How to check if the file, that i need to write to is locked, and if so
wait some time then try again?

Try to open it in a try-catch-end try block & if you get a FileIOException
then its already open

Try to open the file with 'FileShare.None' and catch the exception which is
thrown when the file is already in use.  You can use a timer control to
periodically check the file until it can be opened.

Thanks Crouchies, thanks Herfried

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