Bootstrap 4：轮播淡入淡出过渡不起作用

Question

下面的代码在我使用 Bootstrap 版本 3 时工作得非常好。但是，自从升级到 Bootstrap 4 Beta2 后，淡入淡出过渡不起作用。它只是跳转到下一个图像而不是平滑过渡：

HTML

<div id="carousel1" class="carousel fade" data-ride="carousel">
    <ol class="carousel-indicators">
      <li data-target="#carousel1" data-slide-to="0" class="active"></li>
      <li data-target="#carousel1" data-slide-to="1"></li>
      <li data-target="#carousel1" data-slide-to="2"></li>
    </ol>

    <div class="carousel-inner" role="listbox">
      <div class="item active"><img src="images/a.jpg" alt="First slide image" class="center-block">
        <div class="carousel-caption">
          <h3>First slide Heading</h3>
          <p>First slide Caption</p>
        </div>
      </div>
      <div class="item"><img src="images/b.jpg" alt="Second slide image" class="center-block">
        <div class="carousel-caption">
          <h3>Second slide Heading</h3>
          <p>Second slide Caption</p>
        </div>
      </div>
      <div class="item"><img src="images/c.jpg" alt="Third slide image" class="center-block">
        <div class="carousel-caption">
          <h3>Third slide Heading</h3>
          <p>Third slide Caption</p>
        </div>
      </div>
    </div>

    <a class="left carousel-control" href="#carousel1" role="button" data-slide="prev">
      <span class="glyphicon glyphicon-chevron-left" aria-hidden="true"></span>
      <span class="sr-only">Previous</span>
    </a>
    <a class="right carousel-control" href="#carousel1" role="button" data-slide="next">
      <span class="glyphicon glyphicon-chevron-right" aria-hidden="true"></span>
      <span class="sr-only">Next</span>
    </a>
</div>

CSS

.carousel.fade {
     opacity: 1;
}
.carousel.fade .item {
    transition: opacity ease-out .7s;
    left: 0;
    opacity: 0; /* hide all slides */
    top: 0;
    position: absolute;
    width: 100%;
    display: block;
}
.carousel.fade .item:first-child {
    top: auto;
    opacity: 1; /* show first slide */
    position: relative;
}
.carousel.fade .item.active {
    opacity: 1;
}

JS

$(function(){
    $('.carousel').carousel({
      interval: 6000
    });
});

环顾四周，似乎最近的引导升级存在一些问题，我们将不胜感激。

Answer 1

正如您已经注意到的那样，Bootstrap 4 中发生了很多变化。让我带您了解一下我在下面的解决方案中采用的方法。

• .fade 已重命名为 .carousel-fade 以不干扰默认 Bootstrap .fade 类。
• .item 已重命名为 .carousel-item，因为这是 Bootsrap 4 中轮播项目的名称。
• 由于渐变效果，现在幻灯片的定位是绝对的，我将.embed-responsive embed-responsive-16by9 类添加到.carousel-inner 以及.embed-responsive-item 到.carousel-item 以保持幻灯片容器的高度并注意幻灯片项目的定位。 （如果您想使用具有其他纵横比的图像，您应该更改.embed-responsive-16by9 类。默认值列在here。）

所以这就是我的方法：

.carousel.carousel-fade .carousel-item {
    display: block;
    opacity: 0;
    transition: opacity ease-out .7s;
}

.carousel.carousel-fade .carousel-item.active {
    opacity: 1 !important;
}

<div id="carousel-fade" class="carousel carousel-fade" data-ride="carousel" data-interval="2000">
    <ol class="carousel-indicators">
        <li data-target="#carousel-fade" data-slide-to="0" class="active"></li>
        <li data-target="#carousel-fade" data-slide-to="1"></li>
        <li data-target="#carousel-fade" data-slide-to="2"></li>
    </ol>

    <div class="carousel-inner embed-responsive embed-responsive-16by9" role="listbox">
      <div class="carousel-item embed-responsive-item active">
        <img src="http://via.placeholder.com/1600x900/483D8B/ffffff?text=Slide%201" alt="First slide image" class="img-fluid">
        <div class="carousel-caption">
          <h3>First slide Heading</h3>
          <p>First slide Caption</p>
        </div>
      </div>

      <div class="carousel-item embed-responsive-item">
        <img src="http://via.placeholder.com/1600x900/9400D3/ffffff?text=Slide%202" alt="Second slide image" class="img-fluid">
        <div class="carousel-caption">
          <h3>Second slide Heading</h3>
          <p>Second slide Caption</p>
        </div>
      </div>

      <div class="carousel-item embed-responsive-item">
        <img src="http://via.placeholder.com/1600x900/FF1493/ffffff?text=Slide%203" alt="Third slide image" class="img-fluid">
        <div class="carousel-caption">
          <h3>Third slide Heading</h3>
          <p>Third slide Caption</p>
        </div>
      </div>
    </div>

    <a class="carousel-control-prev" href="#carousel-fade" role="button" data-slide="prev">
        <span class="carousel-control-prev-icon" aria-hidden="true"></span>
        <span class="sr-only">Previous</span>
    </a>
    <a class="carousel-control-next" href="#carousel-fade" role="button" data-slide="next">
        <span class="carousel-control-next-icon" aria-hidden="true"></span>
        <span class="sr-only">Next</span>
    </a>
</div>


<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.3/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/js/bootstrap.min.js"></script>

还有两个注意事项：

• 您还可以通过.carousel 的data-interval 属性设置更改间隔。
• Bootstrap 4 中轮播控件的标记也已更改。