警告Reactjs-未定義-有解無憂

我為學校的一個專案作業，但我遇到了一些問題。

所以這是代碼

import React from 'react';
import { AppBar, Container, Toolbar, Typography, MenuItem, Select, makeStyles, createTheme, ThemeProvider } from "@material-ui/core";
import { useNavigate } from "react-router-dom";
import { CryptoState } from '../CryptoContext';

//Creeare Design - Titlu
const useStyles = makeStyles(() => ({
  title: {
    flex:1,
    color: "gold",
    fontFamily: "Montserrat",
    fontWeight: "bold",
    cursor: "pointer",
  }
}))

const Header = () => {

  const classes = useStyles();
  const navigate = useNavigate();
  const {currency,setCurrency} = CryptoState() || {};
  

  console.log(currency);

  // TODO: Gandire sistem reintoarcere pagina principala 
  const handleClick = () => navigate.push('/'); // nu merge - reintoarcere la pagian principala


  // FIXME: Creeare template tem?
  const darkTheme = createTheme({
    palette:{
      primary: {
        main: "#fff",
      },
      type: "dark",
    },
  });

  return (
    <ThemeProvider theme={darkTheme}>
      <AppBar color='transparent' position='static'>
          <Container>
            <Toolbar>
              <Typography onClick={handleClick} 
              className={classes.title} variant='h5'>Crypto Hunter</Typography>
              <Select variant="outlined" style={{
                width:100,
                height:40,
                marginLeft: 15,
              }}
              value={currency} onChange={(e) => setCurrency(e.target.value)}
              >
                <MenuItem value={"RON"}>RON</MenuItem>
                <MenuItem value={"EUR"}>EUR</MenuItem>
                <MenuItem value={"USD"}>USD</MenuItem>
              </Select>
            </Toolbar>
          </Container>
      </AppBar>
      </ThemeProvider>
  )
};

export default Header;

這就是問題所在，我不知道如何解決它們。我想要的是？

圖片在這里

警告 Reactjs - 未定義

請幫我！

如果我使用 RON 或 USD 或 EURO 從選擇中更改，我想 console.log 可以轉到下一步。但她給了我這個錯誤（圖片），我不知道如何解決這個問題'

編輯：

另外，從 CryptoState 我有這個代碼

    const Crypto = createContext();

const CryptoContext = ({children}) => {

 const [currency, setCurrency] = useState("RON");
 const [symbol, setSymbol] = useState("RON");

  useEffect(() => {
      if(currency === "RON") setSymbol("RON");
      else if(currency === "EUR") setSymbol("€");
      else if(currency === "USD") setSymbol("$");
  },[currency]);

return <Crypto.Provider value={{currency,symbol,setCurrency}}>{children}</Crypto.Provider>
};


export default CryptoContext;

export const CryptoState = () => {
    useContext(Crypto);
}

uj5u.com熱心網友回復：

改變那條線

 const {currency,setCurrency} = CryptoState() || {};

至

 const [currency,setCurrency] =useState(CryptoState() || {}) ;

轉載請註明出處，本文鏈接：https://www.uj5u.com/qita/524581.html

標籤：javascript反应

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