HarmonyOS NavPathStack的长度如何监控

@Provide('NavPathStack') @Watch('onPageInfosUpdated') pageInfos: NavPathStack = new NavPathStack() 
 
// @Watch 回调 
onPageInfosUpdated(propName: string): void { 
  console.info('test NavigationExample1 size:' + this.pageInfos.size()); 
}