Silverlight Application with MVVM WCF and EF

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.ComponentModel;
using System.Collections.ObjectModel;
using SilverlightMVVMwithWCFandLinq.MyServiceReference;

namespace SilverlightMVVMwithWCFandLinq
{
    public class MainViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        private ObservableCollection<SchoolClass> _SchoolClasses;
        private ObservableCollection<string> _Classes;
        public ObservableCollection<SchoolClass> SchoolClasses
        {
            get
            {
                return _SchoolClasses;
            }
            set
            {
                _SchoolClasses = value;
                NotifyPropertyChanged("SchoolClasses");
            }
        }


        public ObservableCollection<string> Classes
        {
            get
            {
                return _Classes;
            }
            set
            {
                _Classes = value;
                NotifyPropertyChanged("Classes");
            }

        }

        public MainViewModel()
        {
            MyServiceReference.Service1Client client = new MyServiceReference.Service1Client();

            client.GetClassesCompleted += new EventHandler<MyServiceReference.GetClassesCompletedEventArgs>(client_GetClassesCompleted);
            client.GetClassesAsync();
            client.GetSchoolClassesCompleted += new EventHandler<GetSchoolClassesCompletedEventArgs>(client_GetSchoolClassesCompleted);
            client.GetSchoolClassesAsync();
        }

        void client_GetSchoolClassesCompleted(object sender, GetSchoolClassesCompletedEventArgs e)
        {
            SchoolClasses = e.Result;
        }

        void client_GetClassesCompleted(object sender, MyServiceReference.GetClassesCompletedEventArgs e)
        {
            Classes = e.Result;
        }


        protected void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }


    }
}