WPF Charting using MVVM Pattern

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Collections.ObjectModel;
using System.Windows.Controls.DataVisualization.Charting;
using System.Windows.Controls;

namespace WPFCharting 
{
    public class MainWindowVM: INotifyPropertyChanged
    {
        private MainWindowModel _mwm;
        private static MainWindowVM _VM;
        /// <summary>
        /// Gets the singleton instance of this Viewmodel.
        /// </summary>
        /// <returns>This instance of MainWindowVM or Null if not instanciated</returns>
        public static MainWindowVM getInstance()
        {
            return _VM;
        }
        /// <summary>
        /// CTOR for MainWindowVM - View Model for MainWindow
        /// </summary>
        public MainWindowVM ()
        {
            //store this instance;
            _VM = this;
            //create a new moel
            _mwm = new MainWindowModel();
            //the model IS the data, this is a getter only method
            _data = _mwm;
            propChanged("data");
            //set default chart type
            CurrentChartType = "ColumnSeries";
            //default title
            Title = "Welcome to WPFCharting";
            //Default Legend Title
            LegendTitle = "Animals";    
            //Allow user to dynamically change chart types
            SeriesTypes =  new ObservableCollection<string>();
           // MainChart = new ucColumnSeriesChart();
            
        }
        private ObservableCollection<KeyValuePair<string, int>> _data;
        public ObservableCollection<KeyValuePair<string,int>> data {
            get { return _data; }          
        }
        private ContentControl _MainChart;
        public ContentControl MainChart {
            get { return _MainChart; }
            set { 
                _MainChart = value;
                propChanged("MainChart");            
            } 
        }
        private string _CurrentChartType;
        public string CurrentChartType {
            get { return _CurrentChartType; }
            set { 
                _CurrentChartType = value;
                Commands.ShowSeries ss = new Commands.ShowSeries();
                ss.Execute(value);
                propChanged("CurrentChartType");
            }
        }     
        private ObservableCollection<string> _SeriesTypes;
        public ObservableCollection<string> SeriesTypes {
            get { return _SeriesTypes; }
            set {
                Utilities.ForChart fc = new Utilities.ForChart();
                _SeriesTypes = fc.getChartSeriesTypes();
                propChanged("SeriesTypes");              
            }  
        }
        private string _LegendTitle;
        public string LegendTitle { 
            get {return _LegendTitle;} 
            set {
                _LegendTitle = value;
                propChanged("LegendTitle");
            }
        }
        private string _Title;
        /// <summary>
        /// The title to the chart
        /// </summary>
        public string Title { 
            get {return _Title;}
            set { 
                _Title = value;
                propChanged("Title");
            } 
        }
        public event PropertyChangedEventHandler PropertyChanged;
        public void propChanged(String propname)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propname));
            }
        }
    }
}