Get the current post_type context in the WordPress admin.

get_current_post_type.php

<?php
/**
 * gets the current post type in the WordPress Admin
 */
function get_current_post_type() {
  global $post, $typenow, $current_screen;

  //we have a post so we can just get the post type from that
  if ( $post && $post->post_type ) {
    return $post->post_type;
  }

  //check the global $typenow - set in admin.php
  elseif ( $typenow ) {
    return $typenow;
  }

  //check the global $current_screen object - set in sceen.php
  elseif ( $current_screen && $current_screen->post_type ) {
    return $current_screen->post_type;
  }

  //check the post_type querystring
  elseif ( isset( $_REQUEST['post_type'] ) ) {
    return sanitize_key( $_REQUEST['post_type'] );
  }

  //lastly check if post ID is in query string
  elseif ( isset( $_REQUEST['post'] ) ) {
    return get_post_type( $_REQUEST['post'] );
  }

  //we do not know the post type!
  return null;
}