通过继承nsoperation的方法--处理复杂任务

#import <Foundation/Foundation.h>
@class TTOperation;
@protocol TTOperationDelegate <NSObject>

-(void)operationComplete:(NSData *)data;

@end
@interface TTOperation : NSOperation
@property(nonatomic,weak)id<TTOperationDelegate>delegate;
@end
import "TTOperation.h"

@implementation TTOperation
//重写main方法
-(void)main
{
    [super main];
    NSData *firstData=[NSData dataWithContentsOfURL:[NSURL URLWithString:KURL1]];

    dispatch_async(dispatch_get_main_queue(), ^{

        if (_delegate&&[_delegate respondsToSelector:@selector(operationComplete:)]) {
            [_delegate operationComplete:firstData];
        }
    });

}
@end