[WORDPRESS] Show all posts in a combobox

function.php

<form action="<? bloginfo('url'); ?>" method="get">
<select name="page_id" id="page_id">
<?php
global $post;
$args = array( 'numberposts' => -1);
$posts = get_posts($args);
foreach( $posts as $post ) : setup_postdata($post); ?>
        <option value="<? echo $post->ID; ?>"><?php the_title(); ?></option>
<?php endforeach; ?>
</select>
<input type="submit" name="submit" value="view" />
</form>