the_post_thumbnail
the_post_thumbnail 在 WordPress 中主要用来打印文章中设定的缩略图，而 get_the_post_thumbnail 函数可以将你需要的 HTML 代码以字符串的形式返回。
the_post_thumbnail 函数的使用
the_post_thumbnail( $size , $attr)
函数参数
the_post_thumbnail 函数声明
/**
* Display Post Thumbnail.
*
* @since 2.9.0
*
* @param int $size Optional. Image size. Defaults to 'post-thumbnail', which theme sets using set_post_thumbnail_size( $width, $height, $crop_flag );.
* @param string|array $attr Optional. Query string or array of attributes.
*/
function the_post_thumbnail( $size = 'post-thumbnail', $attr = '' ) {
echo get_the_post_thumbnail( null, $size, $attr );
}
get_the_post_thumbnail 函数声明
* Retrieve Post Thumbnail.
*
* @since 2.9.0
*
* @param int $post_id Optional. Post ID.
* @param string $size Optional. Image size. Defaults to 'post-thumbnail'.
* @param string|array $attr Optional. Query string or array of attributes.
*/
function get_the_post_thumbnail( $post_id = null, $size = 'post-thumbnail', $attr = '' ) {
$post_id = ( null === $post_id ) ? get_the_ID() : $post_id;
$post_thumbnail_id = get_post_thumbnail_id( $post_id );
$size = apply_filters( 'post_thumbnail_size', $size );
if ( $post_thumbnail_id ) {
do_action( 'begin_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size ); // for "Just In Time" filtering of all of wp_get_attachment_image()'s filters
if ( in_the_loop() )
update_post_thumbnail_cache();
$html = wp_get_attachment_image( $post_thumbnail_id, $size, false, $attr );
do_action( 'end_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size );
} else {
$html = '';
}
return apply_filters( 'post_thumbnail_html', $html, $post_id, $post_thumbnail_id, $size, $attr );
set_post_thumbnail_size
set_post_thumbnail_size 函数是 WordPress 中设置特色图像大小的一个函数也是 add_image_size 函数的一个简单的应用。为了更好的突出特色图像的使用， WordPress 自 2.9.0 版开始，便有了本函数。
set_post_thumbnail_size 函数的使用
与 add_image_size 函数使用大概类似，只是该函数只针对特色图像进行设置。
set_post_thumbnail_size( $width, $height, $crop)
参数详解
实例
set_post_thumbnail_size(100,0,true);
注意：当高度和宽度任意一个为0时， WP 将自动适应另一个值进行缩略图生成工作。
函数声明
/**
* Registers an image size for the post thumbnail
*
* @since 2.9.0
*/
function set_post_thumbnail_size( $width = 0, $height = 0, $crop = false ) {
add_image_size( 'post-thumbnail', $width, $height, $crop );
