解决 WordPress 4.9 页面模板功能无法正常使用

WordPress 4.9.1 及以上版本已经默认修复该问题，建议直接更新到最新版本，无需再看本文下面的内容了！

WordPress 4.9 有一个重要更新是：在WP后台编辑主题和插件文件时，支持按层级显示所有文件。为了性能考虑，使用了 transient 缓存机制。但是却没有提供任何手动清除缓存的功能，导致有些用户升级到 WordPress 4.9 以后，发现“页面属性 – 模板”这个功能不能正常使用了，不显示主题自带的模板文件！

要解决这个问题，我们可以添加下面的代码到当前主题的 functions.php 就可以了：

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/**
 * Plugin name: WP Trac #42573: Fix for theme template file caching.
 * Description: Flush the theme file cache each time the admin screens are loaded which uses the file list.
 * Plugin URI: https://core.trac.wordpress.org/ticket/42573
 * Author: Weston Ruter, XWP.
 * Author URI: https://weston.ruter.net
 */
function wp_42573_fix_template_caching( WP_Screen $current_screen ) {
	// Only flush the file cache with each request to post list table, edit post screen, or theme editor.
	if ( ! in_array( $current_screen->base, array( 'post', 'edit', 'theme-editor' ), true ) ) {
		return;
	}
	$theme = wp_get_theme();
	if ( ! $theme ) {
		return;
	}
	$cache_hash = md5( $theme->get_theme_root() . '/' . $theme->get_stylesheet() );
	$label = sanitize_key( 'files_' . $cache_hash . '-' . $theme->get( 'Version' ) );
	$transient_key = substr( $label, 0, 29 ) . md5( $label );
	delete_transient( $transient_key );
}
add_action( 'current_screen', 'wp_42573_fix_template_caching' );

/**
* Plugin name: WP Trac #42573: Fix for theme template file caching.
* Description: Flush the theme file cache each time the admin screens are loaded which uses the file list.
* Plugin URI: https://core.trac.wordpress.org/ticket/42573
* Author: Weston Ruter, XWP.
* Author URI: https://weston.ruter.net
*/
function wp_42573_fix_template_caching( WP_Screen $current_screen ) {
// Only flush the file cache with each request to post list table, edit post screen, or theme editor.
if ( ! in_array( $current_screen->base, array( ‘post’, ‘edit’, ‘theme-editor’ ), true ) ) {
return;
}
$theme = wp_get_theme();
if ( ! $theme ) {
return;
}
$cache_hash = md5( $theme->get_theme_root() . ‘/’ . $theme->get_stylesheet() );
$label = sanitize_key( ‘files_’ . $cache_hash . ‘-‘ . $theme->get( ‘Version’ ) );
$transient_key = substr( $label, 0, 29 ) . md5( $label );
delete_transient( $transient_key );
}
add_action( ‘current_screen’, ‘wp_42573_fix_template_caching’ );

如果你不想编辑代码，点击下载此插件安装启用即可：wp-42573