how can you easily check if access is denied for a file in .NET?

Question

Basically, I would like to check if I have rights to open the file before I actually try to open it; I do not want to use a try/catch for this check unless I have to. Is the

Answer 1

Quick tip for anyone else coming here with a similar problem:

Watch out for web synchronization apps such as DropBox. I just spent 2 hours thinking the "using" statement (Dispose pattern) is broken in .NET.

I eventually realised that Dropbox is continually reading and writing files in the background, in order to sync them.

Guess where my Visual Studio Projects folder is located? Inside the "My Dropbox" folder of course.

Therefore as I ran my application in Debug mode, the files it was reading and writing were also continually being accessed by DropBox to be synched with the DropBox server. This caused the locking/access conflicts.

So at least I now know that I need to a more robust File Open function (ie TryOpen() that will make multiple attempts). I am surprised it's not already a built-in part of the framework.

[Update]

Here's my helper function:

/// 

/// Tries to open a file, with a user defined number of attempt and Sleep delay between attempts.
/// 
/// The full file path to be opened
/// Required file mode enum value(see MSDN documentation)
/// Required file access enum value(see MSDN documentation)
/// Required file share enum value(see MSDN documentation)
/// The total number of attempts to make (multiply by attemptWaitMS for the maximum time the function with Try opening the file)
/// The delay in Milliseconds between each attempt.
/// A valid FileStream object for the opened file, or null if the File could not be opened after the required attempts
public FileStream TryOpen(string filePath, FileMode fileMode, FileAccess fileAccess,FileShare fileShare,int maximumAttempts,int attemptWaitMS)
{
    FileStream fs = null;
    int attempts = 0;

    // Loop allow multiple attempts
    while (true)
    {
        try
        {
            fs = File.Open(filePath, fileMode, fileAccess, fileShare);

            //If we get here, the File.Open succeeded, so break out of the loop and return the FileStream
            break;
        }
        catch (IOException ioEx)
        {
            // IOExcception is thrown if the file is in use by another process.

            // Check the numbere of attempts to ensure no infinite loop
            attempts++;
            if (attempts > maximumAttempts)
            {
                // Too many attempts,cannot Open File, break and return null 
                fs = null;
                break;
            }
            else
            {
                // Sleep before making another attempt
                Thread.Sleep(attemptWaitMS);

            }

        }

    }
    // Reutn the filestream, may be valid or null
    return fs;
}