iOS nsurl使用 get数据

NSString *urlStr = [NSString stringWithFormat:@"devid=%@&haoma=%@",devIDString,[_key objectAtIndex:indexPath.row]];    NSError *err;    NSString *nurl = [[checkfollow_url stringByAppendingString:urlStr] stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];    NSString *upre=[NSString stringWithContentsOfURL:[NSURL URLWithString:nurl] encoding:NSUTF8StringEncoding error:&err];