[_tableView setPullToRefreshHandler:^{
        //从第一行数据开始加载
        _offset = 1;
        [self startDownloadData];
    }];
    
    [_tableView setPullToLoadMoreHandler:^{
        _offset += _pageSize;
        [self startDownloadData];
    }];

//如果偏移值为1,刷新数据    
    if(_offset == 1)
    {
        NSLog(@"下拉刷新!");
        [_dataArray removeAllObjects];
    }
    
 NSArray *list = [doc nodesForXPath:@"//promotion" error:nil];

//遍历数据,并赋值
    for(GDataXMLElement *promotion in list)
    {
        PromotionModel *model = [[PromotionModel alloc] init];
        model.id = [[[promotion elementsForName:@"id"] firstObject] stringValue];
        model.name = [[[promotion elementsForName:@"name"] firstObject] stringValue];
        
        [_dataArray addObject:model];
    }

    //结束刷新
    [_tableView refreshFinished];
    

    [_tableView loadMoreFinished];
    
    [_tableView reloadData];