.net - C# FileSystemWatcher, How to know file copied completely into the watch folder

Question

I am developing a .net application, where I am using FileSystemWatcher class and attached its Created event on a folder. I have to do action on this event (i.e. copy file to some other location). When I am putting a large size into the attached watch folder the event raised immediately even the file copy process still not completed. I don’t want to check this by file.open method.

Is there any way get notify that my file copy process into the watch folder has been completed and then my event get fire.

Answer 1

It is indeed a bummer that FileSystemWatcher (and the underlying ReadDirectoryChangesW API) provide no way to get notified when a new file has been fully created.

The best and safest way around this that I've come across so far (and that doesn't rely on timers) goes like this:

Upon receiving the Created event, start a thread that, in a loop, checks whether the file is still locked (using an appropriate retry interval and maximum retry count). The only way to check if a file is locked is by trying to open it with exclusive access: If it succeeds (not throwing an IOException), then the File is done copying, and your thread can raise an appropriate event (e.g. FileCopyCompleted).