元素类型无效：应为字符串或类/函数（用于复合组件）但得到：对象

Question

我正在做一些 React.js 教程，对此我还很陌生。我在dashboard.js中有这段代码

import React from 'react';
import NewChatComponent from '../newChat/newChat';
import ChatListComponent from '../chatList/chatList';
import ChatViewComponent from '../chatView/chatView';
import ChatTextBoxComponent from '../chatTextBox/chatTextBox';
import styles from './styles';
import { Button, withStyles } from '@material-ui/core';
const firebase = require("firebase");

class DashboardComponent extends React.Component {

  constructor() {
    super();
    this.state = {
      selectedChat: null,
      newChatFormVisible: false,
      email: null,
      friends: [],
      chats: []
    };
  }

  render() {

    const { classes } = this.props;

    if(this.state.email) {
      return(
        <div className='dashboard-container' id='dashboard-container'>
          <ChatListComponent history={this.props.history} 
            userEmail={this.state.email} 
            selectChatFn={this.selectChat} 
            chats={this.state.chats} 
            selectedChatIndex={this.state.selectedChat}
            newChatBtnFn={this.newChatBtnClicked}>
          </ChatListComponent>
          {
            this.state.newChatFormVisible ? null : <ChatViewComponent 
              user={this.state.email} 
              chat={this.state.chats[this.state.selectedChat]}>
            </ChatViewComponent>
          }
          { 
            this.state.selectedChat !== null && !this.state.newChatFormVisible ? <ChatTextBoxComponent userClickedInputFn={this.messageRead} submitMessageFn={this.submitMessage}></ChatTextBoxComponent> : null 
          }
          {
            this.state.newChatFormVisible ? <NewChatComponent goToChatFn={this.goToChat} newChatSubmitFn={this.newChatSubmit}></NewChatComponent> : null
          }
          <Button onClick={this.signOut} className={classes.signOutBtn}>Sign Out</Button>
        </div>
      );
    } else {
      return(<div>LOADING....</div>);
    }
  }

  signOut = () => firebase.auth().signOut();

  submitMessage = (msg) => {
    const docKey = this.buildDocKey(this.state.chats[this.state.selectedChat]
      .users
      .filter(_usr => _usr !== this.state.email)[0])
    firebase
      .firestore()
      .collection('chats')
      .doc(docKey)
      .update({
        messages: firebase.firestore.FieldValue.arrayUnion({
          sender: this.state.email,
          message: msg,
          timestamp: Date.now()
        }),
        receiverHasRead: false
      });
  }

  // Always in alphabetical order:
  // 'user1:user2'
  buildDocKey = (friend) => [this.state.email, friend].sort().join(':');

  newChatBtnClicked = () => this.setState({ newChatFormVisible: true, selectedChat: null });

  newChatSubmit = async (chatObj) => {
    const docKey = this.buildDocKey(chatObj.sendTo);
    await 
      firebase
        .firestore()
        .collection('chats')
        .doc(docKey)
        .set({
          messages: [{
            message: chatObj.message,
            sender: this.state.email
          }],
          users: [this.state.email, chatObj.sendTo],
          receiverHasRead: false
        })
    this.setState({ newChatFormVisible: false });
    this.selectChat(this.state.chats.length - 1);
  }

  selectChat = async (chatIndex) => {
    await this.setState({ selectedChat: chatIndex, newChatFormVisible: false });
    this.messageRead();
  }

  goToChat = async (docKey, msg) => {
    const usersInChat = docKey.split(':');
    const chat = this.state.chats.find(_chat => usersInChat.every(_user => _chat.users.includes(_user)));
    this.setState({ newChatFormVisible: false });
    await this.selectChat(this.state.chats.indexOf(chat));
    this.submitMessage(msg);
  }

  // Chat index could be different than the one we are currently on in the case
  // that we are calling this function from within a loop such as the chatList.
  // So we will set a default value and can overwrite it when necessary.
  messageRead = () => {
    const chatIndex = this.state.selectedChat;
    const docKey = this.buildDocKey(this.state.chats[chatIndex].users.filter(_usr => _usr !== this.state.email)[0]);
    if(this.clickedMessageWhereNotSender(chatIndex)) {
      firebase
        .firestore()
        .collection('chats')
        .doc(docKey)
        .update({ receiverHasRead: true });
    } else {
      console.log('Clicked message where the user was the sender');
    }
  }

  clickedMessageWhereNotSender = (chatIndex) => this.state.chats[chatIndex].messages[this.state.chats[chatIndex].messages.length - 1].sender !== this.state.email;

  componentWillMount = () => {
      firebase.auth().onAuthStateChanged(async _usr => {
        if(!_usr)
          this.props.history.push('/login');
        else {
          await firebase
            .firestore()
            .collection('chats')
            .where('users', 'array-contains', _usr.email)
            .onSnapshot(async res => {
              const chats = res.docs.map(_doc => _doc.data());
              await this.setState({
                email: _usr.email,
                chats: chats,
                friends: []
              });
            })
        }
    });
  }
}

export default withStyles(styles)(DashboardComponent);

有问题的代码行是这一行：-

newChatBtnClicked = () => this.setState({ newChatFormVisible: true, selectedChat: null });

如果我设置 newChatFormbVisible: false，我不会收到错误，但是将其设置为 true，会失败并出现以下错误：-

index.js:1375 警告：React.createElement：类型无效 -- 期望一个字符串（对于内置组件）或一个类/函数（对于 复合组件）但得到：对象。您可能忘记导出 你的组件来自它定义的文件，或者你可能混合了 设置默认和命名导入。

在 dashboard.js:47 检查您的代码。 在 DashboardComponent 中（由 WithStyles(DashboardComponent) 创建） 在 WithStyles(DashboardComponent) 中（由 Context.Consumer 创建） 在路线中（在 src/index.js:28） 在 div 中（在 src/index.js:25） 在路由器中（由 BrowserRouter 创建） 在 BrowserRouter（位于 src/index.js:24）控制台中。 @index.js:1375 警告WithoutStack @react.development.js:188 警告@ react.development.js:623 createElementWithValidation @ react.development.js:1785 渲染@dashboard.js:44 finishClassComponent @ react-dom.development.js:15319 updateClassComponent @ react-dom.development.js:15274 beginWork @ react-dom.development.js:16262 performUnitOfWork @ react-dom.development.js:20279 workLoop @ react-dom.development.js:20320 渲染根@ react-dom.development.js:20400 performWorkOnRoot @ react-dom.development.js:21357 performWork @ react-dom.development.js:21267 performSyncWork @ react-dom.development.js:21241 interactiveUpdates$1 @ react-dom.development.js:21526 交互更新@ react-dom.development.js:2268 dispatchInteractiveEvent @ react-dom.development.js:5085 react-dom.development.js:57 未捕获 Invariant Violation：元素类型无效：需要一个字符串（对于 内置组件）或类/函数（用于复合组件） 但得到：对象。您可能忘记从 它在其中定义的文件，或者您可能混淆了默认值和命名 进口。

Answer 1

我们在 cmets 部分与 @Johann 讨论后，我才写下这个答案。因此，如果他们遇到相同类型的错误，其他人更容易看到

好的，我不确定，但您可以尝试使用带有自结束标签的组件，例如<ChatViewComponent />