Reducing duplicate error handling code in C#?

Just wondering, what do you feel your method leaves to be desired? You could replace the anonymous delegate with a.. named? delegate, something like

    public delegate void IoOperation(params string[] parameters);

    public void FileDeleteOperation(params string[] fileName)
    {
        File.Delete(fileName[0]);
    }

    public void FileCopyOperation(params string[] fileNames)
    {
        File.Copy(fileNames[0], fileNames[1]);
    }

    public void RetryFileIO(IoOperation operation, params string[] parameters)
    {
        RetryTimer fileIORetryTimer = new RetryTimer(TimeSpan.FromHours(10));
        bool success = false;
        while (!success)
        {
            try
            {
                operation(parameters);
                success = true;
            }
            catch (IOException e)
            {
                if (fileIORetryTimer.HasExceededRetryTimeout)
                {
                    throw;
                }
                fileIORetryTimer.SleepUntilNextRetry();
            }
        }
    }

    public void Foo()
    {
        this.RetryFileIO(FileDeleteOperation, "L:\file.to.delete" );
        this.RetryFileIO(FileCopyOperation, "L:\file.to.copy.source", "L:\file.to.copy.destination" );
    }

You could also use a more OO approach:

• Create a base class that does the error handling and calls an abstract method to perform the concrete work. (Template Method pattern)
• Create concrete classes for each operation.

This has the advantage of naming each type of operation you perform and gives you a Command pattern - operations have been represented as objects.

This looks like an excellent opportunity to have a look at Aspect Oriented Programming. Here is a good article on AOP in .NET. The general idea is that you'd extract the cross-functional concern (i.e. Retry for x hours) into a separate class and then you'd annotate any methods that need to modify their behaviour in that way. Here's how it might look (with a nice extension method on Int32)

[RetryFor( 10.Hours() )]
public void DeleteArchive()
{
  //.. code to just delete the archive
}

Here's what I did recently. It has probably been done elsewhere better, but it seems pretty clean and reusable.

I have a utility method that looks like this:

    public delegate void WorkMethod();

    static public void DoAndRetry(WorkMethod wm, int maxRetries)
    {
        int curRetries = 0;
        do
        {
            try
            {
                wm.Invoke();
                return;
            }
            catch (Exception e)
            {
                curRetries++;
                if (curRetries > maxRetries)
                {
                    throw new Exception("Maximum retries reached", e);
                }
            }
        } while (true);
    }

Then in my application, I use c#'s Lamda expression syntax to keep things tidy:

Utility.DoAndRetry( () => ie.GoTo(url), 5);

This calls my method and retries up to 5 times. At the fifth attempt, the original exception is rethrown inside of a retry exception.