协议1

//结构：

//main.m

#import <Foundation/Foundation.h>
#import "Rent1.h"
#import "Rent2.h"
#import "Rent3.h"
#import "Person.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
     
        Person *xiaowang=[[Person alloc]init];
        
        Rent1 *r1=[[Rent1 alloc]init];
        r1.name=@"Li";
        Rent2 *r2=[[Rent2 alloc]init];
        r2.name=@"叶良辰";
        Rent3 *r3=[[Rent3 alloc]init];
        r3.name=@"赵日天";
        
        xiaowang.obj=r1;
        
        [xiaowang needHouse];
     
    }
    return 0;
}

//RentPototol.h《协议》

#import <Foundation/Foundation.h>

@protocol RentPototol <NSObject>
@optional
-(void)rentHouse;

@end

//Person.h

#import <Foundation/Foundation.h>
#import "RentPototol.h"
@interface Person : NSObject

@property(nonatomic,strong)NSString *myName;
@property(nonatomic,assign)id<RentPototol> obj;

-(void)needHouse;

@end

//Person.m

#import "Person.h"
#import "RentPototol.h"

@implementation Person

-(void)needHouse
{
    if ([_obj respondsToSelector:@selector(rentHouse)]) {
        [_obj rentHouse];
    }
    else
    {
        NSLog(@"臣妾做不到呀！");
    }
}
@end

//Rent1.h

#import <Foundation/Foundation.h>
#import "RentPototol.h"

@interface Rent1 : NSObject<RentPototol>
@property(nonatomic,copy)NSString *name;

@end

//Rent1.m

#import "Rent1.h"

@implementation Rent1

-(void)rentHouse
{
    NSLog(@"我是%@，我打电话找房源",_name);
}

@end

//Rent2.h

#import <Foundation/Foundation.h>
#import "RentPototol.h"

@interface Rent2 : NSObject<RentPototol>
@property(nonatomic,copy)NSString *name;

@end

//Rent2.m

#import "Rent2.h"

@implementation Rent2

-(void)rentHouse
{
    NSLog(@"我是%@，我打电话找房源",_name);
}

@end

//Rent3.h

#import <Foundation/Foundation.h>
#import "RentPototol.h"

@interface Rent3 : NSObject<RentPototol>

@property(nonatomic,copy)NSString *name;

@end

//Rent3.m

#import "Rent3.h"

@implementation Rent3

//并没有提供租住的能力，无法实现声明的协议要求

@end

//结果

2015-11-10 19:18:15.737 RentHouse[7738:124003] 我是Li，我打电话找房源