reactjs - useEffect 没有更新依赖值

Question

我有一个组件，我想动态编辑一些样式。当我进入组件时，我希望它顺利增长，当我离开时，我希望它顺利缩短。

这是我的代码：

  const easing = 0.1;
  const outScale = 0.6;
  const inScale = 1;
  let targetScale = outScale;
  let elementScale = targetScale;
  let innerScale = 1 / elementScale;

  const [parentTransformStyle, setParentTransformStyle] = useState(
    `scale(${elementScale})`
  );
  const [innerTransformStyle, setInnerTransformStyle] = useState(
    `scale(${innerScale})`
  );
  const requestRef = useRef();

  const onPointOverEvent = () => {
    targetScale = inScale;
    console.log("over", inScale, targetScale);
  };

  const onPointerOutEvent = () => {
    targetScale = outScale;
    console.log("out", outScale, targetScale);
  };

  const animate = () => {
    console.log("animate", targetScale);

    elementScale += (targetScale - elementScale) * easing;
    innerScale = 1 / elementScale;

    setParentTransformStyle(`scale(${elementScale})`);
    setInnerTransformStyle(`scale(${innerScale})`);

    requestAnimationFrame(animate);
  };

  useEffect(() => {
    requestRef.current = requestAnimationFrame(animate);
    return () => cancelAnimationFrame(requestRef.current);
  }, []);

targetScale当鼠标悬停在元素中以及鼠标离开元素时，应该更新该变量。

如果我在事件侦听器中打印该值，则该值是正确的。但是在animate函数内部，它具有初始值。有人可以指出我所缺少的吗？

标签： reactjsreact-hooks

Answer 1

有什么理由你不能使用 CSS 转换而不是自己做动画吗？

例子：

function MyComponent() {
  const [innerTransformStyle, setInnerTransformStyle] = React.useState(
    `scale(${0.6})`
  );

  const onPointOverEvent = () => {
    setInnerTransformStyle(`scale(${1})`);
  };

  const onPointerOutEvent = () => {
    setInnerTransformStyle(`scale(${0.6})`);
  };
  
  return (
    <div className="parent">
      <div className="element" style={{transform: innerTransformStyle}} onPointerOut={onPointerOutEvent} onPointerOver={onPointOverEvent}></div>
    </div>
  );
}

ReactDOM.render(<MyComponent/>, document.getElementById("app"));

.parent {
  width: 100px;
  height: 100px;
  background-color: #f00;
}

.element {
  width: 100px;
  height: 100px;
  background-color: #0f0;
  transition: transform 1s;
}

<script src="https://unpkg.com/react@16/umd/react.development.js" crossorigin></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js" crossorigin></script>

<div id="app"></div>