The issue is that upon each render cycle, markup is redefined. React uses shallow object comparison to determine if a value updated or not. Each render cycle markup has a different reference. You can use useCallback to memoize the function though so the reference is stable. Do you have the react hook rules enabled for … Read more
React performs the cleanup when the component unmounts. I’m not sure where you read this but this statement is incorrect. React performs the cleanup when the dependencies to that hook changes and the effect hook needs to run again with new values. This behaviour is intentional to maintain the reactivity of the view to changing … Read more
Below solution worked for me: import React, { useEffect } from “react”; import { useIsFocused } from “@react-navigation/native”; const ExampleScreen = (props) => { const isFocused = useIsFocused(); useEffect(() => { console.log(“called”); // Call only when screen open or when back on screen if(isFocused){ getInitialData(); } }, [props, isFocused]); const getInitialData = async () => … Read more
It’s not quite the same. Giving it an empty array acts like componentDidMount as in, it only runs once. Giving it no second argument acts as both componentDidMount and componentDidUpdate, as in it runs first on mount and then on every re-render. Giving it an array as second argument with any value inside, eg , … Read more
The pattern that you need to follow depends on your use case. First: You might have a situation where you need to add event listener during the initial mount and clean them up at unmount and another case where a particular listener needs to be cleaned up and re-added on a prop change. In such … Read more
If you only want to run the function given to useEffect after the initial render, you can give it an empty array as second argument. function MyComponent() { useEffect(() => { loadDataOnlyOnce(); }, []); return <div> {/* … */} </div>; }
If you aren’t using fetchBusinesses method anywhere apart from the effect, you could simply move it into the effect and avoid the warning useEffect(() => { const fetchBusinesses = () => { return fetch(“theURL”, {method: “GET”} ) .then(res => normalizeResponseErrors(res)) .then(res => { return res.json(); }) .then(rcvdBusinesses => { // some stuff }) .catch(err => … Read more