How can I determine the copy process of a file ?

I'm using a filewatching to see if there are any changes in a certain folder. But I need to know exactly when the file is completely copied in the folder that i'm watching.

The file will be copied by an external program.

Could anyone help me out on this one ?

I tried to determine the filesize ( using the Length property ) but that gives me the size that it will take on the disk when it's completely copied...

Maybe there is a groovy way to do this, if there is please 'enlighten' me ;) .

Greetz.