
{
return [[[self alloc] initWithName:name] autorelease];
}

37. Fraction Calculator

38. Project Overview
‣ Fraction Class
‣ Calculator Class
‣ View Controller
‣ UI File (.xib)

39. Architecture
View
Xib file Calculator
Controller
Fraction
View Controller “Model”

40. The Fraction Class
‣ Properties
‣ Numerator
‣ Denominator
‣ Actions
‣ Create
‣ Set properties
‣ Add, Subtract fractions
‣ Multiply, Divide fractions
‣ Reduce

41. Fraction Interface
@interface Fraction : NSObject
{
int numerator;
int denominator;
}
- (id)initWithNumerator:(int)num denominator:(int)denom;
- (double)asDecimal;
- (Fraction *)add:(Fraction *)fraction;
- (Fraction *)subtract:(Fraction *)fraction;
- (Fraction *)multiply:(Fraction *)fraction;
- (Fraction *)divide:(Fraction *)fraction;
- (void)reduce;
@property (nonatomic, assign) int numerator;
@property (nonatomic, assign) int denominator;
@end

42. Fraction Implementation
#import "Fraction.h"
@implementation Fraction
@synthesize numerator;
@synthesize denominator;

43. Fraction Implementation
- (id)initWithNumerator:(int)num denominator:(int)denom
{
if (self = [super init])
{
numerator = num;
denominator = denom != 0 ? denom : 1;
}
return self;
}
- (NSString *)description
{
return [NSString stringWithFormat:@"Fraction: %d/%d", numerator,
denominator];
}

44. Fraction Implementation
- (void)setDenominator:(int)denom
{
if (denom != 0)
{
denominator = denom;
}
else
{
denominator = 1;
}
}
- (double)asDecimal
{
return (double)numerator / denominator;
}

45. Fraction Implementation
// page 144
- (Fraction *)add:(Fraction *)fraction
{
int resultNum, resultDenom;
resultNum = numerator * fraction.denominator
+ denominator * fraction.numerator;
resultDenom = denominator * fraction.denominator;
Fraction *result = [[Fraction alloc] initWithNumerator:resultNum
denominator:resultDenom];
[result reduce];
return result;
}

46. Fraction Implementation
- (Fraction *)subtract:(Fraction *)fraction
{
Fraction *tmp = [[Fraction alloc] initWithNumerator:
-fraction.numerator
denominator:fraction.denominator];
Fraction *result = [self add:tmp];
[tmp release];
return result;
}

47. Fraction Implementation
- (Fraction *)multiply:(Fraction *)fraction
{
int resultNum, resultDenom;
resultNum = numerator * fraction.numerator;
resultDenom = denominator * fraction.denominator;
Fraction *result = [[Fraction alloc] initWithNumerator:resultNum
denominator:resultDenom];
[result reduce];
return result;
}

48. Fraction Implementation
- (Fraction *)divide:(Fraction *)fraction
{
Fraction *tmp = [[Fraction alloc] initWithNumerator:fraction.denominator
denominator:fraction.numerator];
Fraction *result = [self multiply:tmp];
[tmp release];
return result;
}

49. Fraction Implementation
// page 146
- (void)reduce
{
int tmpNum = numerator;
int tmpDen = denominator;
int temp = 0;
while (tmpDen != 0)
{
temp = tmpNum % tmpDen;
tmpNum = tmpDen;
tmpDen = temp;
}
numerator /= tmpNum;
denominator /= tmpNum;
}

50. Calculator Class
‣ Properties
‣ An operation to perform
‣ 2 operands
‣ A result of an operation
‣ Actions
‣ Set properties
‣ Perform an operation

51. Calculator Interface
#import "Fraction.h"
typedef enum
{
CalcOpAdd,
CalcOpMul,
CalcOpDiv,
CalcOpSub
} CalculatorOperation;
@interface Calculator : NSObject
{
Fraction *operand1;
Fraction *operand2;
Fraction *result;
}
- (void)performOperation:(CalculatorOperation)op;
- (void)reset;
@property (nonatomic, retain) Fraction *operand1, *operand2;
@property (nonatomic, readonly) Fraction *result;
@end

52. Calculator Implementation
#import "Calculator.h"
@implementation Calculator
@synthesize operand1, operand2, result;
- (void)dealloc
{
[operand1 release];
[operand2 release];
[result release];
[super dealloc];
}

53. Calculator Implementation
- (void)performOperation:(CalculatorOperation)op
{
switch (op) {
case CalcOpAdd:
result = [operand1 add:operand2];
break;
case CalcOpSub:
result = [operand1 subtract:operand2];
break;
case CalcOpMul:
result = [operand1 multiply:operand2];
break;
case CalcOpDiv:
result = [operand1 divide:operand2];
break;
default:
break;
}
}

54. Calculator Implementation
- (void)reset
{
self.operand1 = nil;
self.operand2 = nil;
[result release];
result = nil;
}
@end

55. View Controller
‣ Subclass of UIViewController
‣ Properties
‣ View
‣ Actions
‣ Respond to UI Events
‣ Manipulate UI Elements
‣ As a subclass of UIViewController, many functions
are provided already.

56. VC Interface
@interface FractionCalculatorViewController : UIViewController
{
UILabel *display;
NSMutableString *displayString;
Calculator *calculator;
CalculatorOperation op;
BOOL workingNumerator;
BOOL workingFirstNumber;
}

57. VC Interface
- (IBAction)numberButtonTap:(UIButton *)sender;
- (IBAction)opButtonTap:(UIButton *)sender;
- (IBAction)overButtonTap:(UIButton *)sender;
- (IBAction)clearButtonTap:(UIButton *)sender;
- (IBAction)equalsButtonTap:(UIButton *)sender;
@property (nonatomic, retain) IBOutlet UILabel *display;
@property (nonatomic, retain) NSMutableString *displayString;

58. VC Interface
typedef enum {
OperatorButtonTagAdd = 10,
OperatorButtonTagSub = 11,
OperatorButtonTagMul = 12,
OperatorButtonTagDiv = 13
} OperatorButtonTag;

59. VC Implementation
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
if ((self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]))
{
calculator = [[Calculator alloc] init];
displayString = [[NSMutableString alloc] init];
workingNumerator = YES;
workingFirstNumber = YES;
}
return self;
}
- (void)dealloc
{
[display release];
[displayString release];
[calculator release];
[super dealloc];
}

60. VC Implementation
- (IBAction)numberButtonTap:(UIButton *)sender
{
[displayString appendString:[NSString stringWithFormat:@"%d", [sender tag]]];
Fraction *f;
if (workingFirstNumber)
{
if (calculator.operand1 == nil)
{
calculator.operand1 = [[Fraction alloc] init];
}
f = calculator.operand1;
}
else
{
if (calculator.operand2 == nil)
{
calculator.operand2 = [[Fraction alloc] init];
}
f = calculator.operand2;
}

61. VC Implementation
if (workingNumerator)
{
f.numerator *= 10;
f.numerator += [sender tag];
}
else
{
f.denominator *= 10;
f.denominator += [sender tag];
}
[display setText:displayString];
}

62. VC Implementation
- (IBAction)opButtonTap:(UIButton *)sender
{
switch ([sender tag])
{
case OperatorButtonTagAdd:
op = CalcOpAdd;
[displayString appendString:[NSString stringWithFormat:@" + "]];
break;
case OperatorButtonTagSub:
op = CalcOpSub;
[displayString appendString:[NSString stringWithFormat:@" - "]];
break;
case OperatorButtonTagMul:
op = CalcOpMul;
[displayString appendString:[NSString stringWithFormat:@" x "]];
break;
case OperatorButtonTagDiv:
op = CalcOpDiv;
[displayString appendString:[NSString stringWithFormat:@" ÷ "]];
break;
default:
break;
}
workingFirstNumber = NO;
workingNumerator = YES;
[display setText:displayString];
}

63. VC Implementation
- (IBAction)clearButtonTap:(UIButton *)sender
{
workingFirstNumber = YES;
workingNumerator = YES;
calculator.operand1 = nil;
calculator.operand2 = nil;
[displayString setString:@""];
[display setText:displayString];
}
- (IBAction)overButtonTap:(UIButton *)sender
{
[displayString appendString:@" / "];
[display setText:displayString];
workingNumerator = NO;
}

64. VC Implementation
- (IBAction)equalsButtonTap:(UIButton *)sender
{
NSLog(@"%@ %@", calculator.operand1, calculator.operand2);
[calculator performOperation:op];
[displayString setString:[NSString stringWithFormat:@"%d / %d", calculator.result.numerator,
calculator.result.denominator]];
[display setText:displayString];
}
- (void)dealloc
{
[display release];
[displayString release];
[calculator release];
[super dealloc];
}

65. UIApplication Delegate
‣ Handles application after initial load.
‣ Houses the view controller

66. Application Delegate
- (BOOL)application:(UIApplication *)application
didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
// Override point for customization after application launch.
mainViewController = [[FractionCalculatorViewController alloc]
initWithNibName:@"FractionCalculatorViewController"
bundle:nil];
[window addSubview:mainViewController.view];
[window makeKeyAndVisible];
return YES;
}

67. Creating the fraction UI

68. UI Files are xib files

69. Object Properties Object Library