Propagator in C# - An Alternative to the 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.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using MB.Propagators;

namespace PropagatorDemo
{
    /// <summary>
    /// This form contains a user control for selecting a font (FontControl) 
    /// and a user control for selecting a color (ColorControl). Both controls 
    /// display an example text with the current font and color. The demo form
    /// itself also has example text that displays the current font
    /// and color selection.
    /// 
    /// There is a bi-directional propagator link from the DemoForm
    /// to the FontControl and from the DemoForm to the ColorControl.
    /// Any state change is communicated to all propagators in the network.
    /// This demo demonstrates the following routes:
    /// 
    ///  - Initialize/reset: from DemoForm to FontControl and ColorControl
    ///  - Change font: from FontControl to DemoForm and ColorControl
    ///  - Change color: from ColorControl to DemoForm and FontControl.
    /// 
    /// </summary>
    public partial class DemoForm : Form
    {
        private Propagator _propagator = new Propagator("DemoForm");

        /// <summary>
        /// Constructor.
        /// </summary>
        public DemoForm()
        {
            InitializeComponent();

            // Add font and color controls as dependents.
            _propagator.AddDependent(fontControl.Propagator, true);
            _propagator.AddDependent(colorControl.Propagator, true);

            // Add font and color change handlers.
            _propagator.AddHandler(FontChange.ID, HandleFontChange);
            _propagator.AddHandler(ColorChange.ID, HandleColorChange);

            // Initialize font and color.
            Initialize();
        }
                
        /// <summary>
        /// Reset font and color.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void buttonReset_Click(object sender, EventArgs e)
        {
            Initialize();
        }

        /// <summary>
        /// Initialize font and color.
        /// </summary>
        private void Initialize()
        {
            ColorChange colorChange = new ColorChange(Color.Blue);
            _propagator.Process(colorChange);

            Font font = new Font("Arial", 14);
            FontChange fontChange = new FontChange(font);
            _propagator.Process(fontChange);
        }

        /// <summary>
        /// Handle color change event.
        /// </summary>
        /// <param name="stateChange"></param>
        public void HandleColorChange(StateChange stateChange)
        {
            ColorChange colorChange = stateChange as ColorChange;
            if (colorChange != null)
            {
                // Set color of example text.
                labelExample.ForeColor = colorChange.Color;
            }
        }

        /// <summary>
        /// Handle font change event.
        /// </summary>
        /// <param name="stateChange"></param>
        public void HandleFontChange(StateChange stateChange)
        {
            FontChange fontChange = stateChange as FontChange;
            if (fontChange != null)
            {
                // Set font of example text.
                labelExample.Font = fontChange.Font;
            }
        }
    }
}