PageNavi not working

Hello Guys,

follow this tutorial to a page of my portfolio for thema, however, was only missing pagination.

Link: http://wp.tutsplus.com/tutorials/creating-a-filterable-portfolio-with-wordpress-and-jquery/

The problem is that I tried to add the plugin WP-paginavi at the end of the page and it did not work.
Actually nothing appears when I insert the code:

<? php if (function_exists ('wp_pagenavi')) {
wp_pagenavi ();
}?>

Does anyone know if missing anything else?
My files are identical to the tutorial.
Thank you!