<?php

add_filter('gform_pre_render_18', 'populate_posts');
add_filter('gform_pre_validation_18', 'populate_posts');
add_filter('gform_pre_submission_filter_18', 'populate_posts');
add_filter('gform_admin_pre_render_18', 'populate_posts');

function populate_posts($form)
{

	foreach ($form['fields'] as &$field) {
		if ($field->type != 'checkbox' || strpos($field->inputName, 'publication-list') === false) {
			continue;
		}
		
		// you can add additional parameters here to alter the posts that are retrieved
		// more info: http://codex.wordpress.org/Template_Tags/get_posts
		$brochures_query = new WP_Query(array(
			'post_type' => 'brochures',
			'posts_per_page' => -1,
			'post_status' => 'publish',
		));

		// $posts = get_posts('numberposts=-1&post_status=publish&post_type=brochures');

		$choices = array();

		foreach ($brochures_query->posts as $post) {
			$choices[] = array('text' => $post->post_title, 'value' => $post->post_title);
		}

		// update 'Select a Post' to whatever you'd like the instructive option to be
		$field->placeholder = 'Select a Post';
		$field->choices = $choices;
	}

	return $form;
}