延迟加载在引导轮播中不起作用

dm4web的答案不考虑通过直接单击轮播指示器跳过幻灯片。无论您如何滑动，此版本都可以正确加载图像，使用 Bootstrap 的event.relatedTarget（正在滑入到位的项目，请参阅官方文档）。尝试运行下面的代码片段并单击指示器以向前切换几张幻灯片。

var cHeight = 0;
$('#carousel-example-generic').on('slide.bs.carousel', function(e) {
  var $nextImage = $(e.relatedTarget).find('img');
  $activeItem = $('.active.item', this);
  // prevents the slide decrease in height
  if (cHeight == 0) {
    cHeight = $(this).height();
    $activeItem.next('.item').height(cHeight);
  }
  // prevents the loaded image if it is already loaded
  var src = $nextImage.data('lazy-load-src');
  if (typeof src !== "undefined" && src != "") {
    $nextImage.attr('src', src)
    $nextImage.data('lazy-load-src', '');
  }
});

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<div class="container-fluid">
  <div id="carousel-example-generic" class="carousel slide" data-ride="carousel">
    <!-- Indicators -->
    <ol class="carousel-indicators">
      <li data-target="#carousel-example-generic" data-slide-to="0" class="active"></li>
      <li data-target="#carousel-example-generic" data-slide-to="1"></li>
      <li data-target="#carousel-example-generic" data-slide-to="2"></li>
      <li data-target="#carousel-example-generic" data-slide-to="3"></li>
      <li data-target="#carousel-example-generic" data-slide-to="4"></li>
    </ol>
    <!-- Wrapper for slides -->
    <div class="carousel-inner" role="listbox">
      <div class="item active">
        <img src="http://placehold.it/5000x1000">
      </div>
      <div class="item">
        <img data-lazy-load-src="http://placehold.it/5001x1000">
      </div>
      <div class="item">
        <img data-lazy-load-src="http://placehold.it/5002x1000">
      </div>
      <div class="item">
        <img data-lazy-load-src="http://placehold.it/5003x1000">
      </div>
      <div class="item">
        <img data-lazy-load-src="http://placehold.it/5004x1000">
      </div>
    </div>
    <!-- Controls -->
    <a class="left carousel-control" href="#carousel-example-generic" 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="#carousel-example-generic" role="button" data-slide="next">
      <span class="glyphicon glyphicon-chevron-right" aria-hidden="true"></span>
      <span class="sr-only">Next</span>
    </a>
  </div>
</div>

http://jsfiddle.net/ys4je40u/

1. 将类添加到项对象lazy-load
2. 使用slide.bs.carousel事件

.CSS：

.lazy-load {
    background: url("http://www.mozart.it/images/preloader.gif") center center no-repeat;
}

JQ：

var cHeight = 0;
$('#myCarousel').on('slide.bs.carousel', function (e) {
    var $nextImage = null;
    $activeItem = $('.active.item', this);
    if (e.direction == 'left'){
        $nextImage = $activeItem.next('.item').find('img');
    } else {
        if ($activeItem.index() == 0){
            $nextImage = $('img:last', $activeItem.parent());
        } else {
            $nextImage = $activeItem.prev('.item').find('img');
        }
    }
    // prevents the slide decrease in height
    if (cHeight == 0) {
       cHeight = $(this).height();
       $activeItem.next('.item').height(cHeight);
    }
    // prevents the loaded image if it is already loaded
    var src = $nextImage.data('lazy-load-src');
    if (typeof src !== "undefined" && src != "") {
       $nextImage.attr('src', src)
       $nextImage.data('lazy-load-src', '');
    }
});

如果您的幻灯片中有多个图像，则必须使用以下内容：

var cHeight = 0;
$('#carousel').on('slide.bs.carousel', function (e) {
    var $nextImage = null;
    $activeItem = $('.active.item', this);
    if (e.direction == 'left'){
        $nextImage = $activeItem.next('.item').find('img');
    } else {
        if ($activeItem.index() == 0){
            $nextImage = $('img:last', $activeItem.parent());
        } else {
            $nextImage = $activeItem.prev('.item').find('img');
        }
    }
    // prevents the slide decrease in height
    if (cHeight == 0) {
       cHeight = $(this).height();
       $activeItem.next('.item').height(cHeight);
    }
    // => Changes here ! 
    // prevents the loaded images if it is already loaded
    $nextImage.each(function(){
        var $this = $(this),
            src = $this.data('original');
        if (typeof src !== "undefined" && src != "") {
           $this.attr('src', src)
           $this.data('original', '');
        }
    });
});

几个月前创建了这个"有点通用"的解决方案，到目前为止没有任何问题......

var $ajaxCarousel = $('.carousel-ajax');
if ($ajaxCarousel.length > 0) {
    $ajaxCarousel.on('slide.bs.carousel', function (e) {
        var $upcomingImage = $(e.relatedTarget).find('img');
        if (typeof $upcomingImage.attr('src') === 'undefined') {
            $upcomingImage.attr('src', $upcomingImage.data('src'));
        }
    });
    // preload first image
    $ajaxCarousel.each(function() {
        var $firstImage = $(this).find('[data-slide-number=0]').find('img');
        $firstImage.attr('src', $firstImage.data('src'));
    });
}

在HTML中，您所要做的就是将"carousel-ajax"类添加到现有的轮播中，并在img的src标签前面加上"data-"：

<img data-src="..." />