Implement Selectable Virtual List

using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;

namespace SelectableVirtualList
{
	public class ViewModel : INotifyPropertyChanged
	{
		public ObservableCollection<Employee> SelectedEmployeeCollection
		{
			get; 
			set;
		}

		private SelectableVirtualList<Employee> _AvailableEmployeeCollection;
		public SelectableVirtualList<Employee> AvailableEmployeeCollection
		{
			get { return _AvailableEmployeeCollection; }
			set
			{
				_AvailableEmployeeCollection = value;
				OnPropertyChanged("AvailableEmployeeCollection");
			}
		}

		public ViewModel()
		{
			AvailableEmployeeCollection = new SelectableVirtualList<Employee>(new EmployeeObjectGenerator());
			SelectedEmployeeCollection = new ObservableCollection<Employee>();
		}

		public void Add()
		{
			IList<Employee> employees = AvailableEmployeeCollection.SelectedList;
			foreach (var employee in employees)
			{
				employee.IsSelected = false;
				if (!SelectedEmployeeCollection.Contains(employee))
				{
					SelectedEmployeeCollection.Add(employee);
				}
				AvailableEmployeeCollection.Remove(employee);
			}
		}

		public void Remove()
		{
			int internalStandardCount = SelectedEmployeeCollection.Count;
			for (int i = internalStandardCount - 1; i >= 0; i--)
			{
				Employee answerInstance = SelectedEmployeeCollection[i];
				if (answerInstance.IsSelected)
				{
					answerInstance.IsSelected = false;
					if (!AvailableEmployeeCollection.Contains(answerInstance))
					{
						AvailableEmployeeCollection.Add(answerInstance);
					}
					SelectedEmployeeCollection.Remove(answerInstance);
				}
			}
		}

		public void SelectAvailableList()
		{
			AvailableEmployeeCollection.SelectAll();
			OnPropertyChanged("AvailableEmployeeCollection");
		}

		public void DeselectAvailableList()
		{
			AvailableEmployeeCollection.DeSelectAll();
			OnPropertyChanged("AvailableEmployeeCollection");
		}

		public event PropertyChangedEventHandler PropertyChanged;
		public void OnPropertyChanged(string name)
		{
			PropertyChangedEventHandler handler = PropertyChanged;
			if (handler != null)
			{
				handler(this, new PropertyChangedEventArgs(name));
			}
		}
	}
}