当父组件的 state 更改时，子组件不会重新渲染

Question

I have the following issue: I have an Component that renders other components in it. One of this component gets state variables of my parent component as parameter and are using them actively, but they don't rerender when the state of the parent component changes. Another problem that I am facing is that I have an additional item in my list that navigates that is activated when the user has a special roleID. The changing of the state works completely fine, but in this situation the additional item only gets visible after I changed the path param of my url.

parent component:

import React, { useEffect, useState } from 'react';
import {Row, Col} from 'react-bootstrap';
import 'bootstrap/dist/css/bootstrap.min.css';
import '../../App.css';
import ProfileSettings from './profileSettings';
import SettingsChooser from './settingsChooser';
// import SettingRoutings from '../settingRoutings';
import {BrowserRouter as Router, useHistory, useLocation, useParams} from 'react-router-dom';
// import Routings from '../Routings.js';
import UserRequests from './userRequests';
import useAuth from '../../API/useAuthentification';
import { CONTROLLERS, useBackend } from '../../hooks/useBackend';

function UserSettings({user}) {

    const {title: path} = useParams();
    const [acst, setAcst] = useState(localStorage.accessToken);
    const [rft, setRft] = useState(localStorage.refreshToken);
    const history = useHistory();
    const [items, setItems] = useState(['Profile', 'Requests','Log Out', 'Delete Account']);
    const [authError, setAuthError] = useState(false);
    const [userValues, authentificate] = useBackend(authError, setAuthError, user);
    const [component, setComponent] = useState(<></>);
    const [defaultItem, setDefaultItem] = useState(0);
    

    useEffect(() => {
        console.log('render');
        authentificate(CONTROLLERS.USERS.getUserByAccessToken());
    }, [acst, rft]);

    window.addEventListener('storage', () => localStorage.accessToken !== acst ? setAcst(localStorage.accessToken) : '');
    window.addEventListener('storage', () => localStorage.refreshToken !== rft ? setRft(localStorage.refreshToken) : '');

    useEffect(() => {
        if(userValues?.roleID === 1) {
            items.splice(0, 0, 'Admin Panel');
            setItems(items);
        }
        console.log(items);
    }, [userValues]);

    useEffect(() => {
        // if(path==='logout') setDefaultItem(2);
        // else if(path==='deleteAccount') setDefaultItem(3);
        // else if(path==='requests') setDefaultItem(1);
    }, [])

    const clearTokens = () => {
        localStorage.accessToken = undefined;
        localStorage.refreshToken = undefined;
    }
    useEffect(() => {
        console.log(path);
        if(path ==='logout' && !authError) {
            setDefaultItem(2);
            clearTokens();
        }
        else if(path === 'deleteaccount') {
            setDefaultItem(3);
            if(userValues?.userID && !authError) {
             authentificate(CONTROLLERS.USERS.delete(userValues.userID));
             }
            clearTokens();
            history.push('/movies/pages/1');
        }
        else if(path==='requests') {
            setDefaultItem(1);
            setComponent(<UserRequests user={userValues} setAuthError={setAuthError} authError={authError}/>);
        } else {
            setComponent(<ProfileSettings user={userValues} setAuthError={setAuthError} authError={authError}/>);
        }
    }, [path]);

    useEffect(() => {
        console.log(defaultItem);
    }, [defaultItem])
    

 

    return (
            <div >
            <Row className="">
            <Col className="formsettings2"   md={ {span: 3, offset: 1}}>
                <SettingsChooser  items={items} headline={'Your Details'} defaultpath='userSettings' defaultactive={defaultItem} />
            </Col>
           <Col  className="ml-5 formsettings2"md={ {span: 6}}>
                     {authError ? <p>No Access, please Login first</p> : component}
            </Col>
            </Row>
            </div>
    );
}

export default UserSettings;

Child component (settingsChooser):

import React, {useEffect, useState} from 'react';
import {Card, Form, Button, Nav, Col} from 'react-bootstrap';
import 'bootstrap/dist/css/bootstrap.min.css';
import { LinkContainer } from 'react-router-bootstrap';
import '../../App.css'

function SettingsChooser({items, headline, defaultpath, defaultactive}) {

    const [selected, setSelected] = useState(defaultactive);
   

    const handleClick = (e, key) => {
        setSelected(key);
    }

    useEffect(() => console.log("rerender"), [items, defaultactive]);

    useEffect(() => {
        setSelected(defaultactive);
    }, [])

    return(
        <>
        <Card className="shadow-sm">
            <Card.Header className="bg-white h6 ">{headline}</Card.Header>
        {items.map((item, idx) =>{
            return(
              <LinkContainer to={`/${defaultpath}/${(item.replace(/\s/g,'').toLowerCase())}`}><Nav.Link onClick={(e) => handleClick(this, idx)}  className={'text-decoration-none text-secondary item-text ' + (selected === idx? 'active-item' : 'item')}>{item}</Nav.Link></LinkContainer>
            );           
        })}
        </Card>
        </>
    );
}

export default SettingsChooser;

Answer 1

Firstly, in your parent component when you do

setItems(items)

you are not actually modifying the state, since items already is stored in the state. React will check the value you pass, and not cause a re-render if the value is already stored in the state. When you modify your array with splice, it is still the "same" array, just different contents.

One way around this is to do setItems([...items]) , which will call setItems with a new array, containing the same items.

Secondly, in your child class, the following currently has no effect:

useEffect(() => {
    setSelected(defaultactive);
}, [])

Since the dependency array is empty, it will only be called on the first render. If you want it to be called any time defaultactive changes, you need to do this instead:

useEffect(() => {
    setSelected(defaultactive);
}, [defaultactive])