private async void LoadProductsAndCustomers()
        {
            ZzaProxy proxy = new ZzaProxy("NetTcpBinding_IZzaService");
            //ZzaServiceClient proxy = new ZzaServiceClient("NetTcpBinding_IZzaService");

            try
            {
                //Products = proxy.GetProducts();
                //Customers = proxy.GetCustomers();
                Products = await proxy.GetProductsAsync();
                Customers = await proxy.GetCustomersAsync();
            }
            catch(Exception ex)
            {
                MessageBox.Show("Failed to load server data. " + ex.Message);
            }
            finally
            {
                proxy.Close();
            }
        }
        private void LoadProductsAndCustomers()
        {
            ZzaProxy proxy = new ZzaProxy("NetTcpBinding_IZzaService");
            proxy.ClientCredentials.Windows.ClientCredential.UserName = "******";
            proxy.ClientCredentials.Windows.ClientCredential.Password = "******";
            //ZzaServiceClient proxy = new ZzaServiceClient("NetTcpBinding_IZzaService");
            try
            {
                Products = proxy.GetProducts();
                Customers = proxy.GetCustomers();
 
            }
            catch(Exception ex)
            {
                MessageBox.Show("Failed to load server data. " + ex.Message);
            }
            finally
            {
                proxy.Close();
            }

        }