查询列表，返回前20个数据：

//创建BmobQuery实例，指定对应要操作的数据表名称    BmobQuery *query = [BmobQuery queryWithClassName:className];    //按updatedAt进行降序排列    [query orderByDescending:@"updatedAt"];    //返回最多20个结果    query.limit = 20;    //执行查询    [query findObjectsInBackgroundWithBlock:^(NSArray *array, NSError *error) {        //处理查询结果        for (BmobObject *obj in array) {            News *info    = [[News alloc] init];            if ([obj objectForKey:@"title"]) {                info.title    = [obj objectForKey:@"title"];            }            if ([obj objectForKey:@"describe"]) {                info.content  = [obj objectForKey:@"describe"];            }            if ([obj objectForKey:@"phone"]) {                info.phoneNum = [obj objectForKey:@"phone"];            }            info.time     = [_dateFormatter stringFromDate:obj.updatedAt];            [_infoMutableArray addObject:info];        }        [_tableView reloadData];    }];