1

我对 React 几乎是新手。在这个应用程序中，我正在使用 Hooks！我制作了一个倒数计时器，它会在登录后几秒钟内显示出来。我无法让它在单击按钮时停止。我需要一些建议，因为过去两天我一直在为此苦苦挣扎。到目前为止，这是我的代码：（请帮助）

function Admin() {
    const [isTimerOpen, setTimmer] = useState(false);
    let history = useHistory();

    // SET BY THE ADMIN
    var minutesToCountDown = 0.9;
    // TRANSFORM INTO SECONDS
    var transformMinutesToSeconds = minutesToCountDown * 60
    // KEEP A STATE
    const [counterValue, setCounterValue] = useState(0);
    const [isTimmerStoped, setStopTimer] = useState(false);

    // FUNCTION TO HAPPEN EVERY 1 SECOND
    function timeIt() {
        if (isTimmerStoped === false) {
            transformMinutesToSeconds--
            setCounterValue(transformMinutesToSeconds)
            console.log("Timer is on: ", transformMinutesToSeconds)

            if (transformMinutesToSeconds === 0) {
                clearInterval(interval)
                setStopTimer(true)
            }
        } else {
            setStopTimer(true)
            clearInterval(interval)
        }
    }

    // STARTS THE COUNTDOWN
    var interval;
    const startCountdown = () => {
        interval = setInterval(timeIt, 1000)
    }

    const stopCountdown = () => {
        console.log("Stop Timer")
        setStopTimer(true);
        setCounterValue(0);
        setTimmer(false);
    }

    // ADD 0 IN FRONT ON THE TIME REMAINING
    const addLeadingZeros = value => {
        value = String(value);
        while (value.length < 2) {
            value = `0${value}`;
        }
        return value;
    };

    // CONVERT SECONDS INTO TIME REMAINING
    function convertSeconds(seconds) {
        var min = Math.floor(seconds / 60);
        var sec = seconds % 60;
        return addLeadingZeros(min) + ':' + addLeadingZeros(sec)
    }

    const logOutUser = () => {
        logout();
        return history.push(mainRoute)
    }

    function setTimer() {
        const timer = setTimeout(() => {
            setTimmer(true)
            console.log('This will run after 3 seconds!')
            startCountdown()

        }, sessionTimeout);
        return () => clearTimeout(timer);
    }

    useEffect(() => {
        if (isTimmerStoped === false) {
            console.log('Effect Starting', isTimmerStoped)
            setTimer()
        } else {
            console.log('Effect Stopping', isTimmerStoped)
            stopCountdown()
        }

      }, [isTimmerStoped, setStopTimer, minutesToCountDown]);



    return <React.Fragment>
            <CssBaseline />
            <Container disableGutters maxWidth={false}>
                <NavigationBar handleSignOut={logOutUser}/>
                <TimerContent 
                    timeRemaining={convertSeconds(counterValue)}
                    isTimerAlertOpen={isTimerOpen}
                    extendSessionBtn={stopCountdown}
                    logoutBtn={logOutUser}  
                    clickOutsideButton={stopCountdown}/>
            </Container>
    </React.Fragment>  
}

export default Admin;
4

2 回答 2

2

您不应该在函数变量中维护 setInterval 返回的 intervalId，因为它将在重新渲染时重置，并且您将丢失实际的计时器 ID。您必须改为使用useRef钩子来存储 timerId

   const interval = useRef(null);
    ...
   function timeIt() {
        if (isTimmerStoped === false) {
            transformMinutesToSeconds--
            setCounterValue(transformMinutesToSeconds)
            console.log("Timer is on: ", transformMinutesToSeconds)

            if (transformMinutesToSeconds === 0) {
                clearInterval(interval.current)
                setStopTimer(true)
            }
        } else {
            setStopTimer(true)
            clearInterval(interval.current)
        }
    }
    ...
   // STARTS THE COUNTDOWN
    const startCountdown = () => {
        interval.current = setInterval(timeIt, 1000)
    }
于 2020-05-04T18:40:52.460 回答
2

你应该做两件事。

  1. 使interval变量成为参考。这样，它的价值在它导入的每个地方都是独一无二的。注意：仅仅在组件上方创建一个变量是一个坏主意，因为该变量将在导入该Admin组件的每个组件之间共享，这将导致错误。

错误的

let interval;

function Admin() {
  //... code here

  // STARTS THE COUNTDOWN
  // var interval; Remove from here
  const startCountdown = () => {
      interval = setInterval(timeIt, 1000)
  }

  //... code here
}

export default Admin;

对

function Admin() {
  const interval = React.useRef(); 
  //... code here

  // STARTS THE COUNTDOWN
  // var interval; Remove from here
  const startCountdown = () => {
      interval.current = setInterval(timeIt, 1000)
  }

  //... code here
}

export default Admin;
  1. 添加clearInterval到您的stopCountdown功能。您可以删除timeIt函数中的 clearInterval 并将其移至stopCountdown. 请看一下我为演示而制作的这个代码笔
const stopCountdown = () => {
  console.log("Stop Timer")
  setStopTimer(true);
  setCounterValue(0);
  setTimmer(false);
  clearInterval(interval.current) // Clear the interval here
}
于 2020-05-04T18:42:38.823 回答