React 应用程序中的 setInterval

问题描述

我对 React 还是比较陌生，但我一直在慢慢磨合，并且遇到了一些我一直在坚持的事情.

I'm still fairly new at React, but I've been grinding along slowly and I've encountered something I'm stuck on.

我正在尝试在 React 中构建一个计时器"组件，老实说我不知道​​我这样做是否正确(或有效).在下面的代码中，我将状态设置为返回一个对象 { currentCount: 10 } 并且一直在玩弄 componentDidMount、componentWillUnmount 和 render 并且我只能让状态从 10 到 9倒计时".

I am trying to build a "timer" component in React, and to be honest I don't know if I'm doing this right (or efficiently). In my code below, I set the state to return an object { currentCount: 10 } and have been toying with componentDidMount, componentWillUnmount, and render and I can only get the state to "count down" from 10 to 9.

由两部分组成的问题:我做错了什么?而且，有没有更有效的方法来使用 setTimeout(而不是使用 componentDidMount & componentWillUnmount)?

Two-part question: What am I getting wrong? And, is there a more efficient way of going about using setTimeout (rather than using componentDidMount & componentWillUnmount)?

提前致谢.

import React from 'react';

var Clock = React.createClass({

  getInitialState: function() {
    return { currentCount: 10 };
  },

  componentDidMount: function() {
    this.countdown = setInterval(this.timer, 1000);
  },

  componentWillUnmount: function() {
    clearInterval(this.countdown);
  },

  timer: function() {
    this.setState({ currentCount: 10 });
  },

  render: function() {
    var displayCount = this.state.currentCount--;
    return (
      <section>
        {displayCount}
      </section>
    );
  }

});

module.exports = Clock;

推荐答案

我发现您的代码有 4 个问题:

I see 4 issues with your code:

• 在您的计时器方法中，您始终将当前计数设置为 10
• 您尝试更新渲染方法中的状态
• 您没有使用 setState 方法来实际更改状态
• 您没有在状态中存储您的 intervalId

让我们尝试解决这个问题:

Let's try to fix that:

componentDidMount: function() {
   var intervalId = setInterval(this.timer, 1000);
   // store intervalId in the state so it can be accessed later:
   this.setState({intervalId: intervalId});
},

componentWillUnmount: function() {
   // use intervalId from the state to clear the interval
   clearInterval(this.state.intervalId);
},

timer: function() {
   // setState method is used to update the state
   this.setState({ currentCount: this.state.currentCount -1 });
},

render: function() {
    // You do not need to decrease the value here
    return (
      <section>
       {this.state.currentCount}
      </section>
    );
}

这将导致计时器从 10 减少到 -N.如果你想让计时器减少到 0，你可以使用稍微修改的版本:

This would result in a timer that decreases from 10 to -N. If you want timer that decreases to 0, you can use slightly modified version:

timer: function() {
   var newCount = this.state.currentCount - 1;
   if(newCount >= 0) {
       this.setState({ currentCount: newCount });
   } else {
       clearInterval(this.state.intervalId);
   }
},

这篇关于React 应用程序中的 setInterval的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！