タクソノミー・カスタム投稿タイプごとに、管理画面から１ページ当たりの表示件数を変更するプラグイン。

custom-ppp.php

<?php
/*
Plugin Name: Custom PPP
Plugin URI:
Description: Posts per page for Custom Post Type and Taxonomy
Version: 0.6
Author: Toro_Unit
Author URI: http://www.torounit.com
License: GPL2 or Later
*/



/**
 *
 * Custom_PPP
 * @package Custom_PPP
 * @version 0.6
 *
 */

Class Custom_PPP {

	private $posts_per_page;

	public function __construct () {
		$this->posts_per_page = get_option( "posts_per_page" );
		$this->add_hooks();
		register_uninstall_hook( __FILE__, array( __CLASS__, 'uninstall_hook') );
	}

	public function add_hooks() {
		add_action( "pre_get_posts", array($this,"pre_get_posts"));
		add_action("admin_init", array($this,"update_option"), 10);
		add_action("admin_init", array($this,"add_settings_fields"), 11);
	}

	private static function get_post_types() {
		return get_post_types( array('_builtin'=>false, 'publicly_queryable'=>true, 'show_ui' => true), "objects");
	}

	private static function get_taxonomies() {
		return get_taxonomies( array( "public" => true ), "objects");
	}


	public function pre_get_posts( $query ) {
		if($query->is_main_query() and !is_admin()) {
			foreach (self::get_post_types() as $post_type) {
				if($query->is_post_type_archive( $post_type->name )) {
					$query->set("posts_per_page", get_option( "posts_per_page_of_cpt_".$post_type->name, $this->posts_per_page));
					return;
				}
			}

			foreach (self::get_taxonomies() as $taxonomy) {
				if($query->is_tax( $taxonomy->name )) {
					$query->set("posts_per_page", get_option( "posts_per_page_of_tax_".$taxonomy->name, $this->posts_per_page));
					return;
				}
			}
		}
	}


	public function update_option() {
		if(isset($_POST['submit']) && isset($_POST['_wp_http_referer']) && strpos($_POST['_wp_http_referer'],'options-reading.php') !== FALSE ) {

			foreach (self::get_post_types() as $post_type) {
				if($_POST["posts_per_page_of_cpt_".$post_type->name]) {
					update_option("posts_per_page_of_cpt_".$post_type->name, $_POST["posts_per_page_of_cpt_".$post_type->name]);
				}
			}

			foreach (self::get_taxonomies() as $taxonomy) {
				if($_POST["posts_per_page_of_tax_".$taxonomy->name]) {
					update_option("posts_per_page_of_tax_".$taxonomy->name, $_POST["posts_per_page_of_tax_".$taxonomy->name]);
				}
			}
		}
	}


	public function add_settings_fields() {
		foreach (self::get_post_types() as $post_type) {
			$this->add_settings_field("posts_per_page_of_cpt_".$post_type->name, $post_type, "post_type");
		}
		foreach (self::get_taxonomies() as $taxonomy) {
			$this->add_settings_field("posts_per_page_of_tax_".$taxonomy->name, $taxonomy, "taxonomy");
		}
	}

	public function add_settings_field( $id, $obj, $type ) {
			add_settings_field( $id, $obj->label, array($this, "create_field"), "reading", 'default', array("label_for" => $id, "obj" => $obj ,"type" => $type));
	}

	public function create_field( $arg ) {
		$obj = $arg["obj"];

		$field = $arg["label_for"];
		?>
		<input name="<?php echo $field;?>" type="number" step="1" min="-1" id="<?php echo $field;?>" value="<?php form_option( $field ); ?>" class="small-text" /> <?php _e( 'posts' ); ?>
		<?php
	}


	public static function uninstall_hook() {
		foreach (self::get_post_types() as $post_type) {
			delete_option("posts_per_page_of_cpt_".$post_type->name);
		}

		foreach (self::get_taxonomies() as $taxonomy) {
			delete_option("posts_per_page_of_tax_".$taxonomy->name);
		}
	}

}

new Custom_PPP();