[]List滚动条问题

按照示例程序写了个list，出现两个问题：
1. list不能滚动
2. list item里的button图片显示不出来

item代码如下：

(function (_super){

    function MarketItem()

    {

        MarketItem.__super.call(this);



        this.size(312, 462);



        // {id:1,name:"10金豆-测试",price:0.01,title:"10金豆-测试",desc:"测试",balance:10,gift:0,imgPath:"res\\common\\BalanceSellDlg\\xiaodou.png",hot:1,orderCount:9}



        // 背景

        var bg_image = new Laya.Image();

        bg_image.skin = "res/popupwnd/market_item_bg.png";

        bg_image.pos(0, 0);

        bg_image.size(312, 462);

        this.addChild(bg_image);



        // 金豆数

        this._goldLabel = new Laya.Label();

        this._goldLabel.color = "#FFBA00";

        var font = GameUI.GetFont("$font.marketdlg.default");

        this._goldLabel.font = font.family;

        this._goldLabel.bold = (parseInt(font.bold | 0) == 0 ? false : true);

        this._goldLabel.fontSize = parseInt(font.size);

        this._goldLabel.underline = (parseInt(font.underline | 0) == 0 ? false : true);

        this._goldLabel.align = "center";

        this._goldLabel.valign = "middle";

        this._goldLabel.pos(0, 50);

        this._goldLabel.size(312, 20);

        this.addChild(this._goldLabel);



        // 金豆图片

        this._goldImage = new Laya.Image();

        this.addChild(this._goldImage);



        // 购买按钮

        this._goldButton = new Laya.Button();

        this._goldButton.skin = "res/popupwnd/btn_buygold.png";

        this._goldButton.labelFont = font.family;

        this._goldButton.labelBold = (parseInt(font.bold | 0) == 0 ? false : true);

        this._goldButton.labelSize = parseInt(font.size);

        this._goldButton.labelColors = "#FFFFFF,#FFFFFF,#FFFFFF,#EEEEEE";

        this._goldButton.stateNum = 1;

        this._goldButton.pos(75, 350);

        this.addChild(this._goldButton);



        this.setGold = function(gold)

        {

            this._goldLabel.text = "×" + gold + "金豆";

        };



        this.setGoldImage = function(img)

        {

            this._goldImage.skin = img;

            this._goldImage.pos((312-this._goldImage.width)/2, (462-this._goldImage.height)/2);

        };



        this.setPrice = function(price)

        {

            this._goldButton.label = "RMB " + price;

        };

    }

    Laya.class(MarketItem, "xgame.marketitem", _super);

})(Laya.Box);

list代码如下：

var list = new Laya.List();

list.itemRender = xgame.marketitem;

list.repeatX = 3;

list.repeatY = 1;

list.spaceX = 10;

list.hScrollBarSkin = "";

//list.vScrollBarSkin = "";

list.pos((BalanceMarketDlg.width-312*3-10*2)/2, 120);

list.selectEnable = true;

list.renderHandler = new Laya.Handler(this, UpdateMarketItem);

Laya.stage.addChild(list);

list.array = that._items;

updateitem代码如下：

function UpdateMarketItem(cell, index)

{

    // {id:1,name:"10金豆-测试",price:0.01,title:"10金豆-测试",desc:"测试",balance:10,gift:0,imgPath:"res\\common\\BalanceSellDlg\\xiaodou.png",hot:1,orderCount:9}

    cell.setGold(cell.dataSource.balance + cell.dataSource.gift);

    cell.setGoldImage(cell.dataSource.imgPath);

    cell.setPrice(cell.dataSource.price);

}