Building a puzzle game using Generics

#region == Application Information ==
//
// Author: Carlos R Lacerda
// email: carlos@byteshift.com
// website: www.byteshift.com
// Date: 08/15/2004
// version: 1.0.0.0
// All rights reserved
//
#endregion

#region Using directives

using System;
using System.Windows.Forms;
using System.Windows.Forms.Design;
using System.Collections.Generic;
using System.Text;
using System.Drawing;

#endregion

namespace WinGenericsDemo
{
    /// <summary>
    /// This is the game item class
    /// </summary>
    public partial class GameItems
    {
        #region Add Methods
        /// <summary>
        /// Add the selected piece to the target head list
        /// </summary>
        /// <returns>Returns null or the control added</returns>
        public PictureBox AddPieceToHead()
        {
            Item selectedItem = null;
            // verify if there is a selected item in source list
            selectedItem = GetSelectedItem(sourceListItems);
            // if null, need select an item
            if (selectedItem != null)
            {
                // add item to target
                targetListItems.AddHead(selectedItem);
                // remove from source list
                sourceListItems.Remove(selectedItem);

                // try to shift all items to accomodete the new added
                Point nextPosition = solutionPosition;
                // update the list
                UpdatePositionForEntireList(targetListItems, nextPosition);
            }
            else
                return null;
            return selectedItem.PicItem;
        }

        /// <summary>
        /// Add the selected piece to the target tail list
        /// </summary>
        /// <returns>Returns null or the control added</returns>
        public PictureBox AddPieceToTail()
        {
            Item selectedItem = null;
            // verify if there is a selected item in source list
            selectedItem = GetSelectedItem(sourceListItems);
            // if null, need select an item
            if (selectedItem != null)
            {
                // add item to tail
                targetListItems.AddTail(selectedItem);
                // remove from source list
                sourceListItems.Remove(selectedItem);
                // unselect the item
                selectedItem.IsSelected = false;
                // because the new item goes to the end list , there is
                // no need to shift the others
                if (targetListItems.Count == 1)
                    selectedItem.UpdatePosition(solutionPosition);
                else
                {
                    // there is more than one item. Need to find the sibiling
                    Item sibiling = targetListItems.GetSiblingItem(selectedItem, false);
                    selectedItem.UpdatePosition(UpdateNextPosition(sibiling));
                }
            }
            else
                return null;
            return selectedItem.PicItem;
        }

        /// <summary>
        /// Add the selected source piece before the selected target
        /// </summary>
        /// <returns>Returns null or the control added</returns>
        public PictureBox AddPieceBefore()
        {
            Item selectedSrcItem = null;
            Item selectedTgtItem = null;

            // get the selected item in source list
            selectedSrcItem = GetSelectedItem(sourceListItems);
            // get the selected item in target list
            selectedTgtItem = GetSelectedItem(targetListItems);

            // if null, need select an item
            if (selectedSrcItem != null && selectedTgtItem != null)
            {
                // add item to tail
                targetListItems.AddBeforeItem(selectedTgtItem, selectedSrcItem);
                // remove from source list
                sourceListItems.Remove(selectedSrcItem);
                // unselect the item
                selectedSrcItem.IsSelected = false;
                selectedTgtItem.IsSelected = false;

                // try to shift all items to accomodete the new added
                Point nextPosition = solutionPosition;
                // update the list
                UpdatePositionForEntireList(targetListItems, nextPosition);
            }
            else
                return null;
            return selectedSrcItem.PicItem;
        }

        /// <summary>
        /// Add the selected source piece after the selected target
        /// </summary>
        /// <returns>Returns null or the control added</returns>
        public PictureBox AddPieceAfter()
        {
            Item selectedSrcItem = null;
            Item selectedTgtItem = null;

            // get the selected item in source list
            selectedSrcItem = GetSelectedItem(sourceListItems);
            // get the selected item in target list
            selectedTgtItem = GetSelectedItem(targetListItems);

            // if null, need select an item
            if (selectedSrcItem != null && selectedTgtItem != null)
            {
                // add item to tail
                targetListItems.AddAfterItem(selectedTgtItem, selectedSrcItem);
                // remove from source list
                sourceListItems.Remove(selectedSrcItem);
                // unselect the item
                selectedSrcItem.IsSelected = false;
                selectedTgtItem.IsSelected = false;

                // try to shift all items to accomodete the new added
                Point nextPosition = solutionPosition;
                // update the list
                UpdatePositionForEntireList(targetListItems, nextPosition);
            }
            else
                return null;
            return selectedSrcItem.PicItem;
        }
        #endregion

    }
}