React JS: How to animate conditionally rendered components?

问题

Example is a functional component in which I am rendering a div conditionally. I want this div to fade-in when rendered conditionally and fade-out vice versa.

For that, I have maintained two local state variables: render and fadeIn which are computed based on show prop passed down to the Example component.

What I've done is:

• When show prop it true, I set render as true, so the div renders conditionally and after a timeout of 10ms I set fadeIn as true which will set CSS classname for my div as show.
• When show prop it false, I set fadeIn as false, which will set CSS classname for my div as hide and after a timeout of 200ms (transition time in CSS) I set render as false so the div is hidden conditionally.

Code:

interface Props {
  show: boolean;
}

const Example: React.FC<Props> = ({ show, }) => {
  const [render, setRender] = useState(false);
  const [fadeIn, setFadeIn] = useState(false);

  useEffect(() => {
    if (show) {
      // render component conditionally
      setRender(show);

      // change state to for conditional CSS classname which will
      // animate opacity, I had to give a timeout of 10ms else the
      // component shows up abruptly
      setTimeout(() => {
        setFadeIn(show);
      }, 10);
    } else {
      // change state to change component classname for opacity animation
      setFadeIn(false);

      // hide component conditionally after 200 ms
      // because that's the transition time in CSS
      setTimeout(() => {
        setRender(false);
      }, 200);
    }
  }, [
    show,
  ]);

  return (
    <div>
      {render && (
        <div className={`container ${fadeIn ? 'show' : 'hide'}`} />
      )}
    </div>
  );
};

Stylesheet:

.container {
  width: 100px;
  height: 100px;
  background-color: black;
  transition: opacity 0.2s ease;
}

.show {
  opacity: 1;
}

.hide {
  opacity: 0;
}

I believe this is not a good coding practice to achieve the functionality and should maintain only one local state in my component. I need your suggestions on how I can solve this in a better way without using any 3rd Party Library. Thanks :)

回答1:

const [render, setRender] = useState(false);

useEffect(() => {
   if(show) {
     setTimeout(() => {
       setRender(true);
     }, 2000);
   } else {
     setRender(false);
   }
}, [show]);

<div className={cs(s.render, render ? 'show' : undefined)}>
  <p>{content}</p>
</div>

Css:

.render {
  ...,
  visibility: hidden;
  opacity: 0;
  transition: all 0.6s ease;
}

.show {
  visibility: visible;
  opacity: 1;
}

Hope be helpful.

来源：https://stackoverflow.com/questions/61428958/react-js-how-to-animate-conditionally-rendered-components