[LayaAir 1.0]照着官方文档写的 Dialog 报错？

var LoadResource = function () {



    LoadResource.prototype.init = function () {

        this._container = new Sprite();

        Laya.stage.addChild(this._container);



		Laya.loader.load(["../bin/res/ui/progressBar.png", "../bin/res/ui/progressBar$bar.png"], Handler.create(this, this.onPreloaded));



    };

    

    LoadResource.prototype.onPreloaded = function () {

        

        this.initLoadData();

    };

    

    

    LoadResource.prototype.initLoadData = function () {

        var res_array = [

            {url:"res/ui/dialog.png",type:Laya.Loader.IMAGE},

            {url:"res/ui/close.png",type:Laya.Loader.IMAGE}

        ];

        

		Laya.loader.load(assets, Handler.create(this, onAssetLoaded));

        

    };

    

   

    LoadResource.prototype.onAssetLoaded = function () {

        

		var dialog = new Dialog();



		var bgImg = new Image("res/ui/dialog.png");

		dialog.addChild(bgImg);

        // bgImg.size(400, 458);



		var button = new Button("res/ui/close.png");

        button.size(50, 50);

		button.name = Dialog.CLOSE;

		button.pos(bgImg.width - button.width - 5, 5);

		dialog.addChild(button);



		dialog.dragArea = "0,0," + bgImg.width + "," + bgImg.height;

		dialog.show();

    };

}



Laya.class(LoadResource, "LoadResource", null);

照着官方文档实例， 写了一个显示 Dialog 代码， 怎么显示不出来？而且F12里输出报错：
Uncaught TypeError: Cannot read property 'visible' of undefined
 
不知道是什么情况？ 求指导。