javascript - React JS 上的 Firebase Firestore 双循环数据

Question

我有这样的代码 模型.js

    import firebase from '../config/Firebase'
    class Dashboard {
        GetAllBlog() {
            return firebase.collection('blogs').get()
        }
    }
    export default new Dashboard()

然后，我将模型返回到 home.js

import React from 'react';
import Index from './components/index'
import CardOverview from './components/CardOverview'

import PropTypes from 'prop-types';
import { withStyles } from '@material-ui/core/styles';
import Container from '@material-ui/core/Container'
import Paper from '@material-ui/core/Paper'
import Grid from '@material-ui/core/Grid'
import Typography from '@material-ui/core/Typography';
import DashboardService from '../services/dashboard'
const styles = theme => ({
  root: {
    padding: theme.spacing(3, 2),
  },
  row: {
    padding: theme.spacing(3, 2),
  }
});

class Home extends React.Component {
  state = {
    blogs: []
  }

  componentDidMount() {
    DashboardService.GetAllBlog()
      .then(snapshot => {
        this.setState({
          blogs: snapshot
        })
      })
      .catch(err => {
        console.log('Error getting documents', err);
      });
  }
  render() {
    const { classes } = this.props
    const {
      blogs
    } = this.state

    blogs.forEach(element => {
      console.log("blogs", element.data().title)

    });
    return (
.......

但是当像这样使用 foreach 时我得到了双倍

.,

其实我有这样的数据(两条数据)

我看看如何通过将所有快照转换为数组来使其变得简单，(我可以从 firebase 创建连接数组)，但我很困惑，为什么这个双循环，但它循环了 2 次，但一次，它是基于循环的按长度排列

Answer 1

这是因为状态改变了2次，那么每次改变状态都会执行渲染