C# - User Settings broken

Question

We had a rare exception occur when reading the standard .Net user settings (this are the ones found in \"project properties\" in VS 2008):

System.Configurati         


        

Answer 1

The way to programmatically recover is to do what you did manually - delete the user settings file. Then call Settings.Reset. (You could also write a new user settings file with default values instead of deleting it, but if you're using the configuration manager properly that's essentially the same thing.)

This is a pretty rare occurrence, but it's not totally unheard of. Not only can your program crash while writing the user settings file, the file itself is user-writeable, so other programs the user runs could mess with it.

To avoid this particular vulnerability, persist user settings in a durable store with transactional integrity, i.e. a database. (You'll still have vulnerabilities, just not this one.) That's a lot of work for what in most cases will be a marginal improvement in reliability. But "in most cases" doesn't mean "in all cases;" yours may warrant it.

Answer 2

Here's a solution that does not require you to exit the application with kudos to Jarle (http://www.codeproject.com/Articles/30216/Handling-Corrupt-user-config-Settings?msg=3608682#xx3608682xx). Early on, before Settings ever gets called, use this

    public static bool CheckSettings()
    {
        var isReset = false;

        try
        {
            ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.PerUserRoamingAndLocal);
        }
        catch (ConfigurationErrorsException ex)
        {
            string filename = string.Empty;
            if (!string.IsNullOrEmpty(ex.Filename))
            {
                filename = ex.Filename;
            }
            else
            {
                var innerEx = ex.InnerException as ConfigurationErrorsException;
                if (innerEx != null && !string.IsNullOrEmpty(innerEx.Filename))
                {
                    filename = innerEx.Filename;
                }                   
            }

            if (!string.IsNullOrEmpty(filename))
            {
                if (System.IO.File.Exists(filename))
                {
                    var fileInfo = new System.IO.FileInfo(filename);
                    var watcher
                         = new System.IO.FileSystemWatcher(fileInfo.Directory.FullName, fileInfo.Name);
                    System.IO.File.Delete(filename);
                    isReset = true;
                    if (System.IO.File.Exists(filename))
                    {
                        watcher.WaitForChanged(System.IO.WatcherChangeTypes.Deleted);
                    }
                }
            }
        }

        return isReset;
    }

Essentially, rather than relying on Sittings to throw the error, read the file with the ConfigurationManager, that way the system's version never gets into a bad state.

Answer 3

[STAThread]
private static void Main(string[] args)
{
    try
    {
        // ...
    }
    catch (System.Configuration.ConfigurationErrorsException ex)
    {   
        var config = ((System.Configuration.ConfigurationErrorsException)ex.InnerException).Filename;
        // notify user, ask them to restart
        System.IO.File.Delete(config);
        Application.Exit();
    }
}