[Objective C] 10 Protocols

Protocols
자바의 인터페이스, C++의 버츄얼 클래스 같은 것
상속 받은 클래스에게 이것은 꼭 구현해야 한다고 규정 짓는 것. 말 그대로 프로토콜.

Printing.h

// 프로토콜 정의 @protocol Printing -(void) print; @end

Fraction.h

#import <Foundation/NSObject.h> #import "Printing.h" // <> 안이 프로토콜. // NSObejct를 상속하고, Printing과 NSCopying을 프로토콜로 구현 @interface Fraction: NSObject <Printing, NSCopying> {     int numerator;     int denominator; } -(Fraction*) initWithNumerator: (int) n denominator: (int) d; -(void) setNumerator: (int) d; -(void) setDenominator: (int) d; -(void) setNumerator: (int) n andDenominator: (int) d; -(int) numerator; -(int) denominator; @end

Fraction.m

#import "Fraction.h" #import <stdio.h> @implementation Fraction -(Fraction*) initWithNumerator: (int) n denominator: (int) d {     self = [super init];     if ( self ) {         [self setNumerator: n andDenominator: d];     }     return self; } // Fraction.h에는 정의 되어 있지 않으나, 프로토콜 Printing에 정의되어 있는 것을 구현 -(void) print {     printf( "%i/%i", numerator, denominator ); } -(void) setNumerator: (int) n {     numerator = n; } -(void) setDenominator: (int) d {     denominator = d; } -(void) setNumerator: (int) n andDenominator: (int) d {     numerator = n;     denominator = d; } -(int) denominator {     return denominator; } -(int) numerator {     return numerator; } // print method와 마찬가지로 NSCopying 프로토콜을 구현 -(Fraction*) copyWithZone: (NSZone*) zone {     return [[Fraction allocWithZone: zone] initWithNumerator: numerator                                            denominator: denominator]; } @end

Complex.h

#import <Foundation/NSObject.h> #import "Printing.h" @interface Complex: NSObject <Printing> {     double real;     double imaginary; } -(Complex*) initWithReal: (double) r andImaginary: (double) i; -(void) setReal: (double) r; -(void) setImaginary: (double) i; -(void) setReal: (double) r andImaginary: (double) i; -(double) real; -(double) imaginary; @end

Complex.m

#import "Complex.h" #import <stdio.h> @implementation Complex -(Complex*) initWithReal: (double) r andImaginary: (double) i {     self = [super init];     if ( self ) {         [self setReal: r andImaginary: i];     }     return self; } -(void) setReal: (double) r {     real = r; } -(void) setImaginary: (double) i {     imaginary = i; } -(void) setReal: (double) r andImaginary: (double) i {     real = r;     imaginary = i; } -(double) real {     return real; } -(double) imaginary {     return imaginary; } -(void) print { //    printf( "%_f + %_fi", real, imaginary );     printf( "%f + %f", real, imaginary ); } @end

main.m

#import <stdio.h> #import "Fraction.h" #import "Complex.h" int main( int argc, const char *argv[] ) {     // create a new instance     Fraction *frac = [[Fraction alloc] initWithNumerator: 3 denominator: 10];     Complex *comp = [[Complex alloc] initWithReal: 5 andImaginary: 15];     id <Printing> printable;     id <NSCopying, Printing> copyPrintable;     // print it     printable = frac;     printf( "The fraction is: " );     [printable print];     printf( "\n" );     // print complex     printable = comp;     printf( "The complex number is: " );     [printable print];     printf( "\n" );     // this compiles because Fraction comforms to both Printing and NSCopyable     copyPrintable = frac;     // this doesn't compile because Complex only conforms to Printing     //copyPrintable = comp;     // test conformance     // true     if ( [frac conformsToProtocol: @protocol( NSCopying )] == YES ) {         printf( "Fraction conforms to NSCopying\n" );     }     else {         printf( "Fraction doesn't conform to NSCopying\n" );     }     // false     if ( [comp conformsToProtocol: @protocol( NSCopying )] == YES ) {         printf( "Complex conforms to NSCopying\n" );     }     else {         printf( "Complex doesn't conform to NSCopying\n" );     }         // test id type     id f; // 그냥 id 타입으로 받아도 상관없음. 다만 엄격한 사용을 위해 위와 같이 protocol을 지정.         f = frac;     [f print];     printf( "\n" );         f = comp;     [f print];     printf( "\n" );     // free memory     [frac release];     [comp release];     system("PAUSE");     return 0; }

결과

The fraction is: 3/10 The complex number is: 5.000000 + 15.000000 Fraction conforms to NSCopying Complex doesn't conform to NSCopying 3/10 5.000000 + 15.000000 계속하려면 아무 키나 누르십시오 . . .

- The methods that the protocol requires to be implemented are not required to be in the list of methods for the header file. As you can see, Complex.h doesn't have a definition for -(void) print, but it still implements it since it conforms to the protocol.
- One unique aspect of Objective-C's interface system is how you specify types. Rather than specifying it like Java or C++ as: Printing *someVar = ( Printing * ) frac; for example, you use the id type with a restricted protocol: id <Printing> var = frac; This allows you to dynamically specify a type that requires multiple protocols, all with one variable. Such as: id <Printing, NSCopying> var = frac;
- Much like using @selector for testing an object's inheritance, you can use @protocol to test for conformance of interfaces. [object conformsToProtocol: @protocol( SomeProtocol )] returns a BOOL if the object conforms to that protocol. This works the same for classes as well: [SomeClass conformsToProtocol: @protocol( SomeProtocol )].