Animate component with conditional rendering children

Question

I'm a beginner with animations. I have this simple React component that is a panel whose content change based on the state. What I would like to have is an animation when the panel became bigger.

If I use css transitions, it doesn't work. What I have to do to animate the panel (for example its height)?

I look at react-spring but I'm not able to make it works, and I'm asking if it is possible to do what I would using react-spring.

const {useState} = React;

const Example = ({title}) => {
  const [isOpen, setIsOpen] = useState(false);

  return (
    <>
      <div
        className=""
        style={{
          position: "relative",
          width: "100%",
          height: "100%",
          backgroundColor: "tomato"
        }}
      ></div>
      <div
        className="panel"
        style={{
          position: "absolute",
          bottom: 20,
          right: 20,
          backgroundColor: "pink",
          width: 200,
          padding: 15
        }}
      >
        <div>Title</div>

        {!isOpen && (
          <div onClick={() => setIsOpen(true)} style={{ cursor: "pointer" }}>
            Open
          </div>
        )}

        {isOpen && (
          <div style={{ overflowY: "scroll", height: 250 }}>
            Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do
            eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim
            ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut
            aliquip ex ea commodo consequat. Duis aute irure dolor in
            reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla
            pariatur. Excepteur sint occaecat cupidatat non proident, sunt in
            culpa qui officia deserunt mollit anim id est laborum. Sed ut
            perspiciatis unde omnis iste natus error sit voluptatem accusantium
            doloremque laudantium, totam rem aperiam, eaque ipsa quae ab illo
            inventore veritatis et quasi architecto beatae vitae dicta sunt
            explicabo. Nemo enim ipsam voluptatem quia voluptas sit aspernatur
            aut odit aut fugit, sed quia consequuntur magni dolores eos qui
            ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui
            dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed
            quia non numquam eius modi tempora incidunt ut labore et dolore
            magnam aliquam quaerat voluptatem. Ut enim ad minima veniam, quis
            nostrum exercitationem ullam corporis suscipit laboriosam, nisi ut
            aliquid ex ea commodi consequatur? Quis autem vel eum iure
            reprehenderit qui in ea voluptate velit esse quam nihil molestiae
            consequatur, vel illum qui dolorem eum fugiat quo voluptas nulla
            pariatur?
          </div>
        )}

        {isOpen && <div onClick={() => setIsOpen(false)}>Close</div>}
      </div>
    </>
};

// Render it
ReactDOM.render(
  <Example title="Example using Hooks:" />,
  ddocument.getElementById("react"));

html,
body {
  width: 100%;
  height: 100%;
}

#root {
  width: 100%;
  height: 100%;
}

<div id="react"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>

Answer 1

You can use transition and transform to animate height. The one drawback with this approach though is you would have to set a fixed height on the div you wish to animate. I included a little sandbox demo: https://codesandbox.io/s/react-hooks-usestate-forked-l8h91?file=/src/index.js.

const Example = ({title}) => {
  let [isOpen, setIsOpen] = useState(false);

  return (
    <>
      <div
        className=""
        style={{
          position: "relative",
          width: "100%",
          height: "100%",
          backgroundColor: "tomato"
        }}
      ></div>
      
      <div
        className="panel"
        style={{
          position: "absolute",
          bottom: 20,
          right: 20,
          backgroundColor: "pink",
          width: 200,
          padding: 15
        }}
      >

      <div>Title</div>

      {!isOpen && (
        <div onClick={() => setIsOpen(true)} style={{ cursor: "pointer" }}>
          Open
        </div>
      )}

      <div className={`test-box ${!isOpen ? "hideItems" : "showItems"}`}>
        Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
        tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
        veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea
        commodo consequat. Duis aute irure dolor in reprehenderit in voluptate
        velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint
        occaecat cupidatat non proident, sunt in culpa qui officia deserunt
        mollit anim id est laborum. Sed ut perspiciatis unde omnis iste natus
        error sit voluptatem accusantium doloremque laudantium, totam rem
        aperiam, eaque ipsa quae ab illo inventore veritatis et quasi architecto
        beatae vitae dicta sunt explicabo. Nemo enim ipsam voluptatem quia
        voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni
        dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam
        est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit,
        sed quia non numquam eius modi tempora incidunt ut labore et dolore
        magnam aliquam quaerat voluptatem. Ut enim ad minima veniam, quis
        nostrum exercitationem ullam corporis suscipit laboriosam, nisi ut
        aliquid ex ea commodi consequatur? Quis autem vel eum iure reprehenderit
        qui in ea voluptate velit esse quam nihil molestiae consequatur, vel
        illum qui dolorem eum fugiat quo voluptas nulla pariatur?
      </div>

      {isOpen && <div onClick={() => setIsOpen(false)}>Close</div>}
    </div>
    </>
  );
}

Here when you click on open and close, the div will animate in and out. Maybe this can help you get going.