带反应钩子的倒计时器

Question

我正在尝试自己实现倒计时器，只是为了更多地了解钩子。我知道那里有图书馆，但不想使用它。我的代码的问题是，我无法在“计时器”函数内获取更新的状态，该函数在启动计时器函数中更新我正在尝试实现计时器，该计时器将具有启动、停止和恢复的触发器，并且可以手动触发。由使用倒计时组件的其他组件

import React, { useState } from 'react';

const Countdown = ({ countDownTimerOpt }) => {
  const [getObj, setObj] = useState({
    formatTimer: null,
    countDownTimer: 0,
    intervalObj: null,
  });

  const { formatTimer, countDownTimer, intervalObj } = getObj;

  if (countDownTimerOpt > 0 && intervalObj === null) {
    startTimer();
  }

  function startTimer() {
    const x = setInterval(() => {
      timer();
    }, 1000);

    setObj((prev) => ({
      ...prev,
      countDownTimer: countDownTimerOpt,
      intervalObj: x,
    }));
  }

  function timer() {
    var days = Math.floor(countDownTimer / 24 / 60 / 60);
    var hoursLeft = Math.floor(countDownTimer - days * 86400);
    var hours = Math.floor(hoursLeft / 3600);
    var minutesLeft = Math.floor(hoursLeft - hours * 3600);
    var minutes = Math.floor(minutesLeft / 60);
    var remainingSeconds = countDownTimer % 60;

    const formatTimer1 =
      pad(days) +
      ':' +
      pad(hours) +
      ':' +
      pad(minutes) +
      ':' +
      pad(remainingSeconds);

    if (countDownTimer === 0) {
      clearInterval(intervalObj);
    } else {
      setObj((prev) => ({
        ...prev,
        formatTimer: formatTimer1,
        countDownTimer: prev['countDownTimer'] - 1,
      }));
    }
  }
  function pad(n) {
    return n < 10 ? '0' + n : n;
  }

  return <div>{formatTimer ? formatTimer : Math.random()}</div>;
};
export default Countdown;

import React, { useState, useEffect } from 'react';
import Timer from '../../components/countdown-timer/countdown.component';

const Training = () => {
  const [getValue, setValue] = useState(0);

  useEffect(() => {
    const x = setTimeout(() => {
      console.log('setTimeout');
      setValue(10000);
    }, 5000);

    return () => clearInterval(x);
  }, []);

  return <Timer countDownTimerOpt={getValue} />;

不想在训练页面内使用任何设置的间隔，因为倒计时组件也将在考试页面中使用

Answer 1

通常使用钩子时，我会将您的功能组合到自定义钩子中，并在不同的地方使用它。

const useTimer = (startTime) => {
    const [time, setTime] = useState(startTime)
    const [intervalID, setIntervalID] = useState(null)
    const hasTimerEnded = time <= 0
    const isTimerRunning = intervalID != null

    const update = () => {
        setTime(time => time - 1)
    }
    const startTimer = () => {
        if (!hasTimerEnded && !isTimerRunning) {
            setIntervalID(setInterval(update, 1000))
        }
    }
    const stopTimer = () => {
        clearInterval(intervalID)
        setIntervalID(null)
    }
    // clear interval when the timer ends
    useEffect(() => {
        if (hasTimerEnded) {
            clearInterval(intervalID)
            setIntervalID(null)
        }
    }, [hasTimerEnded])
    // clear interval when component unmounts
    useEffect(() => () => {
        clearInterval(intervalID)
    }, [])
    return {
        time,
        startTimer,
        stopTimer,
    }
}

您当然可以添加重置功能或进行其他更改，但使用可能如下所示：

const Training = () => {
    const { time, startTimer, stopTimer } = useTimer(20)
    return <>
        <div>{time}</div>
        <button onClick={startTimer}>start</button>
        <button onClick={stopTimer}>stop</button>
    </>
}