问在swift中为UITableView加载更多内容

EN

var allObjectArray: NSMutableArray = []
var elements: NSMutableArray = []

var currentPage = 0
var nextpage = 0

override func viewDidLoad() {
    super.viewDidLoad()
    for var i = 0; i <= 500; i++ {
        allObjectArray.addObject(i)
    }
    elements.addObjectsFromArray(allObjectArray.subarrayWithRange(NSMakeRange(0, 20)))
}
override func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
        println(indexPath.row)
        nextpage = elements.count - 5
        if indexPath.row == nextpage {
            currentPage++
            nextpage = elements.count - 5
            elements.addObjectsFromArray(allObjectArray.subarrayWithRange(NSMakeRange(currentPage, 20)))
                tableView.reloadData()
        }
    }