React中子组件向父组件传递状态：以倒计时组件为例实现父组件条件渲染

// CountDown 组件 (初始版本片段)
function CountDown(props) {
  const [countdown, setCountdown] = useState(props.seconds);
  const [onTime, setOnTime] = useState(true); // 子组件内部状态
  // ...
  useEffect(() => {
    if (countdown <= 0) {
      clearInterval(timertId.current);
      setOnTime(false); // 更新子组件内部状态
    }
  }, [countdown]);
  // ...
}

// QuestionCard.js (修改后)
import React, { useEffect, useState } from 'react';
import {
  Grid, Box, Card, CardContent, Typography,
  LinearProgress, ButtonGroup, ListItemButton, CardActions, Button
} from '@mui/material';
import CountDown from './CountDown'; // 确保路径正确
import useAxios from './useAxios'; // 假设存在此hook
import { baseURL_Q } from './config'; // 假设存在此配置

export default function QuestionCard() {
  const [questions, setQuestions] = useState([]);
  const [clickedIndex, setClickedIndex] = useState(0);
  const [currentQuestionIndex, setCurrentQuestionIndex] = useState(0);
  const [value, setValue] = useState(null);
  const { isLoading, error, sendRequest: getQuestions } = useAxios();
  const { sendRequest: getAnswers } = useAxios();
  const [onTime, setOnTime] = useState(true); // 父组件管理 onTime 状态

  // ... 其他处理函数和useEffect ...
  const handleSubmit = () => {
    setValue(true);
  };

  const handleSelectedItem = (index) => {
    setClickedIndex(index);
  };

  const handleChange = (e) => {
    setValue(e.target.value);
  };

  useEffect(() => {
    const transformQuestions = (questionObj) => {
      const loadedQuestions = [];

      for (const questionKey in questionObj) {
        loadedQuestions.push({
          id: questionKey,
          id_test: questionObj[questionKey].id_test,
          tipologia_domanda: questionObj[questionKey].tipologia_domanda,
          testo: questionObj[questionKey].testo,
          immagine: questionObj[questionKey].immagine,
          eliminata: questionObj[questionKey].eliminata,
        });
      }
      setQuestions(loadedQuestions);
    };
    getQuestions(
      {
        method: 'GET',
        url: baseURL_Q,
      },
      transformQuestions
    );
  }, [getQuestions]);

  let questionsTitle = questions.map((element) => `${element.testo}`);
  let questionId = questions.map((element) => `${element.id}`);

  // 假设 goToNext 是一个处理函数
  const goToNext = () => {
    // 处理下一题逻辑
    setCurrentQuestionIndex((prevIndex) => prevIndex + 1);
    setValue(null); // 重置选项
    setClickedIndex(0); // 重置点击状态
  };

  return (
    <Grid container spacing={1}>
      <Grid item xs={10}>
        <Box
          sx={{
            minWidth: 275,
            display: 'flex',
            alignItems: 'center',
            paddingLeft: '50%',
            paddingBottom: '5%',
            position: 'center',
          }}
        >
          <Card
            variant='outlined'
            sx={{
              minWidth: 400,
            }}
          >
            <CardContent>
              <Grid container spacing={0}>
                <Grid item xs={8}>
                  <Typography
                    variant='h5'
                    component='div'
                    fontFamily={'Roboto'}
                  >
                    Nome Test
                  </Typography>
                </Grid>
                <Grid item xs={4}>
                  {/* 将 setOnTime 函数作为 props 传递给 CountDown */}
                  <CountDown seconds={300} setOnTime={setOnTime} />
                </Grid>
              </Grid>

              {/* 根据 onTime 状态进行条件渲染 */}
              {onTime ? (
                <>
                  <LinearProgress variant='determinate' value={1} />

                  <Typography
                    sx={{ mb: 1.5, mt: 1.5 }}
                    fontFamily={'Roboto'}
                    fontWeight={'bold'}
                  >
                    {questionsTitle[currentQuestionIndex]}
                  </Typography>

                  <ButtonGroup
                    fullWidth
                    orientation='vertical'
                    onClick={handleSubmit}
                    onChange={handleChange}
                  >
                    <ListItemButton
                      selected={clickedIndex === 1}
                      onClick={() => handleSelectedItem(1)}
                    >
                      Risposta 1
                    </ListItemButton>
                    <ListItemButton
                      selected={clickedIndex === 2}
                      onClick={() => handleSelectedItem(2)}
                    >
                      Risposta 2
                    </ListItemButton>
                    <ListItemButton
                      selected={clickedIndex === 3}
                      onClick={() => handleSelectedItem(3)}
                    >
                      Risposta 3
                    </ListItemButton>
                    <ListItemButton
                      selected={clickedIndex === 4}
                      onClick={() => handleSelectedItem(4)}
                    >
                      Risposta 4
                    </ListItemButton>
                  </ButtonGroup>
                </>
              ) : (
                <Typography variant='h6' color='error' sx={{ mt: 2 }}>
                  时间到！
                </Typography>
              )}
            </CardContent>
            <CardActions>
              {onTime && ( // 只有在时间内才显示按钮
                <Button onClick={goToNext} disabled={!value} variant='contained' size='small'>
                  Avanti
                </Button>
              )}
            </CardActions>
          </Card>
        </Box>
      </Grid>
    </Grid>
  );
}

// CountDown.js (修改后)
import { Typography, Paper, Grid } from '@mui/material';
import React, { useEffect, useRef, useState } from 'react';

const formatTime = (time) => {
  let minutes = Math.floor(time / 60);
  let seconds = Math.floor(time - minutes * 60);

  // 格式化为两位数
  minutes = minutes < 10 ? '0' + minutes : minutes;
  seconds = seconds < 10 ? '0' + seconds : seconds;

  return minutes + ':' + seconds;
};

function CountDown(props) {
  const [countdown, setCountdown] = useState(props.seconds);
  // 移除子组件内部的 onTime 状态
  const timertId = useRef();

  useEffect(() => {
    timertId.current = setInterval(() => {
      setCountdown((prev) => prev - 1);
    }, 1000);
    // 清理函数，在组件卸载时清除定时器
    return () => clearInterval(timertId.current);
  }, []); // 空依赖数组确保只在组件挂载时运行一次

  useEffect(() => {
    if (countdown <= 0) {
      clearInterval(timertId.current);
      // 调用父组件传递过来的 setOnTime 函数
      props.setOnTime(false);
    }
  }, [countdown, props.setOnTime]); // 将 props.setOnTime 添加到依赖数组

  return (
    <Grid container>
      <Grid item xs={5}>
        <Paper elevation={0} variant='outlined' square>
          <Typography component='h6' fontFamily={'Roboto'}>
            Timer:
          </Typography>
        </Paper>
      </Grid>
      <Grid item xs={5}>
        <Paper
          elevation={0}
          variant='outlined'
          square
          sx={{ bgcolor: 'lightblue' }}
        >
          <Typography component='h6' fontFamily={'Roboto'}>
            {formatTime(countdown)}
          </Typography>
        </Paper>
      </Grid>
    </Grid>
  );
}

export default CountDown;