我的目标是延迟加载缩略图。如中所示here, 我需要添加class="lazy", 占位符必须位于src 和延迟加载的图像data-original.

此代码工作正常：

if ( has_post_thumbnail() ) { 
    $size = \'attachment-thumbnail-400-300\';

    //Get thumbnail source
    $thumb = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), \'thumbnail-400-300\' );
    $src = $thumb[\'0\'];

    $placeholder = "//placehold.it/400x300/eee/222/&text=+";

    $default_attr = array(
        \'src\' => $placeholder,
        \'data-original\' => $src,
        \'class\' => "lazy $size",
    );
    the_post_thumbnail(\'thumbnail-400-300\', $default_attr);
}   

默认情况下，这将获取源和所有内容：

the_post_thumbnail(\'thumbnail-400-300\'); 

我试图用多种不同的方式修改代码，但我只能用以下方法：

 $thumb = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), \'thumbnail-400-300\' );
 $src = $thumb[\'0\'];

这似乎是我不需要的额外请求（我需要加载很多缩略图）。如何修改我的代码以获取src 直接使用the_post_thumbnail 并将其指定为data-original?

if ( has_post_thumbnail() ) { 
   $class = \'lazy attachment-thumbnail-400-300\';

   //Get thumbnail source
   $thumb = wp_get_attachment_image_src(get_post_thumbnail_id($post->ID), \'thumbnail-400-300\');
   $src = $thumb[\'0\'];

   $placeholder = "//placehold.it/400x300/eee/222/&text=+";

   echo \'<img src="\'.$placeholder.\'" data-original="\'.$src.\'" class="\'.$class.\'" />\';
}

$size = \'attachment-thumbnail-400-300\';
$placeholder = \'src="//placehold.it/400x300/eee/222/&text=\'.urlencode(\'+\').\'"\';
$pattern = \'/src\\s*=\\s*"(.+?)"/\'; 

$thumb = get_the_post_thumbnail($post->ID , \'thumbnail-400-300\'); 

preg_match($pattern, $thumb, $matches, PREG_OFFSET_CAPTURE);

if ( ! empty($matches) ){

    $src = $matches[0][0];

    $thumb = str_replace( $src, $placeholder, $thumb );

    $thumb = str_replace( \'class="\', \'class="\' . "lazy $size ", $thumb );

    $data_original = str_replace( \'src="\', \'data-original="\', $src );

    $thumb = str_replace( \' src="\', $data_original . \' src="\', $thumb );
}

echo $thumb;