[Objective C] 08 Categories

프로그래밍/iPhone Dev 2009. 11. 9. 17:25 Posted by galad
Categories

Fraction.h
#import <Foundation/NSObject.h>

@interface Fraction: NSObject {
    int numerator;
    int denominator;
}

-(Fraction*) initWithNumerator: (int) n andDenominator: (int) d;
-(Fraction*) initWithNumerator: (int) n denominator: (int) d;
-(void) print;
-(void) setNumerator: (int) n;
-(void) setNumerator: (int) n andDenominator: (int) d;
-(void) setDenominator: (int) d;
-(int) numerator;
-(int) denominator;
@end

Fraction.m
#import "Fraction.h"
#import <stdio.h>

@implementation Fraction
-(Fraction*) initWithNumerator: (int) n andDenominator: (int) d {
    self = [super init];
   
    if(self) {
        [self setNumerator: n andDenominator: d];
    }
   
    return self;
}

-(Fraction*) initWithNumerator: (int) n denominator: (int) d {
    self = [super init];
   
    if(self) {
        [self setNumerator: n andDenominator: d];
    }
   
    return self;
}

-(void) print {
    printf( "%i/%i", numerator, denominator );
}

-(void) setNumerator: (int) n {
    numerator = n;
}

-(void) setNumerator: (int) n andDenominator: (int) d {
    numerator = n;
    denominator = d;
}

-(void) setDenominator: (int) d {
    denominator = d;
}

-(int) denominator {
    return denominator;
}

-(int) numerator {
    return numerator;
}
@end

FractionMath.h
#import "Fraction.h"

@interface Fraction (Math)
-(Fraction*) add: (Fraction*) f;
-(Fraction*) mul: (Fraction*) f;
-(Fraction*) div: (Fraction*) f;
-(Fraction*) sub: (Fraction*) f;
@end

FractionMath.m
#import "FractionMath.h"

@implementation Fraction (Math)
-(Fraction*) add: (Fraction*) f {
    return [[Fraction alloc] initWithNumerator: numerator * [f denominator] +
                                                denominator * [f numerator]
                             denominator: denominator * [f denominator]];
}

-(Fraction*) mul: (Fraction*) f {
    return [[Fraction alloc] initWithNumerator: numerator * [f numerator]
                             denominator: denominator * [f denominator]];

}

-(Fraction*) div: (Fraction*) f {
    return [[Fraction alloc] initWithNumerator: numerator * [f denominator]
                             denominator: denominator * [f numerator]];
}

-(Fraction*) sub: (Fraction*) f {
    return [[Fraction alloc] initWithNumerator: numerator * [f denominator] -
                                                denominator * [f numerator]
                             denominator: denominator * [f denominator]];
}
@end

main.m
#import <stdio.h>
#import "Fraction.h"
#import "FractionMath.h"

int main( int argc, const char *argv[] ) {
    // create a new instance
    Fraction *frac1 = [[Fraction alloc] initWithNumerator: 1 denominator: 3];
    Fraction *frac2 = [[Fraction alloc] initWithNumerator: 2 denominator: 5];
    Fraction *frac3 = [frac1 mul: frac2];

    // print it
    [frac1 print];
    printf( " * " );
    [frac2 print];
    printf( " = " );
    [frac3 print];
    printf( "\n" );

    // free memory
    [frac1 release];
    [frac2 release];
    [frac3 release];

    system("PAUSE");
    return 0;
}

결과
1/3 * 2/5 = 2/15
계속하려면 아무 키나 누르십시오 . . .

- There can only be one category with the same name. Additional cateogies may be added on with different but unqiue names.
- 카테고리는 인스턴스 변수를 가질 수 없음.
- Categories are useful for creating private methods. Obejctive-C에는 java의 private/protected/public 같은 개념이 없어서 카테고리로 그런 기능을 할 수 있다. 단 class의 private 메소드를 .m 파일에 옮겨놓을 것. 다음이 좋은 예.

MyClass.h
#import <Foundation/NSObject.h>

@interface MyClass: NSObject
-(void) publicMethod;
@end

MyClass.m
#import "MyClass.h"
#import <stdio.h>

@implementation MyClass
-(void) publicMethod {
    printf( "public method\n" );
}
@end

// private methods
@interface MyClass (Private)
-(void) privateMethod;
@end

@implementation MyClass (Private)
-(void) privateMethod {
    printf( "private method\n" );
}
@end

main.m
#import "MyClass.h"

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

    // this compiles
    [obj publicMethod];

    // this throws errors when compiling
    //[obj privateMethod];

    // free memory
    [obj release];
   
    return 0;
}

- private 메소드로 쓰는 건 좋으나 그 외에는 솔직히 어디다 써야할 지 감이 안 옴...
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[Objective C] 05 The Id Type  (1) 2009.10.29
 

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