ObservableCollection<ViewModelBase> _viewModel; ///whats this 

        #endregion Fields

        #region Constructors

        public MainWindowViewModel()
        {
            _employeeRespository = new EmployeeRespository();
            //create an instance of out viewmodel add it to our collection ;
            EmployeeListViewModel vmEmployee = new EmployeeListViewModel(_employeeRespository);
            this.ViewModels.Add(vmEmployee);
        }
        /// <summary>
        /// Construct
        /// </summary>
        /// <param name="_employeeList"></param>
        public EmployeeListViewModel(EmployeeRespository employeeRespository)
        {
            if (employeeRespository == null)
            { throw new ArgumentNullException("employeeRespository"); }

            _employeeRespository = employeeRespository;
            this.AllEmployees = new ObservableCollection<Model.Employee>(_employeeRespository.GetEmployee());
        }