ASP.Net GridView Row Deleting Error: Index was out of range. Must be non-negative and less than the size of the collection

When i am updating row in gridview then this error is coming 

index was out of range.Kindly help .

i am getting this error on this code

Index was out of range. Must be non-negative and less than the size of the collection.

int customerId = Convert.ToInt32(GridView1.DataKeys[e.RowIndex].Values[0]);

            protected void GridView1_RowDeleting(object sender, GridViewDeleteEventArgs e)
            {
                int customerId = Convert.ToInt32(GridView1.DataKeys[e.RowIndex].Values[0]);
                string query = "DELETE FROM Customers WHERE CustomerId=@CustomerId";
                string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
                using (SqlConnection con = new SqlConnection(constr))
                {
                    using (SqlCommand cmd = new SqlCommand(query))
                    {
                        cmd.Parameters.AddWithValue("@CustomerId", customerId);
                        cmd.Connection = con;
                        con.Open();
                        cmd.ExecuteNonQuery();
                        con.Close();
                    }
                }
                GridView1.EditIndex = -1;
                this.BindGrid();
            }