我正在使用LitElement创建自定义Web组件。我对此很陌生,因此决定尝试制作图像幻灯片。我使用了W3Schools slideshow as reference 同时对其进行修改以用作LitElement。 问题是,当我尝试使用document.getElementByClassName时,我什么也没得到。因为我正在使用Shadow DOM,所以我对这个问题很熟悉,因此我将其更改为this.shadowRoot.getElementsByClassName。不幸的是,我被告知我要使用的不是函数。使用LitElement和shadow dom时如何按类名获取元素?如果您想查看我的组件的外观,请使用以下代码:
import { LitElement, html} from '@polymer/lit-element';
class ImageGalleryElement extends LitElement {
static get properties() { return {
slideIndex: { type: Number },
}};
constructor(){
super();
this.slideIndex=1;
this.showSlides(this.slideIndex);
}
// Next/previous controls
plusSlides(n) {
this.showSlides(this.slideIndex += n);
}
// Thumbnail image controls
currentSlide(n) {
this.showSlides(this.slideIndex = n);
}
showSlides(n) {
var i;
console.dir(this.shadowRoot);
var slides = this.shadowRoot.getElementsByClassName("mySlides");
console.dir(slides);
var dots = this.shadowRoot.getElementsByClassName("dot");
if (n > slides.length) {this.slideIndex = 1}
if (n < 1) {this.slideIndex = slides.length}
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
for (i = 0; i < dots.length; i++) {
dots[i].className = dots[i].className.replace(" active", "");
}
slides[this.slideIndex-1].style.display = "block";
dots[this.slideIndex-1].className += " active";
}
render(){
return html`
<style>
* {box-sizing:border-box}
/* Slideshow container */
.slideshow-container {
max-width: 1000px;
position: relative;
margin: auto;
}
/* Hide the images by default */
.mySlides {
display: none;
}
/* Next & previous buttons */
.prev, .next {
cursor: pointer;
position: absolute;
top: 50%;
width: auto;
margin-top: -22px;
padding: 16px;
color: white;
font-weight: bold;
font-size: 18px;
transition: 0.6s ease;
border-radius: 0 3px 3px 0;
user-select: none;
}
/* Position the "next button" to the right */
.next {
right: 0;
border-radius: 3px 0 0 3px;
}
/* On hover, add a black background color with a little bit see-through */
.prev:hover, .next:hover {
background-color: rgba(0,0,0,0.8);
}
/* Caption text */
.text {
color: #f2f2f2;
font-size: 15px;
padding: 8px 12px;
position: absolute;
bottom: 8px;
width: 100%;
text-align: center;
}
/* Number text (1/3 etc) */
.numbertext {
color: #f2f2f2;
font-size: 12px;
padding: 8px 12px;
position: absolute;
top: 0;
}
/* The dots/bullets/indicators */
.dot {
cursor: pointer;
height: 15px;
width: 15px;
margin: 0 2px;
background-color: #bbb;
border-radius: 50%;
display: inline-block;
transition: background-color 0.6s ease;
}
.active, .dot:hover {
background-color: #717171;
}
/* Fading animation */
.fade {
-webkit-animation-name: fade;
-webkit-animation-duration: 1.5s;
animation-name: fade;
animation-duration: 1.5s;
}
@-webkit-keyframes fade {
from {opacity: .4}
to {opacity: 1}
}
@keyframes fade {
from {opacity: .4}
to {opacity: 1}
}
</style>
<!-- Slideshow container -->
<div class="slideshow-container">
<!-- Full-width images with number and caption text -->
<div class="mySlides fade">
<div class="numbertext">1 / 3</div>
<img src="../../img/img-snow-wide" style="width:100%">
<div class="text">Caption Text</div>
</div>
<div class="mySlides fade">
<div class="numbertext">2 / 3</div>
<img src="../../img/img-nature-wide" style="width:100%">
<div class="text">Caption Two</div>
</div>
<div class="mySlides fade">
<div class="numbertext">3 / 3</div>
<img src="../../img/img-mountains-wide" style="width:100%">
<div class="text">Caption Three</div>
</div>
<!-- Next and previous buttons -->
<a class="prev" @click="${this.plusSlides(-1)}" >❮</a>
<a class="next" @click="${this.plusSlides(1)}">❯</a>
</div>
<br>
<!-- The dots/circles -->
<div style="text-align:center">
<span class="dot" @click="${this.currentSlide(1)}"></span>
<span class="dot" @click="${this.currentSlide(2)}"></span>
<span class="dot" @click="${this.currentSlide(3)}"></span>
</div>
`;
}
}
// Register the element with the browser
customElements.define('image-gallery-element', ImageGalleryElement);
答案 0 :(得分:8)
getElementsByClassName()
方法仅适用于HTML文档或元素。
shadowRoot
是文档片段,不是文档也不是HTML元素。
您应该使用querySelectorAll()
。
答案 1 :(得分:0)
LitElement 还提供了自己方便的装饰器来访问节点:@query
, @queryAll
, and @queryAsync
decorators
但我当然理解你是否想保持原味:)