Limit metabox by page template

gistfile1.aw

Limit Metabox by Page Template
To test, go into init.php and replace the add() function with the one below. Then, add the following to a metabox array:

'show_on' => array( 'key' => 'page-template', 'value' => 'template-name.php' ),

Of course, replacing template-name.php with your template's file name.

<?php

	// Add metaboxes
	function add() {
		$this->_meta_box['context'] = empty($this->_meta_box['context']) ? 'normal' : $this->_meta_box['context'];
		$this->_meta_box['priority'] = empty($this->_meta_box['priority']) ? 'high' : $this->_meta_box['priority'];
		foreach ( $this->_meta_box['pages'] as $page ) {
			if( !isset( $this->_meta_box['show_on'] ) ) {
				add_meta_box( $this->_meta_box['id'], $this->_meta_box['title'], array(&$this, 'show'), $page, $this->_meta_box['context'], $this->_meta_box['priority']) ;
			} else {
				if ( 'id' == $this->_meta_box['show_on']['key'] ) {

					// If we're showing it based on ID, get the current ID					
					if( isset( $_GET['post'] ) ) $post_id = $_GET['post'];
					elseif( isset( $_POST['post_ID'] ) ) $post_id = $_POST['post_ID'];

					// If current page id is in the included array, display the metabox
					if ( isset( $post_id) && in_array( $post_id, $this->_meta_box['show_on']['value'] ) )
						add_meta_box( $this->_meta_box['id'], $this->_meta_box['title'], array(&$this, 'show'), $page, $this->_meta_box['context'], $this->_meta_box['priority']) ;
						
				} elseif( 'page-template' == $this->_meta_box['show_on']['key'] )  {

					// Get the current ID
					if( isset( $_GET['post'] ) ) $post_id = $_GET['post'];
					elseif( isset( $_POST['post_ID'] ) ) $post_id = $_POST['post_ID'];
					if( !( isset( $post_id ) || is_page() ) ) return;
					
					// Get current template
					$current_template = get_post_meta( $post_id, '_wp_page_template', true );
					
					// See if there's a match
					if( $current_template == $this->_meta_box['show_on']['value'] )
						add_meta_box( $this->_meta_box['id'], $this->_meta_box['title'], array(&$this, 'show'), $page, $this->_meta_box['context'], $this->_meta_box['priority']) ;
				}
			}
		}
	}

It's working just fine on the client project I'm working on, but I'd like a bit more testing before I add it to core.

Added line 33 to make sure we have an ID and are on a post.