A Plug-in Wizard Framework

using System;
using System.Collections.Generic;
using System.Windows.Forms;

namespace Clifton.Wizard.Interfaces
{
	/// <summary>
	/// This abstract class defines common fields, properties, and certain
	/// default behavior that each plugin can leverage.
	/// </summary>
	public abstract class WizardBase : IPlugin
	{
		/// <summary>
		/// The event that the plugin can use to notify the wizard of a state change.
		/// </summary>
		public event EventHandler UpdateStateEvent;
		
		/// <summary>
		/// The control list is preserved so that the control's state is maintained
		/// as the user navigates backwards and forwards through the wizard.
		/// </summary>
		protected List<Control> ctrlList;
		protected Form form;

		/// <summary>
		/// True if the plugin's data is validated and the user can proceed with
		/// the next wizard page.  True is the default.
		/// </summary>
		public virtual bool IsValid
		{
			get { return true; }
		}

		/// <summary>
		/// True if the plugin is going to provide help.  The default is false.
		/// </summary>
		public virtual bool HasHelp
		{
			get { return false; }
		}

		/// <summary>
		/// Constructor.
		/// </summary>
		public WizardBase()
		{
			ctrlList = new List<Control>();
		}

		/// <summary>
		/// The plugin can override this method if it needs to do
		/// something before the wizard proceeds to the next page.
		/// </summary>
		public virtual void OnNext()
		{
			// Do nothing.
		}

		/// <summary>
		/// The plugin can override this method if it wants to display 
		/// some help.
		/// </summary>
		public virtual void OnHelp()
		{
			// Do nothing.
		}

		/// <summary>
		/// Returns the controls from the form that the plugin assigned
		/// in the class.  The plugin can override this method to return
		/// a custom control list.
		/// </summary>
		/// <returns></returns>
		public virtual List<Control> GetControls()
		{
			// If this is the first time we're calling this method,
			// load the controls from the plugin form.
			if (ctrlList.Count == 0)
			{
				// Once loaded, we reuse the same control instances
				// which as the advantage of preserving state if the
				// user goes back to a previous page (and forward again.)
				GetFormControls();
			}

			// Otherwise, return the control list that we acquired from
			// the form. 
			return ctrlList;
		}

		/// <summary>
		/// Iterates through the form's top level controls to construct
		/// a list of form controls.
		/// </summary>
		protected virtual void GetFormControls()
		{
			foreach (Control c in form.Controls)
			{
				ctrlList.Add(c);
			}
		}

		/// <summary>
		/// The plugin can call this method to raise the UpdateStateEvent,
		/// which informs the wizard that the button states need to be updated.
		/// </summary>
		protected void RaiseUpdateState()
		{
			if (UpdateStateEvent != null)
			{
				UpdateStateEvent(this, EventArgs.Empty);
			}
		}
	}
}