如何通过反应上下文保持价值？

Question

Here are 3 basic components searchBar which refers to the search bar form and, the searchPage component which displays the search results , and of course, the app component which contains them all .

mechanism:

1. the user submits an input in the searchBar component , the handleSubmit function gets fired, which changes the state of setSearchedProducts to the input value, by useContext AND getting pushed to the ("/SearchPage") by history.push() .

 import {useState, useContext } from "react"; import { useHistory } from "react-router-dom"; import { LocaleContext } from "../../../LocaleContext"; const SearchBar = () => { const history = useHistory(); const {setSearchedTerm} = useContext(LocaleContext); const handleSubmit = (SearchTerm) => { setSearchedProducts(SearchTerm) history.push("/SearchPage"); } return ( <form> <input onSubmit={(e) => handleSubmit(e.target.value)}> </input> <button type="submit">Submit</button> </form> ) } export default SearchBar

2. the value gets sent to the app component by react context and the state gets set to the value while still pushing to the ("/searchPage").

 import { useState, useMemo } from "react"; import { searchBar, searchPage } from "./components"; import { BrowserRouter as Router, Switch, Route } from "react-router-dom"; import {LocaleContext} from "./LocaleContext" const App = () => { const [searchedTerm, setSearchedTerm] = useState(""); const providerValue = useMemo(() => ({searchedTerm, setSearchedTerm}), [searchedTerm, setSearchedTerm]) return ( <Router> <LocaleContext.Provider value={providerValue}> <searchBar /> <Switch> <Route exact path="/SearchPage"> <SearchPage /> </Route> </Switch> </LocaleContext.Provider> </Router> ); } export default (App);

3. displaying the searchPage component , which gets the state value by using useContext , and with useEffect , the fetchProducts() function gets fired, that fetches a set of products based on the state value.

 import {useState, useEffect, useContext} from 'react'; import { LocaleContext } from "../../LocaleContext"; const SearchPage = ({}) => { const [products, setProducts] = useState([]); const {searchedTerm} = useContext(LocaleContext); const fetchProducts = (term) => { setLoading(true); const url = new URL( "https://example/products" ); let params = { "query": term }; Object.keys(params).forEach(key => url.searchParams.append(key, params[key])); let headers = { "Accept": "application/json", "Content-Type": "application/json", }; fetch(url, { method: "GET", headers: headers, }).then(response => response.json()).then(json => { setProducts(json); }); } useEffect(() => { fetchProducts(searchedProducts) }, []) return ( { products.map(product => ( <div> {product.name} </div> )) } ) } export default SearchPage

Issues:

• when the router changes to the ("/searchPage") component state value get lost, meaning it returns to "" value. ?
• lesser problem, if the user sends an empty string (" "), and the API needs a value or it will give an error, what is the solution to that?
• is there a way of keeping the value after reloading the page?

 import {createContext} from "react"; export const LocaleContext = createContext(null);

this is the localeContext component if needed.

Answer 1

you have to add e.preventDefault() in your onSubmit handler. Otherwise you're getting a page reload which causes a state loss.

Answer 2

I noticed "setSearchedProducts" & "setSearchedTerm" should be the same in your code below. This might be your issue!

 const SearchBar = () => {... const {setSearchedTerm} = useContext(LocaleContext); const handleSubmit = (SearchTerm) => { setSearchedProducts(SearchTerm)... }