HarmonyOS 如何watch viewmodel中的数据变化显示对话框

viewmodel模式有个对话框根据请求网络还是请求缓存来决定是否显示，所有这个loadingPageStatus需要放到viewmodel中。但是如何watch他的变化来显示对话框，代码如下：

import { NavigationManager } from '@cmb/router';
import hilog from '@ohos.hilog';

@Component
export struct Page {
  build() {
    NavDestination() {
      RelativeContainer() {
        Button('跳转至测试页')
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
          .alignRules({
            center: { anchor: '__container__', align: VerticalAlign.Center },
            middle: { anchor: '__container__', align: HorizontalAlign.Center }
          })
      }
      .height('100%')
      .width('100%')
      .onClick(() => {
        NavigationManager.getNavPathStack().pushDestinationByName('web', undefined)
      })
    }
    .onAppear(() => {
      hilog.debug(1, "NavigationTest", "onAppear0");
    })
    .onDisAppear(() => {
      hilog.debug(1, "NavigationTest", "onDisAppear0");
    })
    .onShown(() => {
      hilog.debug(1, "NavigationTest", "onShow0");
    })
    .onHidden(() => {
      hilog.debug(1, "NavigationTest", "onHidden0");
    })
    .title("首页")
  }
}

@Entry
@Component
struct Index {
  @State message: string = '测试Navigation生命周期';

  aboutToAppear() {
    let modules: string[] = ["@cmb/module1"]
    modules.forEach(async (value: string, index: number, array: string[]) => {
      let ns: ESObject = await import(value);
      ns.dynamicImport("");
    })
  }

  @Builder
  routerMap(builderName: string, param: object) {
    // Obtain the WrappedBuilder object based on the module name, create a page through the builder interface, and import the param parameter.
    NavigationManager.getBuilder(builderName).builder(param);
  };

  build() {
    Navigation(NavigationManager.getNavPathStack()) {
      NavDestination() {
        Page().width("100%").height("100%")
      }
      .onShown(() => {
        console.log("首页onShow")
      })
      .onHidden(() => {
        console.log("首页onHidden")
      })
      .onAppear(() => {
        console.log("首页onAppear")
      })
    }
    .mode(NavigationMode.Stack)
    .hideToolBar(true)
    .hideBackButton(true)
    .hideTitleBar(true)
    .navDestination(this.routerMap)
  }
}