Is there a way of using one method to handle others to avoid code duplication?

Question

I wonder if there is a way of writing a method or a class that would add to any method some code that is shared between many methods. The methods return different things and some of them are just void.

Below is a part of the code that is duplicated in the methods.

StartTimer(MethodBase.GetCurrentMethod().Name);
try
{
    // Actual method body
}
catch (Exception ex)
{
    bool rethrow = ExceptionPolicy.HandleException(ex, "DALPolicy");
    if (rethrow)
    {
         throw;
    }
}
finally
{
    StopTimer(MethodBase.GetCurrentMethod().Name);
}

Any help would be greatly appreciated.

---

Nix solution applied to the code above

public T WrapMethod<T>(Func<T> func)
{
    StartTimer(func.Method.Name);
    try
    {
        return func();
    }
    catch (Exception ex)
    {
        bool rethrow = ExceptionPolicy.HandleException(ex, "DALPolicy");
        if (rethrow)
        {
            throw;
        }
    }
    finally
    {
        StopTimer(func.Method.Name);
    }
    return default(T);
}

Answer 1

I actually had this same issue....

C# searching for new Tool for the tool box, how to template this code

public Result<Boolean> CreateLocation(LocationKey key)
{
    LocationDAO locationDAO = new LocationDAO();
    return WrapMethod(() => locationDAO.CreateLocation(key));
}


public Result<Boolean> RemoveLocation(LocationKey key)
{
    LocationDAO locationDAO = new LocationDAO();
    return WrapMethod(() =>  locationDAO.RemoveLocation(key));
}


static Result<T> WrapMethod<T>(Func<Result<T>> func)
{
    try
    {
        return func();
    }
    catch (UpdateException ue)
    {
        return new Result<T>(default(T), ue.Errors);
    }
}

Answer 2

That's usually accomplished with Aspect Oriented Programming and as far as I know there is no support, currently, in the .NET framework (or C#) for this feature. See this post.

Also, as far as I could grasp - without having done any testing myself - it seems that frameworks that provide AOP features to .NET based on the ContextBoundObject class incur a lot of performance overhead so you may wish to consider that when making the decision whether the advantage of ease-of-use is greater than the disadvantage in performance.

Answer 3

You can use delegates and generic delegates such as public delegate T Func<T>(); to pass in the code to be wrapped. In the below example I needed something similar where I wanted my retry logic to be reused in many scenarios. In the example at the beginning you see how this is used to pass in my anonymous delegates:

public class RetryOnError
{
    static void Example()
    {
      string endOfLineChar = Environment.NewLine;
      RetryOnError.RetryUntil<string>(delegate()
      {
          //attempt some potentially error throwing operations here

          //you can access local variables declared outside the the Retry block:
          return "some data after successful processing" + endOfLineChar;
      },
      new RetryOnError.OnException(delegate(ref Exception ex, ref bool rethrow)
      {
          //respond to the error and
          //do some analysis to determine if a retry should occur
          //perhaps prompting the user to correct a problem with a retry dialog
          bool shouldRetry = false;

          //maybe log error
          log4net.Error(ex);

          //maybe you want to wrap the Exception for some reason
          ex = new Exception("An unrecoverable failure occurred.", ex);
          rethrow = true;//maybe reset stack trace

          return shouldRetry;//stop retrying, normally done conditionally instead
      }));
    }

  /// <summary>
  /// A delegate that returns type T
  /// </summary>
  /// <typeparam name="T">The type to be returned.</typeparam>
  /// <returns></returns>
  public delegate T Func<T>();

  /// <summary>
  /// An exception handler that returns false if Exception should be propogated
  /// or true if it should be ignored.
  /// </summary>
  /// <returns>A indicater of whether an exception should be ignored(true) or propogated(false).</returns>
  public delegate bool OnException(ref Exception ex, ref bool rethrow);

  /// <summary>
  /// Repeatedly executes retryThis until it executes successfully with
  /// an exception, maxTries is reached, or onException returns false.
  /// If retryThis is succesful, then its return value is returned by RetryUntil.
  /// </summary>
  /// <typeparam name="T">The type returned by retryThis, and subsequently returned by RetryUntil</typeparam>
  /// <param name="retryThis">The delegate to be called until success or until break condition.</param>
  /// <param name="onException">Exception handler that can be implemented to perform logging,
  /// notify user, and indicates whether retrying should continue.  Return of true indicates
  /// ignore exception and continue execution, and false indicates break retrying and the
  /// exception will be propogated.</param>
  /// <param name="maxTries">Once retryThis has been called unsuccessfully <c>maxTries</c> times, then the exception is propagated.
  /// If maxTries is zero, then it will retry forever until success.
  /// </param>
  /// <returns>The value returned by retryThis on successful execution.</returns>
  public static T RetryUntil<T>(Func<T> retryThis, OnException onException, int maxTries)
  {
    //loop will run until either no exception occurs, or an exception is propogated(see catch block)
    int i = 0;
    while(true)
    {
      try
      {
        return retryThis();
      }
      catch ( Exception ex )
      {
        bool rethrow =false;//by default don't rethrow, just throw; to preserve stack trace
        if ( (i + 1) == maxTries )
        {//if on last try, propogate exception
          throw;
        }
        else if (onException(ref ex, ref rethrow))
        {
          if (maxTries != 0)
          {//if not infinite retries
            ++i;
          }
          continue;//ignore exception and continue
        }
        else
        {
          if (rethrow)
          {
            throw ex;//propogate exception
          }
          else
          {//else preserve stack trace
            throw;
          }
        }
      }
    }
  }

  /// <summary>
  /// Repeatedly executes retryThis until it executes successfully with
  /// an exception, or onException returns false.
  /// If retryThis is succesful, then its return value is returned by RetryUntil.
  /// This function will run infinitly until success or onException returns false.
  /// </summary>
  /// <typeparam name="T">The type returned by retryThis, and subsequently returned by RetryUntil</typeparam>
  /// <param name="retryThis">The delegate to be called until success or until break condition.</param>
  /// <param name="onException">Exception handler that can be implemented to perform logging,
  /// notify user, and indicates whether retrying should continue.  Return of true indicates
  /// ignore exception and continue execution, and false indicates break retrying and the
  /// exception will be propogated.</param>
  /// <returns></returns>
  public static T RetryUntil<T>(Func<T> retryThis, OnException onException)
  {
    return RetryUntil<T>(retryThis, onException, 0);
  }
}