How to add "refs" dynamically with react hooks?

Question

So I have an array of data in and I am generating a list of components with that data. I'd like to have a ref on each generated element to calculate the height. I know how to do it with a Class component, but I would like to do it with React Hooks.

Here is an example explaining what I want to do:

import React, {useState, useCallback} from 'react'
const data = [
  {
    text: 'test1'
  },
  {
    text: 'test2'
  }
]
const Component = () => {
  const [height, setHeight] = useState(0);
  const measuredRef = useCallback(node => {
    if (node !== null) {
      setHeight(node.getBoundingClientRect().height);
    }
  }, []);

  return (
    <div>
      {
        data.map((item, index) => 
          <div ref={measuredRef} key={index}>
            {item.text}
          </div>
        )
      }
    </div>
  )
}

Answer 1

Not sure i fully understand your intent, but i think you want something like this:

 const { useState, useRef, createRef, useEffect } = React; const data = [ { text: "test1" }, { text: "test2" } ]; const Component = () => { const [heights, setHeights] = useState([]); const elementsRef = useRef(data.map(() => createRef())); useEffect(() => { const nextHeights = elementsRef.current.map( ref => ref.current.getBoundingClientRect().height ); setHeights(nextHeights); }, []); return ( <div> {data.map((item, index) => ( <div ref={elementsRef.current[index]} key={index} className={`item item-${index}`}> {`${item.text} - height(${heights[index]})`} </div> ))} </div> ); }; const rootElement = document.getElementById("root"); ReactDOM.render(<Component />, rootElement);

 .item { box-sizing: border-box; display: flex; align-items: center; justify-content: center; border: 1px solid #ccc; } .item-0 { height: 25px; } .item-1 { height: 50px; }

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.6/umd/react.production.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.6/umd/react-dom.production.min.js"></script> <div id="root"/>

Answer 2

I created a tiny npm package that exposes a React Hook to handle setting and getting refs dynamically as I often run into the same problem.

npm i use-dynamic-refs

Here's a simple example.

import React, { useEffect } from 'react';
import useDynamicRefs from 'use-dynamic-refs';

const Example = () =>  {
  const foo = ['random_id_1', 'random_id_2'];
  const [getRef, setRef] =  useDynamicRefs();

  useEffect(() => {
    // Get ref for specific ID 
    const id = getRef('random_id_1');
    console.log(id)
  }, [])

    return ( 
      <>
        {/* Simple set ref. */}
        <span ref={setRef('random_id_3')}></span>

         {/*  Set refs dynamically in Array.map() */}
        { foo.map( eachId => (
          <div key={eachId} ref={setRef(eachId)}>Hello {eachId}</div>))}
      </>
    )
}

export default Example;

Answer 3

You have to use a separate set of hooks for each item, and this means you have to define a component for the items (or else you're using hooks inside a loop, which isn't allowed).

const Item = ({ text }) => {
    const ref = useRef()
    const [ height, setHeight ] = useState()
    useLayoutEffect(() => {
        setHeight( ref.current.getBoundingClientRect().height )
    }, [])
    return <div ref={ref}>{text}</div>
}