这是以上答案和以上评论的组合，最终对我有效。

将插件添加到可用模板列表的功能：

function wpse255804_add_page_template ($templates) {
    $templates[\'my-custom-template.php\'] = \'My Template\';
    return $templates;
    }
add_filter (\'theme_page_templates\', \'wpse255804_add_page_template\');

function wpse255804_redirect_page_template ($template) {
    $post = get_post();
    $page_template = get_post_meta( $post->ID, \'_wp_page_template\', true );
    if (\'my-custom-template.php\' == basename ($page_template))
        $template = WP_PLUGIN_DIR . \'/mypluginname/my-custom-template.php\';
    return $template;
    }
add_filter (\'page_template\', \'wpse255804_redirect_page_template\');

谢谢你的帮助。为了使用当前的WordPress版本，我稍微修改了代码。还将其更改为支持多个自定义模板。

我打赌有更好的方法可以做到这一点，但它对我很有效。

/**
 * Load Template with Plugin
 */
function yourname_add_page_template ($templates) {
    $templates[\'page-one.php\'] = \'title here One\';
    $templates[\'page-two.php\'] = \'title here Two\';
    $templates[\'page-three.php\'] = \'title here Three\';
    return $templates;
}
add_filter (\'theme_page_templates\', \'yourname_add_page_template\');

function yourname_redirect_page_template ($template) {
    $post = get_post();
    $page_template = get_post_meta( $post->ID, \'_wp_page_template\', true );
    if (\'page-one.php\' == basename ($page_template)) {
        $template = WP_PLUGIN_DIR . \'/pluginname/templates/page-one.php\';
        return $template;
    }
    elseif (\'page-two.php\' == basename ($page_template)) {
        $template = WP_PLUGIN_DIR . \'/pluginname/templates/page-two.php\';
        return $template;
    }
    elseif (\'page-three.php\' == basename ($page_template)) {
        $template = WP_PLUGIN_DIR . \'/pluginname/templates/page-three.php\';
        return $template;
    }
}
add_filter (\'page_template\', \'yourname_redirect_page_template\');

抄本：

<?php 
   $templates = get_page_templates();
   foreach ( $templates as $template_name => $template_filename ) {
       echo "$template_name ($template_filename)<br />";
   }
?>

下面的代码片段是经过深思熟虑的，它将尝试在插件中查找模板，如果在那里找不到模板，它将尝试从主题中获取模板。

define( \'MY_PLUGIN_DIR\', plugin_dir_path( __FILE __ ) );
define( \'MY_PLUGIN_TEMPLATE_DIR\', MY_PLUGIN_DIR . \'/templates/\' );

add_filter( \'template_include\', \'ibenic_include_from_plugin\', 99 );

function ibenic_include_from_plugin( $template ) {

    $new_template = \'\';

    $provided_template_array = explode( \'/\', $template );

    // This will give us archive.php
    $new_template = end( $provided_template_array );

    // Define single and archive template for custom post type \'portfolio\'
    if( is_singular(\'portfolio\') ) {
        $new_template = \'single-portfolio.php\';
    }

    if( is_post_type_archive( \'portfolio\' ) ) {
        $new_template = \'archive-portfolio.php\';
    }

    $plugin_template = MY_PLUGIN_TEMPLATE_DIR . $new_template;

    if( file_exists( $plugin_template ) ) {
    return $plugin_template;
    }

    return $template;
}

<?php load_template( $_template_file, $require_once ) ?>