这个_OpenUI5演练中的helloDialog

我正在openUi5网站上进行演练演示 OpenUI5 walkthrough demo

我通过以下代码:

sap.ui.define([
    "sap/ui/core/UIComponent",
    "sap/ui/model/json/JSONModel",
    "sap/ui/demo/wt/controller/HelloDialog"
], function(UIComponent, JSONModel, HelloDialog) {
    "use strict";
    return UIComponent.extend("sap.ui.demo.wt.Component", {
        metadata: {
            manifest: "json"
        },
        init: function() {
            // call the init function of the parent
            UIComponent.prototype.init.apply(this, arguments);
            // set data model
            var oData = {
                recipient: {
                    name: "World"
                }
            };
            var oModel = new JSONModel(oData);
            this.setModel(oModel);

            // set dialog
            this._helloDialog = new HelloDialog(this.getRootControl());
        },

        openHelloDialog: function() {
            this._helloDialog.open();
        }
    });
});

我有点怀疑 this._helloDialog = new HelloDialog(this.getRootControl());

_helloDialog 没有定义,我们使用的是严格模式,那么为什么系统不抛出这样的消息呢 _helloDialog is undefined