@karim79 has the right answer, but I had to rewrite his example to suit my purposes. His example assumes that the name of the submitted field is known and can be hard coded in. I took that a step further and made a function that will tell me if any files were uploaded without having to know the name of the upload field.
/**
* Tests all upload fields to determine whether any files were submitted.
*
* @return boolean
*/
function files_uploaded() {
// bail if there were no upload forms
if(empty($_FILES))
return false;
// check for uploaded files
$files = $_FILES['files']['tmp_name'];
foreach( $files as $field_title => $temp_name ){
if( !empty($temp_name) && is_uploaded_file( $temp_name )){
// found one!
return true;
}
}
// return false if no files were found
return false;
}