async_table_refresh_issue_with_nsoperation.md

@interface AsyncTable()

@property(nonatomic, strong) NSMutableArray* alphaKeys;
@property(nonatomic, strong) NSOperationQueue *serialQueue;

@end

@implementation AsyncTable    

-(void)refreshData {
        [self.serialQueue cancelAllOperations];
        
        __block NSMutableArray* tempAlphaKeys;
        NSBlockOperation *op = [[NSBlockOperation alloc] init];

        op.completionBlock = ^{
            if (!op.isCancelled) {
              dispatch_async(dispatch_get_main_queue(), ^{
                  [self.alphaKeys removeAllObjects];
                  [self.alphaKeys addObjectsFromArray:tempAlphaKeys];
                
                  [table reloadData];
              });
            }
        };

        [op addExecutionBlock:^{
            tempAlphaKeys = <load data>;
        }];
        
        [self.serialQueue addoperation:op];
}
...
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return self.alphaKeys.count;
}
...
@end
}