AppState 总是在定时器上触发

Question

我正在后台为运行构建一个计时器

我正在使用 React Native 和 Expo 构建应用程序

现在我正在使用的计时器我正试图让它在后台“运行”

为此，我使用 AppState 和一个事件监听器，获取开始时间和经过的时间（在应用程序最小化时详细说明）然后重新计算经过的时间并将其添加到计时器

Timer中有开始、暂停、重置和完成按钮

我不想开始工作的是，如果单击暂停按钮，经过的时间不能设置为设置状态，无论我在那里放了多少 IF，时间总是会改变

  const appState = useRef(AppState.currentState);
const [timerOn, setTimerOn] = useState(false);
const [time, setTime] = useState(0);
const [Paused,isPaused] = useState("");




const getElapsedTime = async () => {
  try {
    
    const startTime = await AsyncStorage.getItem("@start_time");
    const now = new Date();
    return differenceInSeconds(now, Date.parse(startTime));
    
  
  } catch (err) {
    
    console.warn(err);
  }
};


const recordStartTime = async () => {
  try {
    const now = new Date()
    await AsyncStorage.setItem("@start_time", now.toISOString());
  } catch (err) {
    console.warn(err);
  }
};


useEffect(() => {
  
 Timer()


}, []);

function Timer(){

  if(Paused == "no"){
   
  AppState.addEventListener("change", handleAppStateChange);
   return () => AppState.removeEventListener("change", handleAppStateChange);
  
  
  
  
  }
  else{
    console.log("eVENT lISTNER")
  }



}```

const handleAppStateChange = async (nextAppState) => {

  if (appState.current.match(/inactive|background/) &&
    nextAppState == "active" && Paused == "no") {
      // We just became active again: recalculate elapsed time based 
    // on what we stored in AsyncStorage when we started.
    const elapsed = await getElapsedTime();
    // Update the elapsed seconds state
//THE BELOW STATE IS UPDATED TO "ELAPSED" EVENTHOUGH IN THE IF STATEMENT ABOVE SAYS "PAUSED = NO" 
    setTime(elapsed);
        }
        else{
          console.log("YES")
        }
      
  appState.current = nextAppState;
};

  useEffect(() => {
    let interval = null;
  
    if (timerOn) {
      interval = setInterval(() => {
        setTime((prevTime) => prevTime + 1);
      }, 1000);
    } else if (!timerOn) {
      clearInterval(interval);
    }
  
    return () => clearInterval(interval);
  }, [timerOn]);

  let MyHour = ("0" + Math.floor((time / 3600))).slice(-2);
let MyMinutes =("0" + Math.floor((time / 60) % 60)).slice(-2);
let MySeconds = ("0" + ((time % 60))).slice(-2);

function TimerBtn(){
 isPaused("no")
  setTimerOn(true)
  recordStartTime()
}


function PauseBtn(){
isPaused("yes")
  setTimerOn(false)

}
function ResetBtn(){

  setTimerOn(false)
  setTime(0)
}
function DoneBtn(){


}

Answer 1

您的问题可能是您无法在侦听器中访问 Paused 的当前状态。阅读此答案以获得详细说明要变通，请改用引用 (useRef)。

const [Paused,isPaused] = useState("");

到

const isPaused = useRef(true); // use booleans instead of "yed"/"no"

请记住，要读取和写入引用，您必须将“.current”附加到引用，例如：

isPaused.current = true;
// or
if (isPaused.current) {...}

AppState 总是在定时器上触发

AppState Always firing on Timer

react-native

expo