exceptions.md

Your original example:

public virtual List<UserDC> GetAllActiveAgentsByReason(int reasonID)
{
    try
    {
        if (reasonID < 0)
        {
            throw new ArgumentException("An invalid reasonID was passed.");
        }

        return accessManagerDAO.GetAllActiveAgentsByReason(reasonID);
    }
    catch (Exception ex)
    {
        if (ex is AMSException)
        {
            throw;
        }
        else
        {
            throw new AMSException(ex.Message, ex.InnerException);
        }
    }
}

The catch clause can't really be moved out of this method because of the bare throw, but you could get tricky with delegates:

public virtual List<UserDC> GetAllActiveAgentsByReason(int reasonID)
{
    return TryHelper(() =>
    {
        if (reasonID < 0)
        {
            throw new ArgumentException("An invalid reasonID was passed.");
        }

        return accessManagerDAO.GetAllActiveAgentsByReason(reasonID);
    });
}

Now the amount of "business" code in that method isn't dwarfed by the error handling code.

The TryHelper method can be defined like this:

protected T TryHelper<T>(Func<T> action)
{
    try
    {
        return action();
    }
    catch (Exception ex)
    {
        if (ex is AMSException)
        {
            throw;
        }
        else
        {
            throw new AMSException(ex.Message, ex.InnerException);
        }
    }
}

I marked it protected so that it could go in the base class, but if you don't have a common base class, you can put it wherever and mark it public so it's accessible and static so that it's easy to invoke.

jdiamond/exceptions.md