APP_View_Generic

class-app-view-generic.php

<?php

/**
 * Helper class for using the generic.php template from a plugin.
 *
 * Optional methods:
 *  - init() - for registering post types, taxonomies, rewrite rules etc.
 *  - before_load_template() - for processing forms, enqueueing scripts etc
 */
abstract class APP_View_Generic {

	/**
	 * Test if this controller should handle the current page.
	 *
	 * Use is_*() conditional tags and get_query_var()
	 *
	 * @return bool
	 */
	abstract function condition();

	/**
	 * Use this to actually display something within generic.php
	 *
	 * Can be another call to locate_template()
	 */
	abstract function load_template();

	function __construct() {
		if ( method_exists( $this, 'init' ) )
			add_action( 'init', array( $this, 'init' ) );

		add_action( 'template_redirect', array( $this, '_template_redirect' ) );
	}

	final function _template_redirect() {
		if ( !$this->condition() )
			return;

		if ( method_exists( $this, 'before_load_template' ) )
			$this->before_load_template();

		add_action( 'generic_content', array( $this, 'load_template' ) );

		locate_template( 'generic.php', true );
		die;
	}
}

generic-view-example.php

<?php

class My_Generic_View extends APP_View_Generic {

	function init() {
		global $wp;

		$wp->add_query_var( 'my_plugin_query_var' );
	}

	function condition() {
		return get_query_var( 'my_plugin_query_var' );
	}

	function load_template() {
		echo '<p>In the generic.php template.</p>';
	}
}

new My_Generic_View;

Context: http://core.trac.wordpress.org/ticket/20509

Similar: https://gist.github.com/2865132