案例：找房子（代理设计模式）

//1:协议声明:
#import <Foundation/Foundation.h>  
@protocol FindApartment <NSObject> 
　　-(void)findApartment;
@end

//2:代理角色声明(Agent.h)头文件声明
#import <Foundation/Foundation.h> 
#import "FindApartment.h" 
    @interface Agent : NSObject <FindApartment> 
@end

//3:代理角色实现（Agent.m）实现文件
#import "Agent.h" 
@implementation Agent 
-(void)findApartment{     
    NSLog(@"findApartment"); 
} 
@end

//4:真实角色声明（Person.h）头文件声明
#import <Foundation/Foundation.h>
#import "FindApartment.h" 
@interface Person : NSObject {   
  @private     NSString *_name;    
  id<FindApartment> _delegate; //委托人(具备中介找房子的协议) 
}
@property(nonatomic,copy) NSString *name;
@property(nonatomic,assign)id<FindApartment> delegate; 
-(id)initWithName:(NSString *)name withDelegate:(id<FindApartment>) delegate;
-(void)wantToFindApartment;
@end

//5:真实角色实现（Person.m）实现
#import "Person.h" 
//定义私有方法 
@interface Person()
 -(void)startFindApartment:(NSTimer *)timer; 
@end 
@implementation Person
 @synthesize name=_name; 
 @synthesize delegate=_delegate;
 -(id)initWithName:(NSString *)name withDelegate:(id<FindApartment>) delegate{     
    self=[super init];     
    if(self){         
        self.name=name;         
        self.delegate=delegate;     
    }    
    return self; 
 } 
 -(void)wantToFindApartment{     
    [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(startFindApartment:) userInfo:@"Hello" repeats:YES];     
 }  
 -(void)startFindApartment:(NSTimer *)timer{    
     //NSString *userInfo=[timer userInfo];     
    [self.delegate findApartment];
 }
@end

//6:测试代理main.m方法
#import <Foundation/Foundation.h> 
#import "Person.h" 
#import "Agent.h"
int main(int argc, const char * argv[]) {     
 @autoreleasepool {                  
    // insert code here...         
    NSLog(@"Hello, World!");         
    Agent *agent=[[Agent alloc]init];         
    Person *jack=[[Person alloc]initWithName:@"jack" withDelegate:agent];         
    [jack wantToFindApartment];         
    [[NSRunLoop currentRunLoop]run];         
    [jack autorelease];     
 }     
 return 0; 
}