HarmonyOS 在组件或类中内如何监听前后台切换

可以试着在UIAbility中的onForeground和onBackground用AppStorage.setOrCreate<boolean>('view', true)来监听应用前后台。https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/uiability-lifecycle-V5#foreground%E5%92%8Cbackground%E7%8A%B6%E6%80%81

在组件中监听这个值的变化，参考demo：

@Entry
@Component
struct Index {
  @State message: string = 'Hello World'
  @StorageLink('view') isOnForeground:boolean = true
  build() {
    Row() {
      Column() {
        Text(this.message)
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
        Vid({isOnForeground:this.isOnForeground})
      }
      .width('100%')
    }
    .height('100%')
  }
}
@Component
struct Vid {
  @Watch('change')@Link isOnForeground:boolean
  @State message: string = 'video'
  build() {
    Text("message")
      .fontSize(50)
      .fontWeight(FontWeight.Bold)
      .onClick(()=>{
        this.message += this .isOnForeground
        console.info(""+this.isOnForeground)
      })
  }
  change() {
    if (this.isOnForeground) {
      console.info('in header')
    } else {
      console.info('in end')
    }
  }
}