In event receivers other than
ItemAdding it is a simple task to determine if the current item is a file or a folder. You would write something along the lines of:
bool isFile = (properties.ListItem.File != null);
However in the
properties.ListItem is null. This is because the list item is yet to be created. In order to determine if the current item is a file, you should instead try this:
bool isFile = (properties.AfterProperties["vti_filesize"] != null);
You are welcome!