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?
用React Hooks更新答案
这是两个钩子——一个用于方向(上/下/无)，另一个用于实际位置
像这样使用:
useScrollPosition(position => {
console.log(position)
})
useScrollDirection(direction => {
console.log(direction)
})
下面是钩子:
import { useState, useEffect } from "react"
export const SCROLL_DIRECTION_DOWN = "SCROLL_DIRECTION_DOWN"
export const SCROLL_DIRECTION_UP = "SCROLL_DIRECTION_UP"
export const SCROLL_DIRECTION_NONE = "SCROLL_DIRECTION_NONE"
export const useScrollDirection = callback => {
const [lastYPosition, setLastYPosition] = useState(window.pageYOffset)
const [timer, setTimer] = useState(null)
const handleScroll = () => {
if (timer !== null) {
clearTimeout(timer)
}
setTimer(
setTimeout(function () {
callback(SCROLL_DIRECTION_NONE)
}, 150)
)
if (window.pageYOffset === lastYPosition) return SCROLL_DIRECTION_NONE
const direction = (() => {
return lastYPosition < window.pageYOffset
? SCROLL_DIRECTION_DOWN
: SCROLL_DIRECTION_UP
})()
callback(direction)
setLastYPosition(window.pageYOffset)
}
useEffect(() => {
window.addEventListener("scroll", handleScroll)
return () => window.removeEventListener("scroll", handleScroll)
})
}
export const useScrollPosition = callback => {
const handleScroll = () => {
callback(window.pageYOffset)
}
useEffect(() => {
window.addEventListener("scroll", handleScroll)
return () => window.removeEventListener("scroll", handleScroll)
})
}
用React Hooks更新答案
这是两个钩子——一个用于方向(上/下/无)，另一个用于实际位置
像这样使用:
useScrollPosition(position => {
console.log(position)
})
useScrollDirection(direction => {
console.log(direction)
})
下面是钩子:
import { useState, useEffect } from "react"
export const SCROLL_DIRECTION_DOWN = "SCROLL_DIRECTION_DOWN"
export const SCROLL_DIRECTION_UP = "SCROLL_DIRECTION_UP"
export const SCROLL_DIRECTION_NONE = "SCROLL_DIRECTION_NONE"
export const useScrollDirection = callback => {
const [lastYPosition, setLastYPosition] = useState(window.pageYOffset)
const [timer, setTimer] = useState(null)
const handleScroll = () => {
if (timer !== null) {
clearTimeout(timer)
}
setTimer(
setTimeout(function () {
callback(SCROLL_DIRECTION_NONE)
}, 150)
)
if (window.pageYOffset === lastYPosition) return SCROLL_DIRECTION_NONE
const direction = (() => {
return lastYPosition < window.pageYOffset
? SCROLL_DIRECTION_DOWN
: SCROLL_DIRECTION_UP
})()
callback(direction)
setLastYPosition(window.pageYOffset)
}
useEffect(() => {
window.addEventListener("scroll", handleScroll)
return () => window.removeEventListener("scroll", handleScroll)
})
}
export const useScrollPosition = callback => {
const handleScroll = () => {
callback(window.pageYOffset)
}
useEffect(() => {
window.addEventListener("scroll", handleScroll)
return () => window.removeEventListener("scroll", handleScroll)
})
}
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);
};
我在这里打赌是使用带有新钩子的函数组件来解决它，但不是像以前的答案那样使用useEffect，我认为正确的选择是useLayoutEffect，原因很重要:
签名与useEffect相同，但是它同步触发
在所有DOM突变之后。
这可以在React文档中找到。如果我们使用useEffect代替，并且重新加载已经滚动的页面，则scroll将为false，并且我们的类将不会被应用，从而导致不希望出现的行为。
一个例子:
import React, { useState, useLayoutEffect } from "react"
const Mycomponent = (props) => {
const [scrolled, setScrolled] = useState(false)
useLayoutEffect(() => {
const handleScroll = e => {
setScrolled(window.scrollY > 0)
}
window.addEventListener("scroll", handleScroll)
return () => {
window.removeEventListener("scroll", handleScroll)
}
}, [])
...
return (
<div className={scrolled ? "myComponent--scrolled" : ""}>
...
</div>
)
}
这个问题的一个可能的解决方案是https://codepen.io/dcalderon/pen/mdJzOYq
const Item = (props) => {
const [scrollY, setScrollY] = React.useState(0)
React.useLayoutEffect(() => {
const handleScroll = e => {
setScrollY(window.scrollY)
}
window.addEventListener("scroll", handleScroll)
return () => {
window.removeEventListener("scroll", handleScroll)
}
}, [])
return (
<div class="item" style={{'--scrollY': `${Math.min(0, scrollY/3 - 60)}px`}}>
Item
</div>
)
}
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。
