我想用React在一个表中显示一些记录,但我得到了这个错误:

无效的钩子调用。类的主体内部只能调用钩子 功能组件。这可能发生在以下情况之一 原因: React和渲染器的版本可能不匹配(比如React DOM) 你可能违反了胡克斯的规矩 你可能在同一个应用程序中有多个React副本,请参阅有关如何调试和调试的提示 解决这个问题。

import React, {
  Component
} from 'react';
import {
  makeStyles
} from '@material-ui/core/styles';
import Table from '@material-ui/core/Table';
import TableBody from '@material-ui/core/TableBody';
import TableCell from '@material-ui/core/TableCell';
import TableHead from '@material-ui/core/TableHead';
import TableRow from '@material-ui/core/TableRow';
import Paper from '@material-ui/core/Paper';

const useStyles = makeStyles(theme => ({
  root: {
    width: '100%',
    marginTop: theme.spacing(3),
    overflowX: 'auto',
  },
  table: {
    minWidth: 650,
  },
}));

class allowance extends Component {
  constructor() {
    super();
    this.state = {
      allowances: [],
    };

  }

  componentWillMount() {
    fetch('http://127.0.0.1:8000/allowances')
      .then(data => {

        return data.json();

      }).then(data => {

        this.setState({
          allowances: data
        });

        console.log("allowance state", this.state.allowances);
      })

  }



  render() {
    const classes = useStyles();
    return ( <
      Paper className = {
        classes.root
      } >
      <
      Table className = {
        classes.table
      } >
      <
      TableHead >
      <
      TableRow >
      <
      TableCell > Allow ID < /TableCell> <
      TableCell align = "right" > Description < /TableCell> <
      TableCell align = "right" > Allow Amount < /TableCell> <
      TableCell align = "right" > AllowType < /TableCell>

      <
      /TableRow> <
      /TableHead> <
      TableBody > {
        this.state.allowances.map(row => ( <
          TableRow key = {
            row.id
          } >
          <
          TableCell component = "th"
          scope = "row" > {
            row.AllowID
          } <
          /TableCell> <
          TableCell align = "right" > {
            row.AllowDesc
          } < /TableCell> <
          TableCell align = "right" > {
            row.AllowAmt
          } < /TableCell> <
          TableCell align = "right" > {
            row.AllowType
          } < /TableCell>                     <
          /TableRow>
        ))
      } <
      /TableBody> <
      /Table> <
      /Paper>
    );
  }

}

export default allowance;

当前回答

您可以查看您的路线。如果你在Route(<Route path="/testpath" render = {(props)=><Test{…Props} />} />) 你在一个箭头函数中调用了你的组件,给它传递了合适的道具。

其他回答

我刚刚开始使用钩子,当我在函数中调用useEffect时,我得到了上面的警告:

然后我必须将useEffect移到函数之外,如下所示:

 const onChangeRetypePassword = async value => {
  await setRePassword(value);
//previously useEffect was here

  };
//useEffect outside of func 

 useEffect(() => {
  if (password !== rePassword) {
  setPasswdMismatch(true);

     } 
  else{
    setPasswdMismatch(false);
 }
}, [rePassword]);

希望对大家有所帮助!

对我来说,这个问题是由webpack设置解决引起的。Symlinks (https://webpack.js.org/configuration/resolve/#resolvesymlinks),设置为false:

  resolve: {
    symlinks: false,

因此,从另一个包到React的符号链接无法解析,并导致无效钩子调用错误。

将它设置为true或简单地省略它(显然它默认为true)解决了问题:

  resolve: {
    symlinks: true,

你可以通过调用一个箭头函数来返回它的React来使用“export default”。通过将MaterialUI类对象道具传递给组件,这些道具将在Component render()中使用。

class AllowanceClass extends Component{
    ...
    render() {
        const classes = this.props.classes;
        ...
    }
}

export default () => {
    const classes = useStyles();
    return (
        <AllowanceClass classes={classes} />
    )
}

在我的例子中,这只是我的App.js上的这一行代码,导致了这个问题,让我在调试上浪费了10个小时。React Native和Expo不能告诉我这一点。我在StackOverflow和github上做了所有的事情,甚至在react页面上应该解决这个问题,但问题仍然存在。为了找到罪魁祸首,我不得不一点一点地把我的代码拆开

 **const window = useWindowDimensions();**

它是这样摆放的:

import * as React from 'react';
import { Text, View, StyleSheet, ImageBackground, StatusBar, Image, Alert, SafeAreaView, Button, TouchableOpacity, useWindowDimensions } from 'react-native';
import Constants from 'expo-constants';

import Whooksplashscreen11 from './Page1';
import Screen1 from './LoginPage';
import Loginscreen from './Login';
import RegisterScreen1 from './register1';
import RegisterScreen2 from './register2-verifnum';
import RegisterScreen3 from './register3';
import RegisterScreen4 from './register4';
import RegisterScreen5 from './register5';
import RegisterScreen6 from './register6';
import BouncyCheckbox from "react-native-bouncy-checkbox";
import LocationPermission from './LocationPermission.js'
import Selfieverif1 from './selfieverif1'
import Selfieverif2 from './selfieverif2'
import AddPhotos from './addphotos'


// You can import from local files
import { useFonts } from 'expo-font';

// or any pure javascript modules available in npm

import { NavigationContainer } from '@react-navigation/native';
import { createNativeStackNavigator } from '@react-navigation/native-stack';


//FontAwesome
import { library } from '@fortawesome/fontawesome-svg-core'
import { fab, } from '@fortawesome/free-brands-svg-icons'
import { faCheckSquare, faCoffee, faFilter, faSearch,  } from '@fortawesome/free-solid-svg-icons'
import { FontAwesomeIcon } from '@fortawesome/react-native-fontawesome'
import Icon  from "react-native-vector-icons/FontAwesome5";

import MyTabs from './swipepage'

library.add(fab, faCheckSquare, faCoffee, faFilter, faSearch,);


const window = useWindowDimensions();
const Stack = createNativeStackNavigator();

function App() {
  return ( ....
)}

在我的情况下,我试图在窗户上使用mdbreact。虽然它安装了,但我得到了上述错误。我不得不重新安装,一切正常。我曾经在antd图书馆遇到过一次