OC Protocol----协议

@protocol Client <NSObject>  
-(void)defaultMethod;//默认必须实现  
  
@required//必须  
-(void)required；  
  
@optional//可选  
-(void)optional;  
@end  

 

#import "Client.h"  
@interface JackClient : NSObject<Client>  
  
@end   
  
@implementation JackClient  
-(void)defaultMethod{  
    NSLog(@"this is defaultMethod");  
}  
  
-(void)required{  
    NSLog(@"this is required method");  
}  
@end  

#import "Client.h"  
#protocol JackClient  
  
@interface Test : NSObject<Client>{  
    id<Client> client;  
}  
-(id)initWithClient:(id<Client>) client;  
-(void) turnTheCrank;  
@property(retain) id<Client> client;  
  
@end  
  
@implementation Test  
  
-(id)initWithClient:(id<Client>)client{  
    self = [super init];  
    if (self) {  
        _client = client;  
    }  
    return self;  
}  
  
-(void) turnTheCrank{  
    [self.client defaultMethod];  
    [self.client required];  
    if ([self.client respondsToSelector:@selector(optional)]) {//可选回调可先判断是否实现，再调用  
        [self.client optional];  
    }  
}  
  
@end  

[[[Test alloc]initWithClient:[[JackClient alloc] init]] turnTheCrank];