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javascript - 触发滚动事件时无法平滑过渡背景颜色

问题描述

我正在尝试使用 react 为我的一个项目创建一个固定的标题。打开网页时，标题的背景颜色应该是透明的，但向下滚动时，它应该将其颜色更改为黑色。我设法使过渡平滑，同时将背景颜色从透明更改为黑色（当我向下滚动时），但是，当背景颜色从黑色变为透明时（当我向上滚动时），我无法使过渡平滑。

这是我的代码：

import React from 'react';
import Navbar from '../Navbar/Navbar.js';
import logo from '../images/nsut_logo.png';

class Header extends React.Component {
    constructor() {
        super();
        this.state = {
            header: false
        };
        this.handleScroll = this.handleScroll.bind(this);
    }

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

    handleScroll(event) {
        if (window.pageYOffset > 0) {
              this.setState({ header: true });   
        }
        else{
              this.setState({ header: false });
        }
    }

    
    
    render() {
        return (
            <header onScroll={this.handleScroll}>
                <div className={this.state.header ? "Header-Site-Title-Active" : "Header-Site-Title"}>
                    <img className = "Header-logo" src={logo} />
                    
                    <div className="Department-Name">
                        <h1 >
                            <b>Department Of Computer Science And Engineering</b>
                            <br/>
                        </h1>
                        <h3>
                            Netaji Subhas University of Technology
                        </h3>
                        
                    </div>          
                    <Navbar />
                </div>
            </header>
        );
    }
}

export default Header;

这是我的 CSS 文件：

header{
  top: 0;
  padding-bottom: 1%;
  position: fixed;
  z-index: 5;
  height: 17vh;
}


@keyframes bgChangeDown {
  0% {background-color: none;}
  100% {background-color: black;}
}

@keyframes bgChangeUp {
  0% {background-color: inherit;}
  100% {background-color: none;}
}



.Handle-Site-Title {
  height: 100px;
    width: 100vw;
  top: 0;
  animation-name: bgChangeUp;
  animation-duration: 2s;
  animation-iteration-count: 1;
  transition: ease-in 1.5s;
  animation-fill-mode: forwards;
}


.Header-Site-Title-Active {
    height: 100px;
    width: 100vw;
  top: 0;
  animation-name: bgChangeDown;
  animation-duration: 2s;
  animation-iteration-count: 1;
  animation-fill-mode: forwards;
  transition: ease-in 1.5s;
}

.Header-logo{
    height:100px;
    padding: 5px 10px 0 5px;
    margin: 0;
    display: inline;
    float: left;
}


.Department-Name{
    margin: 0;
    margin-bottom: 5px;
    height: 100px;
    float: left;
    display: inline;
    color: white;
}

.Department-Name h3{
    margin-bottom: 15px;
    margin-top: -17px
}


.hamburger{
    position: fixed;
    cursor: pointer;
    margin: 5px;
    right: 5%;
    top: 5%;
}



.line{
    width: 30px;
    height: 3px;
    background: white;
    margin: 5px;
}


.sidenav {
  height: 100%; /* 100% Full-height */
  width: 0; /* 0 width - change this with JavaScript */
  position: fixed; /* Stay in place */
  z-index: 1; /* Stay on top */
  top: 0; /* Stay at the top */
  right: 0;
  background-color: black; /* Black*/
  overflow-x: hidden; /* Disable horizontal scroll */
  padding-top: 60px; /* Place content 60px from the top */
  transition: 0.5s; /* 0.5 second transition effect to slide in the sidenav */
}


.sidenav-active {
  height: 100%; /* 100% Full-height */
  width: 250px; /* 0 width - change this with JavaScript */
  position: fixed; /* Stay in place */
  z-index: 1; /* Stay on top */
  top: 0; /* Stay at the top */
  right: 0;
  background-color: black; /* Black*/
  overflow-x: hidden; /* Disable horizontal scroll */
  padding-top: 60px; /* Place content 60px from the top */
  transition: 0.5s; /* 0.5 second transition effect to slide in the sidenav */

}


/* The navigation menu links */
.sidenav a, .sidenav-active a {
  padding: 8px 8px 8px 32px;
  text-decoration: none;
  font-size: 25px;
  color: white;
  display: block;
  transition: 0.3s;
}

/* When you mouse over the navigation links, change their color */
.sidenav a:hover, .sidenav-active a:hover {
  color: #f1f1f1;
}

/* Position and style the close button (top right corner) */
.sidenav .closebtn, .sidenav-active .closebtn {
  position: absolute;
  top: 0;
  right: 25px;
  font-size: 36px;
  margin-left: 50px;
}




@media screen and (max-height: 450px) {
  .sidenav {padding-top: 15px;}
  .sidenav a {font-size: 18px;}
}

我还在学习 React，所以也可以随意提出一种新方法。

标签： javascripthtmlcssreactjsreact-native

解决方案

您在 React 组件中应用的类是Header-Site-Title-Active，Header-Site-Title但在您的 CSS 中，您的bgChangeUp动画被分配给Handle-Site-Title该类，而不是Header-Site-Title：

.Handle-Site-Title {
  height: 100px;
    width: 100vw;
  top: 0;
  animation-name: bgChangeUp;
  animation-duration: 2s;
  animation-iteration-count: 1;
  transition: ease-in 1.5s;
  animation-fill-mode: forwards;
}

.Header-Site-Title-Active {
    height: 100px;
    width: 100vw;
  top: 0;
  animation-name: bgChangeDown;
  animation-duration: 2s;
  animation-iteration-count: 1;
  animation-fill-mode: forwards;
  transition: ease-in 1.5s;
}

此外，使用 CSS 过渡可以更轻松地实现此效果：

.Header-Site-Title {
  ...
  background-color: transparent;
  transition: background-color ease-in 1.5s;
  ...
}

.Header-Site-Title-Active {
  ...
  background-color: rgba(0,0,0,black);
  ...
}

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