Get post ID in post/page edit area

Question

How can i get "post id" in post edit area for add_filter in functions.php?

I want to change file name automatically during upload. so i need to obtain post id.

the code is as follows:

add_filter( 'wp_handle_upload_prefilter', 'custom_upload_name' );   
function custom_upload_name($file)
{       
  list($name, $ext) = explode('.', $file['name']);
  $file['name'] = $post_ID.'.'.$ext;    
return $file;
}

Edited:

the final and working code:

add_filter( 'wp_handle_upload_prefilter', 'custom_upload_name' );   
function custom_upload_name($file)
{       
  $post_ID = $_POST['post_id'];   
  list($name, $ext) = explode('.', $file['name']);
  $file['name'] = $post_ID.'.'.$ext;    
return $file;
}

Answer 1

Try using $_POST['post_id'] in the upload area as file.php does not include the global $post object.

Answer 2

Did you tried using global $post object?

add_filter( 'wp_handle_upload_prefilter', 'custom_upload_name' );   

function custom_upload_name($file){ 
  global $post;      
  list($name, $ext) = explode('.', $file['name']);
  $file['name'] = $post->ID.'.'.$ext;    
return $file;
}