我正在尝试使用复制目录WP_Filesystem API 使用该方法copy_dir() 关于插件激活，但它是给我以下错误消息：

Plugin could not be activated because it triggered a fatal error.

Fatal error: Call to undefined method WP_Filesystem_Direct::copy_dir()
in D:\\xampp\\htdocs\\wordpress\\wp-content\\plugins\\xxxxxxxx\\xxxxxx.php on line 98

Here is my codes:

function sstssfb_activation_hook_vcheck() {
    delete_option(esc_attr("sstssfb_stop_showingvchecknotice"));

    /* INITIALIZE WPFilesytem */
    $access_type = get_filesystem_method();
    if($access_type === \'direct\') {
        $url = \'http://\'.$_SERVER[\'HTTP_HOST\'].$_SERVER[\'REQUEST_URI\'];
        $creds = request_filesystem_credentials($url, \'\', false, false, array());
            // initialize the API
            if ( ! WP_Filesystem($creds) ) {
                // any problems and we exit
                return;
            }
            global $wp_filesystem;
    /* CREATE SSTSSFB_ASSETS DIRECTORY */
        if(!$wp_filesystem->is_dir(SSTSSFB_ASSET_DIR)) 
        {
            $wp_filesystem->mkdir(SSTSSFB_ASSET_DIR);
        }

    /* MOVE ADDITIONAL assets TO THAT (sstssfb_assets) DIRECTORY */
        // addons
        if(file_exists(SSTSSFBDIR_ADDONS_ORI))
        $wp_filesystem->copy_dir(SSTSSFBDIR_ADDONS_ORI, SSTSSFB_ASSET_DIR, true);
        $wp_filesystem->delete(SSTSSFBDIR_ADDONS_ORI);
        // themes
        if(file_exists(SSTSSFB_THEMEDIR_ORI))
        $wp_filesystem->copy_dir(SSTSSFB_THEMEDIR_ORI, SSTSSFB_ASSET_DIR, true);
        $wp_filesystem->delete(SSTSSFBDIR_ADDONS_ORI);
    }

    }
    register_activation_hook(__FILE__, "sstssfb_activation_hook_vcheck");