我在React中构建了一个组件，它应该在窗口滚动上更新自己的风格，以创建视差效果。
组件渲染方法是这样的:
function() {
let style = { transform: 'translateY(0px)' };
window.addEventListener('scroll', (event) => {
let scrollTop = event.srcElement.body.scrollTop,
itemTranslate = Math.min(0, scrollTop/3 - 60);
style.transform = 'translateY(' + itemTranslate + 'px)');
});
return (
<div style={style}></div>
);
}
这是行不通的，因为React不知道组件已经更改，因此组件不会重新呈现。
我已经尝试在组件的状态中存储itemTranslate的值，并在滚动回调中调用setState。然而，这使得滚动无法使用，因为它非常慢。
有什么建议吗?
您应该在componentDidMount中绑定侦听器，这样它只创建一次。您应该能够在状态中存储样式，侦听器可能是性能问题的原因。
就像这样:
componentDidMount: function() {
window.addEventListener('scroll', this.handleScroll);
},
componentWillUnmount: function() {
window.removeEventListener('scroll', this.handleScroll);
},
handleScroll: function(event) {
let scrollTop = event.srcElement.body.scrollTop,
itemTranslate = Math.min(0, scrollTop/3 - 60);
this.setState({
transform: itemTranslate
});
},
用钩子:
import React, { useEffect, useState } from 'react';
function MyApp () {
const [offset, setOffset] = useState(0);
useEffect(() => {
const onScroll = () => setOffset(window.pageYOffset);
// clean up code
window.removeEventListener('scroll', onScroll);
window.addEventListener('scroll', onScroll, { passive: true });
return () => window.removeEventListener('scroll', onScroll);
}, []);
console.log(offset);
};
constructor() {
super()
this.state = {
change: false
}
}
componentDidMount() {
window.addEventListener('scroll', this.handleScroll);
console.log('add event');
}
componentWillUnmount() {
window.removeEventListener('scroll', this.handleScroll);
console.log('remove event');
}
handleScroll = e => {
if (window.scrollY === 0) {
this.setState({ change: false });
} else if (window.scrollY > 0 ) {
this.setState({ change: true });
}
}
render() {return (<div className="main" style={{boxShadow: this.state.change ?0px 6px 12px rgba(3,109,136,0.14):none}} ></div> .
我就是这么做的，而且效果很好。
一个使用classNames, React挂钩useEffect, useState和styles -jsx的例子:
import classNames from 'classnames'
import { useEffect, useState } from 'react'
const Header = _ => {
const [ scrolled, setScrolled ] = useState()
const classes = classNames('header', {
scrolled: scrolled,
})
useEffect(_ => {
const handleScroll = _ => {
if (window.pageYOffset > 1) {
setScrolled(true)
} else {
setScrolled(false)
}
}
window.addEventListener('scroll', handleScroll)
return _ => {
window.removeEventListener('scroll', handleScroll)
}
}, [])
return (
<header className={classes}>
<h1>Your website</h1>
<style jsx>{`
.header {
transition: background-color .2s;
}
.header.scrolled {
background-color: rgba(0, 0, 0, .1);
}
`}</style>
</header>
)
}
export default Header
下面是另一个使用HOOKS fontAwesomeIcon和Kendo UI React的例子
[![这里截图][1]][1]
import { FontAwesomeIcon } from '@fortawesome/react-fontawesome';
const ScrollBackToTop = () => {
const [show, handleShow] = useState(false);
useEffect(() => {
window.addEventListener('scroll', () => {
if (window.scrollY > 1200) {
handleShow(true);
} else handleShow(false);
});
return () => {
window.removeEventListener('scroll');
};
}, []);
const backToTop = () => {
window.scroll({ top: 0, behavior: 'smooth' });
};
return (
<div>
{show && (
<div className="backToTop text-center">
<button className="backToTop-btn k-button " onClick={() => backToTop()} >
<div className="d-none d-xl-block mr-1">Top</div>
<FontAwesomeIcon icon="chevron-up"/>
</button>
</div>
)}
</div>
);
};
export default ScrollBackToTop;```
[1]: https://i.stack.imgur.com/ZquHI.png
