Telerik RadListView for Nativescript未显示

我在Telerik UI中为Nativescript免费库显示RadListView时遇到问题 . 我从入门指南中实施了样本：http://docs.telerik.com/devtools/nativescript-ui/Controls/NativeScript/ListView/getting-started

XML：

<Page loaded="onPageLoaded" xmlns:lv="nativescript-telerik-ui/listview" xmlns="http://www.nativescript.org/tns.xsd">
    <lv:RadListView items="{{ dataItems }}" >
        <lv:RadListView.listViewLayout>
            <lv:ListViewLinearLayout scrollDirection="Vertical"/>
        </lv:RadListView.listViewLayout>
        <lv:RadListView.itemTemplate>
            <StackLayout orientation="vertical">
                <Label fontSize="20" text="{{ itemName }}"/>
                <Label fontSize="14" text="{{ itemDescription }}"/>
            </StackLayout>
        </lv:RadListView.itemTemplate>
    </lv:RadListView>
</Page>

代码隐藏：

import viewModel = require("./getting-started-model");
export function onPageLoaded(args){
    var page = args.object;
    page.bindingContext = new viewModel.ViewModel();
}

模型：

import {ObservableArray} from "data/observable-array";
import timer = require("timer");

export class ViewModel {

    private _items: ObservableArray<DataItem>;
    private _words = ["One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten"];

    constructor() {
    }

    get dataItems() {
        if (!this._items) {
            this._items = new ObservableArray<DataItem>();

            for (var i = 0; i < 10; i++) {
                this._items.push(new DataItem(i, "Item " + i, "This is item description."));
            }
        }
        return this._items;
    }

    private getRandomLengthString(){
        var sentenceLength = Math.round((Math.random() * 15));
        var result = this._words[0];
        for (var i = 0; i < sentenceLength; i++){
            result += (this._words[i % this._words.length] + " ");
        }
        return result;
    }
}

export class DataItem {
    public id: number;
    public itemName;
    public itemDescription;

    constructor(id: number, name: string, description: string) {
        this.id = id;
        this.itemName = name;
        this.itemDescription = description;
    }
}

但我得到的只是空白页面..我正在使用NS版本2.3.0

我究竟做错了什么？