[Objective-C] message forwarding

IOS5 Developer's Cookbook에 나온 예제..

이 외에도 여러방법이 있다. 

	//
	// Car.h
	// Obj-C_Study
	//
	// Created by need4spd on 12. 12. 11..
	//
	//
	#import <Foundation/Foundation.h>
	@interface Car : NSObject
	{
	//int year;
	//NSString *make;
	//NSString *model;
	}
	@property (assign) int year;
	@property NSString *make;
	@property NSString *model;
	@property (readonly)NSString *carInfo;
	- (void) setMake:(NSString *) aMake andModel:(NSString *) aModel andYear:(int) aYear;
	- (void) printCarInfo;
	//- (int) year;
	@end

view raw car.h hosted with ❤ by GitHub

	//
	// Car.m
	// Obj-C_Study
	//
	// Created by need4spd on 12. 12. 11..
	//
	//
	#import "Car.h"
	@implementation Car
	@synthesize year, make, model, carInfo;
	- (id) init
	{
	self = [super init];
	if (!self) return nil;
	year = 1901;
	return self;
	}
	- (void) setMake:(NSString *)aMake andModel:(NSString *)aModel andYear:(int)aYear {
	make = aMake;
	model = aModel;
	year = aYear;
	}
	- (void) printCarInfo {
	if(!make) return;
	if(!model) return;
	printf("Car Info\n");
	printf("Make: %s\n", [make UTF8String]);
	printf("Model: %s\n", [model UTF8String]);
	printf("Year: %d\n", year);
	}
	- (NSString *) carInfo {
	return [NSString stringWithFormat:
	@"Car Info\n Make: %@\n Model: %@\n Yeary: %d", self.make ? self.make : @"Unknown", self.model ? self.model : @"Unknown Model", self.year];
	}
	- (NSMethodSignature *) methodSignatureForSelector:(SEL)aSelector {
	NSMethodSignature *signature = [super methodSignatureForSelector:@selector(UTF8String)];
	if(!signature) {
	signature = [[self carInfo] methodSignatureForSelector:@selector(UTF8String)];
	}
	return signature;
	}
	- (void) forwardInvocation:(NSInvocation *)anInvocation {
	NSLog(@"in invocation....");
	SEL selector = [anInvocation selector];
	if([carInfo respondsToSelector:selector]) {
	printf("[forwarding from %s to %s] ", [[[self class] description] UTF8String], [[NSString description] UTF8String]);
	[anInvocation invokeWithTarget:self.carInfo];
	}
	}
	@end

view raw car.m hosted with ❤ by GitHub

	//
	// RectangleTest.m
	// Obj-C_Study
	//
	// Created by on 12. 6. 22..
	// Copyright (c) 2012년 __MyCompanyName__. All rights reserved.
	//
	#import "Car.h"
	int main(int argc, char *argv[]) {
	@autoreleasepool {
	//Building And Access Array
	Car *car = [[Car alloc] init];
	NSLog(@"car info %@", [car carInfo]);
	[car setMake:@"make" andModel:@"model" andYear:1212];
	NSLog(@"signature %@ ", [signature description]);
	//forwarding
	printf("UTF8String: %s\n", [car performSelector:@selector(UTF8String)]);
	printf("length: %d\n", [car performSelector:@selector(length)]);
	//cannot compile code
	//printf("String length: %d\n", [car length]);
	}
	return 0;
	}

view raw test.m hosted with ❤ by GitHub

책에는 

signature = [[self carInfo] methodSignatureForSelector:@selector(UTF8String)];

이 부분이

signature = [carInfo methodSignatureForSelector:@selector(UTF8String)];

이렇게 되어있다. 이게 계속 null을 리턴해서, runtime error가 발생하는데 이유를 몰라서보니..

carInfo가 readonly이고, 값이 할당되지 않은 상태라서 null을 리턴하는 것 같아 [self carInfo]로 정상적으로 값이 할당된 NSString을 받아오도록 수정해보았다. 그랬더니 잘 되네... 

가장 간단한 forwarding은

forwardingTargetForSelector:(SEL)sel 쓰는거라고 되어있다..

암튼 null이 리턴되는 이유를 찾아내서 (확실하진 않지만..) 다행.. 아오 내 2시간....