我正在尝试新的React钩子,并有一个时钟组件,它的时间值应该每秒钟增加。但是,该值不会超过1。

function Clock() { const [time, setTime] = React.useState(0); React.useEffect(() => { const timer = window.setInterval(() => { setTime(time + 1); }, 1000); return () => { window.clearInterval(timer); }; }, []); return ( <div>Seconds: {time}</div> ); } ReactDOM.render(<Clock />, document.querySelector('#app')); <script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script> <script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script> <div id="app"></div>


当前回答

function Clock() {
  const [time, setTime] = React.useState(0);
  React.useEffect(() => {
    const timer = window.setInterval(() => {
      setTime(time => time + 1);// **set callback function here** 
    }, 1000);
    return () => {
      window.clearInterval(timer);
    };
  }, []);

  return (
    <div>Seconds: {time}</div>
  );
}

ReactDOM.render(<Clock />, document.querySelector('#app'));

其他回答

当时间改变时告诉React重新渲染。选择退出

function Clock() { const [time, setTime] = React.useState(0); React.useEffect(() => { const timer = window.setInterval(() => { setTime(time + 1); }, 1000); return () => { window.clearInterval(timer); }; }, [time]); return ( <div>Seconds: {time}</div> ); } ReactDOM.render(<Clock />, document.querySelector('#app')); <script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script> <script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script> <div id="app"></div>

我从这个博客上抄了代码。所有功劳归于船主。https://overreacted.io/making-setinterval-declarative-with-react-hooks/

唯一的事情是,我把这个React代码改编为React Native代码,所以如果你是一个React Native编码器,只要复制这个,并适应你想要的。很容易适应吧!

import React, {useState, useEffect, useRef} from "react";
import {Text} from 'react-native';

function Counter() {

    function useInterval(callback, delay) {
        const savedCallback = useRef();
      
        // Remember the latest function.
        useEffect(() => {
          savedCallback.current = callback;
        }, [callback]);
      
        // Set up the interval.
        useEffect(() => {
          function tick() {
            savedCallback.current();
          }
          if (delay !== null) {
            let id = setInterval(tick, delay);
            return () => clearInterval(id);
          }
        }, [delay]);
      }

    const [count, setCount] = useState(0);

  useInterval(() => {
    // Your custom logic here
    setCount(count + 1);
  }, 1000);
  return <Text>{count}</Text>;
}

export default Counter;

另一种解决方案是使用useReducer,因为它总是被传递当前状态。

function Clock() { const [time, dispatch] = React.useReducer((state = 0, action) => { if (action.type === 'add') return state + 1 return state }); React.useEffect(() => { const timer = window.setInterval(() => { dispatch({ type: 'add' }); }, 1000); return () => { window.clearInterval(timer); }; }, []); return ( <div>Seconds: {time}</div> ); } ReactDOM.render(<Clock />, document.querySelector('#app')); <script src="https://unpkg.com/react@16.7.0-alpha.0/umd/react.development.js"></script> <script src="https://unpkg.com/react-dom@16.7.0-alpha.0/umd/react-dom.development.js"></script> <div id="app"></div>

按照下面的操作,它可以正常工作。

const [count , setCount] = useState(0);

async function increment(count,value) {
    await setCount(count => count + 1);
  }

//call increment function
increment(count);
const [seconds, setSeconds] = useState(0);
  useEffect(() => {
    const interval = setInterval(() => {
      setSeconds((seconds) => {
        if (seconds === 5) {
          setSeconds(0);
          return clearInterval(interval);
        }
        return (seconds += 1);
      });
    }, 1000);
  }, []);

注意:这将有助于使用useState钩子更新和重置计数器。5秒后秒停止。因为首先改变setSecond值,然后在setInterval内用更新的秒停止计时器。as useEffect运行一次。