Get the current post_type context in the WordPress admin.

get_current_post_type.php

<?php
/**
 * Gets the current global post type if one is set
 */
function x_get_current_post_type() {
	global $post, $typenow, $current_screen;
	
	if( $post && $post->post_type )
		$post_type = $post->post_type;
	elseif( $typenow )
		$post_type = $typenow;
	elseif( $current_screen && $current_screen->post_type )
		$post_type = $current_screen->post_type;
	elseif( isset( $_REQUEST['post_type'] ) )
		$post_type = sanitize_key( $_REQUEST['post_type'] );
	else
		$post_type = null;
	
	return $post_type;
}