{ ID = 3, CustomerName = xyz, SaleDate = 05.08.2013 00:00:00, TotalAmount = 10 }

var copyitem = Datagrid_NewSale.SelectedItem;

if (copyitem == null)
{
    MessageBox.Show("Please select values from list");
}
if (copyitem != null)
{
    MessageBox.Show(copyitem.ToString());
}

public class CustomerDetailes
{
    public string CustomerName { get; set; }
}

public void viewcustomername()
{
    List<CustomerDetailes> ilist = null;
    ilist = (from order in db.Customer
                select new CustomerDetailes
                {
                    CustomerName= order.CustomerName
                }).ToList();
    txtCustumer.Text = ilist.ToString();

}

CustomerDetailes copyitem = (CustomerDetailes)Datagrid_NewSale.SelectedItem;

if (copyitem == null)
{
    MessageBox.Show("Please select values from list");
}
if (copyitem != null)
{
    MessageBox.Show(copyitem.ToString());
}

txtCustomer.text=copyitem.CustomerName;  //CustomerName into a textbox

List<CustomerDetails> customerDetails = new List<CustomerDetails>();
    List<CustomerDetails> MyCollection
    {
        get
        {

            return myList;
        }
        set
        {
            myList = value;
            PropertyChanged(this, new PropertyChangedEventArgs("MyCollection"));
        }
    }

<DataGrid ItemsSource="{Binding MyCollection}"/>

dataGrid.Items.Add(new CustomerDetails(){Name = "abc"}, xyz propertis)

dynamic copyitem = dataGrid1.SelectedItem;

int localId = copyitem.ID;

var query= (from order in db.Customer
where order.ID=localId
select order).ToList();