How to test if a file is currently being written to

Question

I have an application that must check a folder and read any files that are copied into it. How do I test if a file in that folder is currently being written to? I only want

Answer 1

When you open it with System.IO.File.OpenWrite(filename), it should throw IOException.

So, in a try catch, the code being executed in the catch block should tell you the file was open.