Javascript 如何在滚动到页面中的某个位置后动态呈现元素？

我想我的“emailForm”组件呈现在我的导航栏后，用户滚动到“洗衣区”的开始，有人知道怎么做吗

我尝试了

{window.scrollY>500px？电子邮件表单：'}

但是它不起作用，我对react还不是很熟悉，所以也许你可以帮我找到实现它的正确方法

容器：

从“React”导入React，{Component}；
//组成部分
从“../components/styledComponents/Section”导入节；
从“./组件/EmailForm”导入EmailForm
从“./containers/Navbar”导入导航栏；
导出默认类扩展组件{
render（）{
const{iconStyle}=这个；
返回(
{/*头段*/}
标题
佩雷斯·莫伊：
{/*洗衣房组*/}
这是一场暴风雨，利用了秋天。
完成无休止的拉维里之旅……为临时雇员提供免费服务

{/* 	 */}
);
}
}

您好，请检查此ScrollExample和ScrollChild组件。我在ScrollExample组件中使用了ScrollChild。当您向下滚动到200时，屏幕上将显示ScrollChild组件

滚动示例组件

import * as React from "react";
import ScrollChild from "./ScrollChild";

export default class ScrollExample extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
            isChildActive: false
        }
    }

    componentDidMount() {
        window.addEventListener('scroll', this.handleScroll);
    }

    componentWillUnmount() {
        window.removeEventListener('scroll', this.handleScroll);
    }

    handleScroll = (event) => {
        let scrollTop = window.scrollY;

        if (scrollTop > 200)
            this.setState({isChildActive: true});
        else
            this.setState({isChildActive: false});
    };

    render() {
        return (
            <div style={{height: 2000}}>
                Scroll down to show the EmailForm
                {
                    this.state.isChildActive ? <ScrollChild/> : null
                }
            </div>
        );
    }
}

import React, {useEffect, useState} from 'react';

function ScrollChild(props) {
    return (
        <div style={{backgroundColor: '#1569C7', color: '#ffffff', width: 500, marginTop: 300, padding: 20}}>
            THIS IS A DUMMY TEXT
            <h1>How to dynamically render an element after scrolling to a certain position in a page?</h1>

            I would like my "emailForm" component to render on my Navbar after user scrolled to beginning of
            "laundry section", does someone know how to do that?

            I tried window.scrollY > 500px ? EmailForm : "" But it doesn't work, I am not very familiar yet with
            react so maybe you could help me figure out the right method to achieve it?

            I would like my "emailForm" component to render on my Navbar after user scrolled to beginning of
            "laundry section", does someone know how to do that?

            I tried window.scrollY > 500px ? EmailForm : "" But it doesn't work, I am not very familiar yet with
            react so maybe you could help me figure out the right method to achieve it?

            I would like my "emailForm" component to render on my Navbar after user scrolled to beginning of
            "laundry section", does someone know how to do that?

            I tried window.scrollY > 500px ? EmailForm : "" But it doesn't work, I am not very familiar yet with
            react so maybe you could help me figure out the right method to achieve it?

            I would like my "emailForm" component to render on my Navbar after user scrolled to beginning of
            "laundry section", does someone know how to do that?

            I tried window.scrollY > 500px ? EmailForm : "" But it doesn't work, I am not very familiar yet with
            react so maybe you could help me figure out the right method to achieve it?
        </div>
    );
}

export default ScrollChild;

import*as React from“React”；
从“/ScrollChild”导入ScrollChild；
导出默认类ScrollExample扩展了React.Component{
建造师（道具）{
超级（道具）；
此.state={
Ischildative:错误
}
}
componentDidMount（）{
window.addEventListener（'scroll'，this.handleScroll）；
}
组件将卸载（）{
window.removeEventListener（'scroll'，this.handleScroll）；
}
handleScroll=（事件）=>{
让scrollTop=window.scrollY；
如果（滚动顶部>200）
this.setState（{ischildative:true}）；
其他的
this.setState（{ischildative:false}）；
};
render（）{
返回(
向下滚动以显示电子邮件表单
{
this.state.ischildative？：null
}
);
}
}

滚动子组件

import * as React from "react";
import ScrollChild from "./ScrollChild";

export default class ScrollExample extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
            isChildActive: false
        }
    }

    componentDidMount() {
        window.addEventListener('scroll', this.handleScroll);
    }

    componentWillUnmount() {
        window.removeEventListener('scroll', this.handleScroll);
    }

    handleScroll = (event) => {
        let scrollTop = window.scrollY;

        if (scrollTop > 200)
            this.setState({isChildActive: true});
        else
            this.setState({isChildActive: false});
    };

    render() {
        return (
            <div style={{height: 2000}}>
                Scroll down to show the EmailForm
                {
                    this.state.isChildActive ? <ScrollChild/> : null
                }
            </div>
        );
    }
}

import React, {useEffect, useState} from 'react';

function ScrollChild(props) {
    return (
        <div style={{backgroundColor: '#1569C7', color: '#ffffff', width: 500, marginTop: 300, padding: 20}}>
            THIS IS A DUMMY TEXT
            <h1>How to dynamically render an element after scrolling to a certain position in a page?</h1>

            I would like my "emailForm" component to render on my Navbar after user scrolled to beginning of
            "laundry section", does someone know how to do that?

            I tried window.scrollY > 500px ? EmailForm : "" But it doesn't work, I am not very familiar yet with
            react so maybe you could help me figure out the right method to achieve it?

            I would like my "emailForm" component to render on my Navbar after user scrolled to beginning of
            "laundry section", does someone know how to do that?

            I tried window.scrollY > 500px ? EmailForm : "" But it doesn't work, I am not very familiar yet with
            react so maybe you could help me figure out the right method to achieve it?

            I would like my "emailForm" component to render on my Navbar after user scrolled to beginning of
            "laundry section", does someone know how to do that?

            I tried window.scrollY > 500px ? EmailForm : "" But it doesn't work, I am not very familiar yet with
            react so maybe you could help me figure out the right method to achieve it?

            I would like my "emailForm" component to render on my Navbar after user scrolled to beginning of
            "laundry section", does someone know how to do that?

            I tried window.scrollY > 500px ? EmailForm : "" But it doesn't work, I am not very familiar yet with
            react so maybe you could help me figure out the right method to achieve it?
        </div>
    );
}

export default ScrollChild;

import React，{useffect，useState}来自“React”；
函数滚动子（道具）{
返回(
这是一个虚拟文本
如何在滚动到页面中的某个位置后动态呈现元素？
我想我的“emailForm”组件呈现在我的导航栏后，用户滚动到的开始
“洗衣房”，有人知道怎么做吗？
我试过window.scrollY>500px？EmailForm:“”但不起作用，我还不太熟悉它
那么你能帮我找出正确的方法来实现它吗？
我想我的“emailForm”组件呈现在我的导航栏后，用户滚动到的开始
“洗衣房”，有人知道怎么做吗？
我试过window.scrollY>500px？EmailForm:“”但不起作用，我还不太熟悉它
那么你能帮我找出正确的方法来实现它吗？
我想我的“emailForm”组件呈现在我的导航栏后，用户滚动到的开始
“洗衣房”，有人知道怎么做吗？
我试过window.scrollY>500px？EmailForm:“”但不起作用，我还不太熟悉它
那么你能帮我找出正确的方法来实现它吗？
我想我的“emailForm”组件呈现在我的导航栏后，用户滚动到的开始
“洗衣房”，有人知道怎么做吗？
我试过window.scrollY>500px？EmailForm:“”但不起作用，我还不太熟悉它
那么你能帮我找出正确的方法来实现它吗？
);
}
导出默认滚动子对象；

我现在没有示例代码，但您可以这样做：

---

滚动时，您可以检查元素是否可见（带有位置和滚动位置）。如果是，您可以在每次状态更改时执行jQuery动画，它将调用组件的渲染。但是在渲染中，不会有任何更改，因为渲染不依赖于此.state.scrollTop

要解决此问题，您需要做两件事： 1.当用户滚动超过阈值（500px）时更新状态 2.在

render（）

方法中使用此新状态值重新渲染组件

我创建了一个示例，当

this.state.showEmailForm

更改时，我会更改表单的不透明度。您可以在下面的示例中看到和看到：

类应用程序扩展了React.Component{
建造师（道具）{
超级（道具）；
此.state={
showmailform:false，
};
}
componentDidMount=（）=>{
window.addEventListener（“滚动”，this.onScroll）；
};
组件将卸载=（）=>{
removeEventListener（“滚动”，this.onScroll）；
};
onScroll=（）=>{
这是我的国家({
showEmailForm:window.scrollY>500，
});
};
render（）{
返回(

{" "}
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