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

Use the System.IO.FileSystemWatcher to determine files that are changed.

Open them in an exclusive reader (FileMode.Read) in make the copies, and catch the exception should this fail (because someone else has it open for writing).