1 协议，就是class里面必须遵循的约定。例如
@protocol viewControllerDelegate <NSObject>
-(void)loadMoreData;
@end
@interface ViewController ()<viewControllerDelegate>
@property (weak, nonatomic) IBOutlet UITableView *tableView;
@property (nonatomic,strong) NSMutableArray *materialArray;
@end
@implementation ViewController
//必须有loadMoreData
-(void)loadMoreData{}
@end
原文：http://www.cnblogs.com/lihaozhou/p/4430023.html