/* 

 __block void (^callback)() = [^{ 


 float second = 2.0; 

 bool _stop = NO; 

 if(_stop) { 

 NSLog(@"all done"); 

 callback = nil; // break retain cycle 

 } else { 

 NSLog(@"still going"); 

 NSMutableDictionary *dic = [[NSMutableDictionary alloc]init]; 


 [dic setObject:object forKey:key]; 



 [_service listMessages:^(id response, NSError *error) { 

 //获取主线程，更新界面 

 if (error) { 

 //show error 

 }else{ 

 获取数据 


 } 

 dispatch_async(dispatch_get_main_queue(), ^{ 

 //更新界面 

 [table reloadData]; 

 [self scrollTableToFoot]; 

 }); 

 } 



 } parameters:dic]; 

 dispatch_after(dispatch_time(DISPATCH_TIME_NOW, second * NSEC_PER_SEC), 

 dispatch_get_main_queue(), 

 callback); 

 } 

 } copy]; 


 dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2.0 * NSEC_PER_SEC), 

 dispatch_get_main_queue(), 

 callback); 

 */