settings.php

<?php
if(!class_exists('WP_CCSVE_Settings'))
{
	class WP_CCSVE_Settings
	{
		/**
		 * Construct the plugin object
		 */
		public function __construct()
		{
			// register actions
            add_action('admin_init', array(&$this, 'admin_init'));
        	add_action('admin_menu', array(&$this, 'add_menu'));
		} // END public function __construct
		
        /**
         * hook into WP's admin_init action hook
         */
        public function admin_init()
        {
        	register_setting('wp_ccsve-group', 'ccsve_post_type');
        	register_setting('wp_ccsve-group', 'ccsve_custom_fields');

        	add_settings_section(
        	    'wp_ccsve_template-section', 
        	    'Custom CSV Export Settings', 
        	    array(&$this, 'settings_section_wp_ccsve_template'), 
        	    'wp_ccsve_template'
        	);
        	
            add_settings_field(
                'ccsve_post_type', 
                'Custom Post Type to Export', 
                array(&$this, 'settings_field_select_post_type'), 
                'wp_ccsve_template', 
                'wp_ccsve_template-section'
                
            );
            add_settings_field(
                'ccsve_custom_fields', 
                'Custom Fields to Export', 
                array(&$this, 'settings_field_select_custom_fields'), 
                'wp_ccsve_template', 
                'wp_ccsve_template-section'
            );
           
        } // END public static function activate
        
        public function settings_section_wp_ccsve_template()
        {
            
            echo 'These are the settings for the Custom CSV Export Plugin.';
        }
        
        /**
         * This function provides text inputs for settings fields
         */
        public function settings_field_select_post_type()
        {
        
        	$args=array(
        		'public'   => true,
  			);
            // Get the field name from the $args array
            $items = get_post_types($args);
            // Get the value of this setting
            $options = get_option('ccsve_post_type');
            // echo a proper input type="text"
            foreach ($items as $item) {
             	$checked = ($options==$item) ? ' checked="checked" ' : '';
             	echo '<input type="radio" id="post_type"'.$item.' name="ccsve_post_type" value="'.$item.'" '.$checked.'" />';
             	echo '<label for=post_type'.$item.'> '.$item.'</label>';
             	echo ' <br />';
            }
        } // END public function settings_field_input_text($args)
        
        public function settings_field_select_custom_fields()
        {
        	$ccsve_post_type = get_option('ccsve_post_type');
        	$meta_keys = get_post_meta_keys($ccsve_post_type);
            $ccsve_custom_fields =get_option('ccsve_custom_fields');
            $ccsve_meta_keys_num = count($meta_keys);
            echo '<select multiple="multiple" size="'.$ccsve_meta_keys_num.'" name="ccsve_custom_fields[selectinput][]">';
            foreach ($meta_keys as $meta_key) {
            	if (in_array($meta_key, $ccsve_custom_fields['selectinput'])){
            	 echo '\n\t<option selected="selected" value="'. $meta_key . '">'.$meta_key.'</option>'; 
            	} else {
            	 echo '\n\t\<option value="'.$meta_key .'">'.$meta_key.'</option>'; }
        } // END public function settings_field_input_text($args)
        
        /**
         * add a menu
         */		
        }
        public function add_menu()
        {
            // Add a page to manage this plugin's settings
        	add_options_page(
        	    'CCSVE Settings', 
        	    'Custom CSV', 
        	    'manage_options', 
        	    'wp_ccsve_template', 
        	    array(&$this, 'plugin_settings_page')
        	);
        } // END public function add_menu()
    
        /**
         * Menu Callback
         */		
        public function plugin_settings_page()
        {
        	if(!current_user_can('manage_options'))
        	{
        		wp_die(__('You do not have sufficient permissions to access this page.'));
        	}
	
        	// Render the settings template
        	include(sprintf("%s/templates/settings.php", dirname(__FILE__)));
        } // END public function plugin_settings_page()
    } // END class wp_ccsve_template_Settings
} // END if(!class_exists('wp_ccsve_template_Settings'))

function generate_post_meta_keys($post_type){
global $wpdb;
    $query = "
        SELECT DISTINCT($wpdb->postmeta.meta_key) 
        FROM $wpdb->posts 
        LEFT JOIN $wpdb->postmeta 
        ON $wpdb->posts.ID = $wpdb->postmeta.post_id 
        WHERE $wpdb->posts.post_type = '%s' 
        AND $wpdb->postmeta.meta_key != '' 
        AND $wpdb->postmeta.meta_key NOT RegExp '(^[_0-9].+$)' 
        AND $wpdb->postmeta.meta_key NOT RegExp '(^[0-9]+$)'
    ";
    $meta_keys = $wpdb->get_col($wpdb->prepare($query, $post_type));
    set_transient($post_type.'post_meta_keys', $meta_keys, 60*60*24); # 1 Day Expiration
    return $meta_keys;
}

function get_post_meta_keys($post_type){
    $cache = get_transient($post_type.'post_meta_keys');
    $meta_keys = $cache ? $cache : generate_post_meta_keys($post_type);
    return $meta_keys;
}

function ccsve_checkboxes_fix($input) {

   $options = get_option('ccsve_custom_fields');
   $merged = $options;
   $merged[] = $input;
}