创建一个Protocol，相当于java的接口，但，有些方法不必实现，例如以下

#import <Foundation/Foundation.h>

@protocol MyProtocol

@optional

- (void) test1;

- (void) test2;

- (void) test3;

@required

- (void) test4;

@end

继承了该协议，并声明在@optional下的代码方法不是必须实现的，但@required下的方法必须实现。

例如以下Book类

#import <Foundation/Foundation.h>

#import "MyProtocol.h"

@interface Book : NSObject <MyProtocol>

@property (nonatomic,assign) int price;

@end

#import "Book.h"

@implementation Book

- (void) test4

{

}

- (void) dealloc

{

    NSLog(@"Book is dealloc");

    [super dealloc];

}

@end

创建一个模拟买票样例。仅仅要实现了该接口 就可以作为买票代理人

#import <Foundation/Foundation.h>

@protocol TicketAgentProtocol <NSObject>

- (int) getTicketCount;

- (int) getTicketPrice;

@end

#import <Foundation/Foundation.h>

#import "TicketAgentProtocol.h"

@interface Person : NSObject

@property (nonatomic,retain) id<TicketAgentProtocol> delegate;

- (NSString *) buyTicket;

@end

#import "Person.h"

@implementation Person

- (NSString *) buyTicket

{

    return [NSString stringWithFormat:@"TICKET COUNT:%d ,TICKET PRICE:%d",

            [_delegate getTicketCount],[_delegate getTicketPrice]];

}

-(void)dealloc

{

    [_delegate release];

    [super dealloc];

}

@end

创建一个符合条件的“代理人”，就可以实现买票业务。

#import <Foundation/Foundation.h>

#import "TicketAgentProtocol.h"

@interface Other : NSObject <TicketAgentProtocol>

@end

#import "Other.h"

@implementation Other

- (int) getTicketCount

{

    return 1000;

}

- (int) getTicketPrice

{

    return 100;

}

@end

#import <Foundation/Foundation.h>

#import "TicketAgentProtocol.h"

#import "Person.h"

#import "Other.h"

int main(int argc, const char * argv[])

{

    @autoreleasepool {

        Person *p=[[[Person alloc] init] autorelease];

        Other *other=[[[Other alloc] init] autorelease];

        p.delegate=other;

        NSLog(@"%@",[p buyTicket]);

    }

    return 0;

}