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Propagator in C# - An Alternative to the Observer Design Pattern

, 13 Jul 2009
Re-usable implementation of the Propagator Design Pattern in C#, a potentially more powerful alternative to the well-known Observer Design Pattern.
// Martijn Boeker, July 14, 2009
// License: The Code Project Open License (CPOL) 1.02

using System;
using System.Collections.Generic;
using System.Text;

namespace MB.Propagators
{
    /// <summary>
    /// Encapsulates state change to be propagated. The StateChangeTypeID is used by the
    /// Propagator class to dispatch state change handler methods.
    /// </summary>
    public class StateChange
    {
        #region Data Members

        private readonly int _stateChangeTypeID;
        private List<IPropagator> _observedBy = new List<IPropagator>();

        #endregion

        #region Constructors

        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="stateChangeTypeID">Identifies type of state change.</param>
        public StateChange(int stateChangeTypeID)
        {
            _stateChangeTypeID = stateChangeTypeID;
        }

        #endregion

        #region Properties

        /// <summary>
        /// ID of the type of command.
        /// </summary>
        public int StateChangeTypeID
        {
            get
            {
                return _stateChangeTypeID;
            }
        }

        #endregion

        #region Methods

        /// <summary>
        /// Indicate that the given propagator has observed this command.
        /// </summary>
        /// <param name="propagator"></param>
        public void AddObservedBy(IPropagator propagator)
        {
            _observedBy.Add(propagator);
        }

        /// <summary>
        /// Find out if the given propagator has observed this command.
        /// </summary>
        /// <param name="propagator"></param>
        /// <returns></returns>
        public bool HasBeenObservedBy(IPropagator propagator)
        {
            return _observedBy.Contains(propagator);
        }

        #endregion
    }
}

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License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Martijn Boeker
Software Developer (Senior) Phi International
Canada Canada
Grew up in Amsterdam, now living in downtown Vancouver. There are definitely more mountains here.
 
My first internship was with the first company in the Netherlands to teach C++ (www.datasim.nl). During this internship I got to know Object Oriented Design, which kept my interest until this day. In the mean time, I have worked for different companies in the Netherlands and Canada. I have done most of my recent work in C#, developing Database/Web/Desktop applications.
 
I am currently working as a freelance Software Developer for PHI International in Amsterdam.
 
The CodeProject rocks!

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