Demonstrates how to add a meta box for the built-in 'post' post type with Admin Page Framework. This is a sample plugin introduced in the tutorial Add a Meta Box for Posts (http://en.michaeluno.jp/admin-page-framework/tutorials-v3/11-add-a-meta-box-for-posts/).

tutorials-11-add-a-meta-box-for-posts.php

<?php
/*
 *  Plugin Name:    Admin Page Framework Tutorial 11 - Add a Meta Box for Posts
 *  Plugin URI:     http://en.michaeluno.jp/admin-page-framework
 *  Description:    Adds a meta box for posts.
 *  Author:         Michael Uno
 *  Author URI:     http://michaeluno.jp
 *  Version:        1.0.1
 *  Requirements:   PHP 5.2.4 or above, WordPress 3.4 or above. Admin Page Framework 3.0.6 or above
 */

// Include the library file. Set your file path here.
include( dirname( dirname( __FILE__ ) ) . '/library/apf/admin-page-framework.php' );

class APF_Tutorial_SideMetaBox extends AdminPageFramework_MetaBox {
    
    public function start() {
        
        add_action( 'the_content', array( $this, 'replyToAddContent' ) );
        
    }
        /**
         * Called when a post content is displayed.
         * 
         * @callback    filter      the_content
         * @return      string
         */
        public function replyToAddContent( $sContent ) {

            if ( ! is_singular() ) {
                return $sContent;
            }
            if ( ! is_main_query() ) {
                return $sContent;
            }
            global $post;
            if ( 'post' !== $post->post_type ) {
                return $sContent;
            }
            
            $_sMetaData = get_post_meta( $post->ID, 'tutorial_normal_metabox_text', true );
            
            return $sContent
                . '<p>Admin Page Framework Tutorial Metabox Field: ' . $_sMetaData . '</p>';
            
        }
    
    /*
     * Use the setUp() method to define settings of this meta box.
     */
    public function setUp() {
    
        /**
         * Adds setting fields in the meta box.
         */
        $this->addSettingFields(
            array(
                'field_id'          => 'tutorial_normal_metabox_text',
                'type'              => 'text',
                'title'             => __( 'Text', 'admin-page-framework-tutorial' ),
            )
        );     
    
    }
   
}

new APF_Tutorial_SideMetaBox(
    null,   // meta box ID - can be null.
    __( 'Tutorial - Add a Meta Box for Posts', 'admin-page-framework-demo' ), // title
    array( 'post' ),                               // post type slugs: post, page, etc.
    'side',                                        // context
    'low'                                          // priority
);