javascript - react 状态值不更新

Question

我想通过传递名为 topicsVisited 的变量的值来更新 topicsVisited 状态的值。但是，它没有更新值。当用户访问主题页面的末尾时，它应该将 topicID 值推送到数组，该数组值将存储在本地存储中并传输到状态。

import {React, ReactDOM} from '../../../../build/react';

import SelectedTopicPageMarkup from './selected-topic-page-markup.jsx';
import NextPrevBtn from './next-prev-btn.jsx';

export default class SelectedTopicPage extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      topicPageNo: 0,
      total_selected_topic_pages: 1,
      topicsVisited: []
    };
  };
  navigateBack(topicPageNo) {
    if (this.state.topicPageNo > 0) {
      topicPageNo = this.state.topicPageNo - 1;
    } else {
      topicPageNo = 0;
    }
    this.setState({topicPageNo: topicPageNo});
  };
  navigateNext(totalPagesInSelectedTopic) {
    let topicPageNo;
    if (totalPagesInSelectedTopic > this.state.topicPageNo + 1) {
      topicPageNo = this.state.topicPageNo + 1;
    } else if (totalPagesInSelectedTopic == this.state.topicPageNo + 1) {
      let topicsVisited = JSON.parse(localStorage.getItem('topicsVisited')) || [];
      topicsVisited.push(parseInt(this.props.topicsID));
      localStorage.setItem("topicsVisited", JSON.stringify(topicsVisited));
      this.setState({topicsVisited: topicsVisited});
      console.log(this.state.topicsVisited);
      this.props.setTopicClicked(false);
    } else {
      topicPageNo = this.state.topicPageNo;
    }
    this.setState({topicPageNo: topicPageNo});
  };

  render() {
    let topicsID = this.props.topicsID;
    let topicPageNo = this.state.topicPageNo;
    return (
      <div>
        {this.props.topicPageData.filter(function(topicPage) {
          // if condition is true, item is not filtered out
          return topicPage.topic_no === topicsID;
        }).map(function(topicPage) {
          let totalPagesInSelectedTopic = topicPage.topic_pages.length;
          return (
            <div>
              <div>
                <SelectedTopicPageMarkup headline={topicPage.topic_pages[0].headline} key={topicPage.topic_no}>
                  {topicPage.topic_pages[topicPageNo].description}
                </SelectedTopicPageMarkup>
              </div>
              <div>
                <NextPrevBtn moveNext={this.navigateNext.bind(this, totalPagesInSelectedTopic)} key={topicPage.topic_no} moveBack={this.navigateBack.bind(this, topicPageNo)}/>
              </div>
            </div>
          );
        }.bind(this))}
      </div>
    );
  };
};

Answer 1

setState文档讨论了两件重要的事情:

There is no guarantee of synchronous operation of calls to setState and calls may be batched for performance gains.

和

The second (optional) parameter is a callback function that will be executed once setState is completed and the component is re-rendered.

您可能希望合并两个 setState 调用或使用回调来完成您希望在状态更改后完成的工作。

回调看起来像这样:

this.setState({topicsVisited: topicsVisited}, function() {
    console.log(this.state.topicsVisited);
    this.props.setTopicClicked(false);
}.bind(this));