Erkundung der Kontext-API-Anwendung

Question

Ich habe viele Methoden ausprobiert. Nachdem ich viele der oben genannten Lösungen gelesen habe, konnte ich dieses Problem immer noch nicht lösen. Kann mir jemand helfen, Kontext in meinem Projekt zu verwenden?

SearchContext.jsx

import { createContext } from 'react';

const SearchContext = createContext();

export default SearchContext;

Search.jsx

import * as React from 'react';
import { useState, useContext } from 'react';
import Paper from '@mui/material/Paper';
import AccountCircleIcon from '@mui/icons-material/AccountCircle';
import SearchIcon from '@mui/icons-material/Search';
import { Box, IconButton, InputBase } from '@mui/material';
import SearchContext from '../Context/SearchContext';

export default function Search() {
    const [searchQuery, setSearchQuery] = useState('');
    const handleSubmit = (event) => {
        event.preventDefault();
    };

    const handleInputChange = (event) => {
        setSearchQuery(event.target.value);
    };
    return (
        <SearchContext.Provider value={searchQuery} >
            <Box display='flex' alignItems='center' justifyContent='center' paddingTop='20px'>
                <Paper component="form" sx={{ p: '2px 10px', display: 'flex', width: '50%' }} onSubmit={handleSubmit}>
                    <IconButton type="button" sx={{ p: '10px' }} aria-label="search">
                        <AccountCircleIcon fontSize='large' />
                    </IconButton>
                    <InputBase
                        sx={{ ml: 1, flex: 1 }}
                        placeholder="Search User"
                        inputProps={{ 'aria-label': 'search user' }}
                        onChange={handleInputChange}
                    />
                    <IconButton type="submit" sx={{ p: '10px' }} aria-label="search">
                        <SearchIcon fontSize='large' />
                    </IconButton>
                </Paper>
            </Box>
        </SearchContext.Provider>
    );
}

Das verwende ich. ist es richtig ? Ich habe es später hier verwendet

import React, { useContext, useEffect, useState } from 'react';
import { ApiService } from '../../API/ApiService';
import SearchContext from '../../Context/SearchContext';


function NumberOfContestParticipated({ handle }) {
    const [contestCount, setContestCount] = useState(null);
    const searchQuery = useContext(SearchContext);
    console.log(searchQuery);
    useEffect(() => {
        const fetchData = async () => {
            const ratingUrl = `https://codeforces.com/api/user.rating?handle=${handle}`;
            const ratingData = await ApiService(ratingUrl);

            if (ratingData && ratingData.status === 'OK') {
                setContestCount(ratingData.result.length);
            } else {
                setContestCount(0);
            }
        };

        fetchData();
    }, [handle]);

    return (
        <div>
            {contestCount !== null ? (
                <p>Number of contests participated by {handle}: {contestCount}</p>
            ) : (
                <p>Loading...</p>
            )}
        </div>
    );
}

export default NumberOfContestParticipated;

Aber wenn ich searchQuery protokolliere, gibt es einen undefinierten Wert. Was habe ich falsch gemacht?

Index.js

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import SearchContext from './Context/SearchContext';

ReactDOM.render(
  <SearchContext.Provider>
    <App />
  </SearchContext.Provider>
  , document.getElementById('root')
);

Answer 1

我认为您的问题是 NumberOfContestParticipated 组件不是 Provider 组件的子组件，因此当状态更改时上下文仍然未定义。另外，我觉得很奇怪，您将应用程序包装在提供程序中两次，如果您包装整个 App 组件，则不需要这样做。

查看这篇文章，了解有关如何操作的更多信息使用上下文。