类似Java的泛型与接口的结合体，用于类型的<>中，可以多继承（按照OC的说法叫遵从某些协议）
1、定义协议
@protocol Client <NSObject>
-(void)defaultMethod;//默认必须实现 @required//必须
-(void)required； @optional//可选
-(void)optional;
@end
2、符合（实现）协议
#import "Client.h"
@interface JackClient : NSObject<Client> @end @implementation JackClient
-(void)defaultMethod{
NSLog(@"this is defaultMethod");
} -(void)required{
NSLog(@"this is required method");
}
@end
3、使用并调用回调
#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
最后
[[[Test alloc]initWithClient:[[JackClient alloc] init]] turnTheCrank];