javascript - 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"/>