上一个按钮导致幻灯片消失

Question

我制作了一个简单的 w3 Schools 幻灯片，编辑了 by user Sinisake 并编辑了样式以删除幻灯片计数器和标题，并编辑了上一个和下一个按钮以占据幻灯片每一侧的一半滑动，光标更改为表示单击。

唯一的问题是，当您在第一张幻灯片上单击 'previous' 时，previousElementSibling 调用了一个不存在的元素，整个幻灯片就消失了。我知道这是因为我改变了上一个和下一个位置，但我不知道为什么。

另外，我用 display: none 隐藏了点，但是如果我从 html 和 javascript 中删除它们，幻灯片就会中断。

我对CSS和html略知一二，但对Javascript还是个新手，感谢大家的耐心和帮助。

我的代码在下面，页面也托管在这里：http://dominicfortunato.com/Template%20Studio%20Site/index-updated-slideshow-2.html

(function() {

  init(); //on page load - show first slide, hidethe rest

  function init() {

    parents = document.getElementsByClassName('slideshow-container');

    for (j = 0; j < parents.length; j++) {
      var slides = parents[j].getElementsByClassName("mySlides");
      var dots = parents[j].getElementsByClassName("dot");
      slides[0].classList.add('active-slide');
      dots[0].classList.add('active');
    }
  }

  dots = document.getElementsByClassName('dot'); //dots functionality

  for (i = 0; i < dots.length; i++) {

    dots[i].onclick = function() {

      slides = this.parentNode.parentNode.getElementsByClassName("mySlides");

      for (j = 0; j < this.parentNode.children.length; j++) {
        this.parentNode.children[j].classList.remove('active');
        slides[j].classList.remove('active-slide');
        if (this.parentNode.children[j] == this) {
          index = j;
        }
      }
      this.classList.add('active');
      slides[index].classList.add('active-slide');

    }
  }
//prev/next functionality
  links = document.querySelectorAll('.slideshow-container a');

  for (i = 0; i < links.length; i++) {
    links[i].onclick = function() {
      current = this.parentNode;

      var slides = current.getElementsByClassName("mySlides");
      var dots = current.getElementsByClassName("dot");
      curr_slide = current.getElementsByClassName('active-slide')[0];
      curr_dot = current.getElementsByClassName('active')[0];
      curr_slide.classList.remove('active-slide');
      curr_dot.classList.remove('active');
      if (this.className == 'next') {

        if (curr_slide.nextElementSibling.classList.contains('mySlides')) {
          curr_slide.nextElementSibling.classList.add('active-slide');
          curr_dot.nextElementSibling.classList.add('active');
        } else {
          slides[0].classList.add('active-slide');
          dots[0].classList.add('active');
        }

      }

      if (this.className == 'prev') {

    if (curr_slide.previousElementSibling.classList.contains('mySli‌des')) {
          curr_slide.previousElementSibling.classList.add('active-slide');
          curr_dot.previousElementSibling.classList.add('active');
        } else {
          slides[slides.length - 1].classList.add('active-slide');
          dots[slides.length - 1].classList.add('active');
        }

      }

    }

  }
})();

 /* Slideshow container */
 
 
.slideshow-container {
  max-width: 80%;
  position: relative;
  padding-top: 3%;
  padding-bottom: 2%;
  margin: auto;
}

/* Next & previous buttons */
.prev, .next {
  cursor: url('Images/arrow.png'), w-resize;
  float: left;
  position: absolute;
  width: 50%;
  height: 90%;
  margin-right: auto;
  margin-left: auto;
  transition: 0.3s ease;
  border-radius: 0 0px 0px 0;
}

/* Position the "next button" to the right */
.next {
  cursor: url('Images/arrow.png'), e-resize;
  right: 0;
  border-radius: 0px 0 0 0px;

}

/* On hover, add a black background color with a little bit see-through */
.prev:hover, .next:hover {
  background-color: rgba(0,0,0,0);
}

.mySlides {
  display:none;
}
.active-slide {
  display:block;
}

.active-slide-1 {
  display:block;
}

.dot {
  cursor:pointer;
  height: 13px;
  width: 13px;
  margin: 0 2px;
  background-color: #bbb;
  border-radius: 50%;
  display: none;
  transition: background-color 0.6s ease;
}

.active, .dot:hover {
  background-color: #717171;
}


/* Fading animation */
.fade {
  -webkit-animation-name: fade;
  -webkit-animation-duration: 0.2s;
  animation-name: fade;
  animation-duration: 0.2s;
}

@-webkit-keyframes fade {
  from {opacity: .1}
  to {opacity: 1}
}

@keyframes fade {
  from {opacity: .4}
  to {opacity: 1}
}

.text-container {
 z-index: 300;
 max-width: 80%;
 float: center;
 text-align: left;
 position: relative;
 margin-right: auto;
 margin-left: auto;
 padding-bottom: 2%;
 font-family:"GT Walsheim", Calibri, sans-serif;
}

.project-description {
 width: 100%;
 font-size: 36px;
 margin-left: 20px;
 font-family:"GT Walsheim", Calibri, sans-serif;
 display: inline;
}

.project-title {
 width: 100%;
 display: inline;
 margin-left: 150px;
 text-decoration: underline;
 font-size: 36px; 
}

<div class="slideshow-container">
  <a class="prev" ></a>
  <a class="next"></a>

  <div class="mySlides fade">
    <img src="http://www.w3schools.com/howto/img_mountains_wide.jpg" style="width:100%">
  </div>

  <div class="mySlides fade">
    <img src="http://www.w3schools.com/howto/img_fjords_wide.jpg" style="width:100%">
  </div>

  <div class="mySlides fade">
    <img src="http://www.w3schools.com/howto/img_nature_wide.jpg" style="width:100%">
  </div>

  <div class="mySlides fade">
    <img src="http://placehold.it/1000x350" style="width:100%">
  </div>

<div style="text-align:center">
  <span class="dot"></span>
  <span class="dot"></span>
  <span class="dot"></span>
  <span class="dot"></span>
</div>  
</div>
<div class="text-container">
 <div class="project-title">Rust Belt Riders</div>
 <div class="project-description">Identity for Rust Belt Riders, a waste management and composting company from Cleveland. </div>
  </div>

<br>

<div class="slideshow-container">
  <a class="prev" ></a>
  <a class="next"></a>

  <div class="mySlides fade">
    <img src="http://www.w3schools.com/howto/img_mountains_wide.jpg" style="width:100%">
  </div>

  <div class="mySlides fade">
    <img src="http://www.w3schools.com/howto/img_fjords_wide.jpg" style="width:100%">
  </div>

  <div class="mySlides fade">
    <img src="http://www.w3schools.com/howto/img_nature_wide.jpg" style="width:100%">
  </div>

  <div class="mySlides fade">
    <img src="http://placehold.it/1000x350" style="width:100%">
  </div>

<div style="text-align:center">
  <span class="dot"></span>
  <span class="dot"></span>
  <span class="dot"></span>
</div>  
</div>
<div class="text-container">
 <div class="project-title">Rust Belt Riders</div>
 <div class="project-description">Identity for Rust Belt Riders, a waste management and composting company from Cleveland. </div>
  </div>

<br>

Answer 1

这对我有用：（您可能忘记了第二个滑块中的一个点）。看看这个 Fiddle：https://jsfiddle.net/prtuxoxx/

<div class="slideshow-container">
        <a class="prev" ></a>
        <a class="next"></a>

        <div class="mySlides fade">
          <img src="http://www.w3schools.com/howto/img_mountains_wide.jpg" style="width:100%">
        </div>

        <div class="mySlides fade">
          <img src="http://www.w3schools.com/howto/img_fjords_wide.jpg" style="width:100%">
        </div>

        <div class="mySlides fade">
          <img src="http://www.w3schools.com/howto/img_nature_wide.jpg" style="width:100%">
        </div>

        <div class="mySlides fade">
          <img src="http://placehold.it/1000x350" style="width:100%">
        </div>

      <div style="text-align:center">
        <span class="dot"></span>
        <span class="dot"></span>
        <span class="dot"></span>
        <span class="dot"></span>
      </div>  
    </div>
    <div class="text-container">
        <div class="project-title">Rust Belt Riders</div>
        <div class="project-description">Identity for Rust Belt Riders, a waste management and composting company from Cleveland. </div>
    </div>

      <br>

    <div class="slideshow-container">
        <a class="prev" ></a>
        <a class="next"></a>

        <div class="mySlides fade">
          <img src="http://www.w3schools.com/howto/img_mountains_wide.jpg" style="width:100%">
        </div>

        <div class="mySlides fade">
          <img src="http://www.w3schools.com/howto/img_fjords_wide.jpg" style="width:100%">
        </div>

        <div class="mySlides fade">
          <img src="http://www.w3schools.com/howto/img_nature_wide.jpg" style="width:100%">
        </div>

        <div class="mySlides fade">
          <img src="http://placehold.it/1000x350" style="width:100%">
        </div>

      <div style="text-align:center">
        <span class="dot"></span>
        <span class="dot"></span>
        <span class="dot"></span>
        <span class="dot"></span>
      </div>  
    </div>
    <div class="text-container">
        <div class="project-title">Rust Belt Riders</div>
        <div class="project-description">Identity for Rust Belt Riders, a waste management and composting company from Cleveland. </div>
    </div>

和 JS:

(function() {

      init(); //on page load - show first slide, hidethe rest

      function init() {

        parents = document.getElementsByClassName('slideshow-container');

        for (j = 0; j < parents.length; j++) {
          var slides = parents[j].getElementsByClassName("mySlides");
          var dots = parents[j].getElementsByClassName("dot");
          slides[0].classList.add('active-slide');
          dots[0].classList.add('active');
        }
      }

      dots = document.getElementsByClassName('dot'); //dots functionality

      for (i = 0; i < dots.length; i++) {

        dots[i].onclick = function() {

          slides = this.parentNode.parentNode.getElementsByClassName("mySlides");

          for (j = 0; j < this.parentNode.children.length; j++) {
            this.parentNode.children[j].classList.remove('active');
            slides[j].classList.remove('active-slide');
            if (this.parentNode.children[j] == this) {
              index = j;
            }
          }
          this.classList.add('active');
          slides[index].classList.add('active-slide');

        }
      }
    //prev/next functionality
      links = document.querySelectorAll('.slideshow-container a');

      for (i = 0; i < links.length; i++) {
        links[i].onclick = function() {
          current = this.parentNode;

          var slides = current.getElementsByClassName("mySlides");
          var dots = current.getElementsByClassName("dot");
          curr_slide = current.getElementsByClassName('active-slide')[0];
          curr_dot = current.getElementsByClassName('active')[0];
          curr_slide.classList.remove('active-slide');
          curr_dot.classList.remove('active');
          if (this.className == 'next') {
            console.log('next ', curr_slide);
            if (curr_slide.nextElementSibling.classList.contains('mySlides')) {
              curr_slide.nextElementSibling.classList.add('active-slide');
              curr_dot.nextElementSibling.classList.add('active');
            } else {
              slides[0].classList.add('active-slide');
              dots[0].classList.add('active');
            }

          }

          if (this.className == 'prev') {
            console.log('previous ', curr_slide);
              if (curr_slide.previousElementSibling.classList.contains('mySlides')) {
                  curr_slide.previousElementSibling.classList.add('active-slide');
                  curr_dot.previousElementSibling.classList.add('active');
                } else {
                    slides[slides.length - 1].classList.add('active-slide');
                 dots[slides.length - 1].classList.add('active');
            }

          }

        }

      }
    })();

上一个按钮导致幻灯片消失

previous button causing slideshow to disappear

html

javascript

css

slideshow