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.Drawing;
using System.Data;
using System.Text;
using System.Windows.Forms;
using MB.Propagators;

namespace PropagatorDemo
{
    /// <summary>
    /// Control for choosing color.
    /// </summary>
    public partial class ColorControl : UserControl
    {
        private Color _currentColor = Color.Black;
        private Propagator _propagator = new Propagator("ColorControl");

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

            _propagator.AddHandler(ColorChange.ID, HandleColorChange);
            _propagator.AddHandler(FontChange.ID, HandleFontChange);
        }

        /// <summary>
        /// Access to propagator.
        /// </summary>
        public IPropagator Propagator
        {
            get
            {
                return _propagator;
            }
        }

        /// <summary>
        /// Select new color.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void buttonSelectColor_Click(object sender, EventArgs e)
        {
            ColorDialog colorDialog = new ColorDialog();
            colorDialog.Color = _currentColor;

            DialogResult result = colorDialog.ShowDialog();
            if (result == DialogResult.OK)
            {
                ColorChange colorChange = new ColorChange(colorDialog.Color);
                _propagator.Process(colorChange);
            }
        }

        /// <summary>
        /// Handle color change event.
        /// </summary>
        /// <param name="stateChange"></param>
        private void HandleColorChange(StateChange stateChange)
        {
            ColorChange colorChange = stateChange as ColorChange;
            if (colorChange != null)
            {
                Color newColor = colorChange.Color;

                // Set color of example text.
                labelExample.ForeColor = newColor;

                // Set background of color panel.
                panelColor.BackColor = newColor;

                // Remember the current color.
                _currentColor = newColor;
            }
        }

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