Gravity form and php

I am using gravity forms and want to populate a field with a list of my categories in a drop down. I can do it with post titles, but not with the categories This is what I have so far, any help is appreciate.

add_filter("gform_pre_render", "populate_dropdown");
add_filter("gform_admin_pre_render", "populate_dropdown");

function populate_dropdown($form){

    //only populating drop down for form id
    if($form["id"] != 4)
       return $form;

    //get categores
	global $post;
    $category = get_the_category($post->ID);

    //Creating drop down item array.
    $items = array();

    //Adding initial blank value.
    $items[] = array("text" => "", "value" => "");

    //Adding cat name to the items array
    foreach($categorys as $category)
        $items[] = array("value" => $category->cat_name, "text" => $category->cat_name);

    //number is gform field id
    foreach($form["fields"] as &$field)
        if($field["id"] == 10){
            $field["choices"] = $items;

    return $form;