I've been learning react over the last few days and for the most part it makes sense, however there is one thing that is stumping me.
If I have
- A Parent element with some state variables and a callback method
- A child element that takes a callback method as a prop
- The callback method relies on some piece of state that is in the parent element
- I don't want to re-create the view object every time any state changes
Every time I try to do this, it seems like the child element is calling some older version of the parent element (presumably the instance of the parent that actually created the child) instead of the current version.
I'm getting the feeling that what I want is just wrong on a fundamental level and isnt The React Way
The reason that I am trying to do this is that my main parent contains 17 divs, each of which represent a key on a musical instrument, and each of which contains at least 20-30 divs. The lowest div (of which there are at least a few hundred) has an onClick event that I want to modify the functionality of based on whether modifier keys are held down (shift, control etc).
Currently I have Raised the state of the shiftPressed to be on the single parent element then passed down the value of that into each child through props, however re-rendering hundreds of divs whenever a user pushes shift takes quite a while.
I've made a code sandbox to show the current problem sandbox
Sandbox code:
import "./styles.css";
import { useState, useEffect, useRef } from "react";
export default function App() {
//Our state holding data
const [state, setState] = useState(false);
//Our state holding the view
const [view, setView] = useState(<div></div>);
const printState = useRef(null);
//Component did mount hook
useEffect(() => {
reGenerate();
}, []);
//state update hook
useEffect(() => {
printState.current();
}, [state]);
//function to flip the state
const flipState = () => {
setState(!state);
};
//The method that updates the view
//(The idea being that I don't want to update the view on every state change)
const reGenerate = () => {
setView(
<>
<p>
State: {state && "true"} {state || "false"}
</p>
<Child callback={printState} />
</>
);
};
//Method for validation
printState.current = () => {
console.log("Printed state: " + state);
};
return (
<div className="App">
<h1>Parent-child-prop-problem (prop-lem)</h1>
<ol>
<li>click "force regeneration"</li>
<li>
click "flip state" and the value of state after the flip will be
printed in console, but it won't show up on the HTML element
</li>
<li>
Click "print state (from child)" and observe that the console is
printing the old version of the state
</li>
</ol>
<button onClick={flipState}>Flip State</button>
<button onClick={reGenerate}>Force Regeneration</button>
{view}
</div>
);
}
function Child(props) {
return (
<div>
<button onClick={props.callback.current}>Print State (from child)</button>
</div>
);
}