What is the usage of material-ui useScrollTrigger with child target ref?

Question

I am trying to use material-ui's useScrollTrigger with a target other than window like so:

export default props => {
    let contentRef = React.createRef();

    const scrollTrigger = useScrollTrigger({ target: contentRef.current });

    return (
        <React.Fragment>
            <CustomHeader shrink={scrollTrigger} />

            <div ref={contentRef}>
                {props.children}
            </div>
        </React.Fragment>
    );
};

This causes an error to be thrown because contentRef.current is null when useScrollTrigger is called. What is the proper usage of this utility with child elements as a target?

Answer 1

你是对的，因为组件第一次呈现 contentRef.current 是空的，所以会抛出一个错误。

我们需要两件事，一个是对目标 Element 的引用，另一个是重新渲染以便再次计算 scrollTrigger。换句话说，我们需要一个状态。

以下代码将起作用

export default props => {

    // please keep it undefined here to not make useScrollTrigger throw an error on first render 
    const [scrollTarget, setScrollTarget] = useState(undefined) 
    const scrollTrigger = useScrollTrigger({ target: scrollTarget });

    return (
        <React.Fragment>
            <CustomHeader shrink={scrollTrigger} />

            <div ref={node => {
                if (node) {
                    setScrollTarget(node);
                }
            }}>
                {props.children}
            </div>
        </React.Fragment>
    );
};