Equation Calculator with Graphing

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections.ObjectModel;
using System.Xml;
using CommonUtils;
using System.ComponentModel;
using System.Windows.Media;
using System.Windows;
using System.Windows.Controls;

namespace Calculator
{
	public class GraphItem : CommonUtils.IXmlSerialize, INotifyPropertyChanged
	{
		bool m_isEnabled = false;
		string m_equation = string.Empty;
		Brush m_color;
		public bool IsSelected {get; set;}
		public bool IsEnabled
		{
			get { return m_isEnabled; }
			set
			{
				if (m_isEnabled != value)
				{
					m_isEnabled = value;
					NotifyChange("IsEnabled");
				}
			}
		}
		public string Equation
		{
			get { return m_equation;}
			set
			{
				m_equation = value;
				NotifyChange("Equation");
			}
		}
		public string Vars {get; set;}
		public Brush GraphColor 
		{
			get { return m_color; }
			set
			{
				m_color = value;
				NotifyChange("GraphColor");
			}
		}

		public GraphItem()
		{
			GraphColor = Brushes.Beige;
		}
		public GraphItem(XmlElement node)
		{
			Read(node);
		}
		public void Read(XmlElement node)
		{
			try
			{
				if (node != null && node.Name == "graphitem")
				{
					IsEnabled = node.GetBool("enable", true);
					Equation = node.GetString("eq", string.Empty);
					Vars = node.GetString("vars", string.Empty);
					GraphColor = node.GetBrush("color", Brushes.Blue);
				}
			}
			catch { }
		}
		public void Write(XmlTextWriter wr)
		{
			wr.WriteStartElement("graphitem");
			wr.WriteAttribute("enable", IsEnabled);
			wr.WriteAttribute("eq", Equation);
			wr.WriteAttribute("vars", Vars);
			wr.WriteAttribute("color", GraphColor);
			wr.WriteEndElement();
		}

		#region INotifyPropertyChanged Members
		void NotifyChange(string property)
		{
			if (PropertyChanged != null)
				PropertyChanged(this, new PropertyChangedEventArgs(property));
		}
		public event PropertyChangedEventHandler PropertyChanged;

		#endregion
	}

	public class NewGraphItem : GraphItem
	{
	}

	public class GraphItemCollection : ObservableCollection<GraphItem>, CommonUtils.IXmlSerialize
	{
		public const string xmlTag = "graphitems";
		public new void Add(GraphItem item)
		{
			RemoveNewItem();
			base.Add(item);
			AddNewItem();
		}
		public void Read(XmlElement node)
		{
			try
			{
				if (node != null && node.Name == xmlTag)
				{
					Clear();
					foreach (XmlNode child in node.ChildNodes)
					{
						XmlElement element = child as XmlElement;
						if (element == null)
							continue;
						base.Add(new GraphItem(element));
					}
					AddNewItem();
				}
			}
			catch { }
		}
		public void Write(XmlTextWriter wr)
		{
			wr.WriteStartElement("graphitems");
			foreach(IXmlSerialize item in this)
			{
				if (item is NewGraphItem)
					continue;
				item.Write(wr);
			}
			wr.WriteEndElement();
		}
		void RemoveNewItem()
		{
			for (int index = Count - 1; index >= 0; index--)
			{
				if (this[index] is NewGraphItem)
					RemoveAt(index);
			}
		}
		void AddNewItem()
		{
			base.Add(new NewGraphItem());
		}
	}
}