OC-消息转发多继承

#import "ViewController.h"
#import "Programmer.h"
#import "Singer.h"
#import "Artist.h"

@interface ViewController ()

@end

@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];

    Programmer * grammer = [Programmer new];
    // 在performSelector中使用NSSelectorFromString会造成警告
    // 可以通过设置不检测performSelector内存泄露关闭警告
    //[grammer performSelector:NSSelectorFromString(@"sing") withObject:nil];
    //或者通过类型强转来实现，无警告
    [(Artist*)grammer draw];
    [(Singer*)grammer sing];
}
@end

#import <Foundation/Foundation.h>

@interface Programmer : NSObject

@end

#import "Programmer.h"
#import "Singer.h"
#import "Artist.h"

@implementation Programmer
// 通过消息转发实现多继承
- (id)forwardingTargetForSelector:(SEL)aSelector {
    Singer * singer = [[Singer alloc] init];
    Artist * artist = [[Artist alloc] init];
    
    if ([singer respondsToSelector:aSelector]) {
        return singer;
    }
    else if ([artist respondsToSelector:aSelector]) {
        return artist;
    }
    return nil;
}
@end

#import <Foundation/Foundation.h>

@interface Artist : NSObject
// 画家可以绘画
- (void)draw;
@end

#import "Artist.h"

@implementation Artist
-(void)draw {
   NSLog(@"I can draw");
}
@end

#import <Foundation/Foundation.h>

@interface Singer : NSObject
// 歌手会唱歌
- (void)sing;
@end

#import "Singer.h"

@implementation Singer
- (void)sing {
    NSLog(@"I can sing");
}
@end