Layers Pattern in Practice

using BillsEntityLib;
using System.Collections.ObjectModel;
using Microsoft.Windows.Controls;

namespace BillPayManager
{
    public interface IDataGridProxy
    {
        void Initialize(DataGrid dataGrid, Bills bills);

        void UpdateDataGrid(Bills bills);

        void CommitChangesToDataSource();

        void InsertBillToDataGrid(Bill bill);

        event System.Collections.Specialized.NotifyCollectionChangedEventHandler CollectionChanged;

        event System.ComponentModel.PropertyChangedEventHandler BillPropertyChanged;

        Microsoft.Windows.Controls.DataGrid DataGrid
        {
            get;
        }
        ObservableCollection<Bill> Collection
        {
            get;
        }
    }
}