HarmonyOS 如何检测当前APP是在前台还是后台？

onPageShow(): void { 
  window.getLastWindow(getContext(this), (err,win) => { 
     win.on("windowEvent", (event) => { 
         console.log(JSON.stringify(event)); 
     }) 
  }) 
}
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windowStage.on('windowStageEvent',(data) =>{ 
  console.info('Succeeded in enabling the listener for window stage event changes. Data: ' + 
  JSON.stringify(data)); 
})
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