[]ProgressBar 代码问题

依照官网教程https://layaair.ldc.layabox.com/demo/?2d&UI&ProgressBar 

使用会出现<<<TypeError: Cannot read property 'value' of undefined>>>

我的代码为按钮点击后
出现popup并且模拟进度条加载

按钮代码:
this.testLoadingBar_anim.on(Event.CLICK,this,()=>{
    var loading : Onloading = new Onloading();
    loading.popup(true);
    Laya.timer.loop(100, this, loading.changeValue);
});
进度条代码:
import Handler = Laya.Handler;
export class Onloading extends ui.LoadingUI{
       constructor(){
       super();
       this.loadingBar.changeHandler = new Handler(this, this.onChange);
}
public changeValue():void{
       console.log("change");
       if (this.loadingBar.value >= 1){
                this.loadingBar.value = 0;
       }
            this.loadingBar.value += 0.05;
       }
       onChange(value: number): void {
            console.log("进度：" + Math.floor(value * 100) + "%");
        }
}