c#写入数据库，对象的实例

我正在编程我的第一个c#应用程序，它必须连接到数据库。我想保存数据从文本框到数据库，但我有问题在标记行。

连接数据库代码:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace prviTelefonskiImenik
{
    class DatabaseConnection
    {
        private string sql_string;
        private string strCon;
        System.Data.SqlClient.SqlDataAdapter da_1;
        public string Sql
        {
            set { sql_string = value; }
        }
        public string connection_string
        {
            set { strCon = value; }
        }
        public System.Data.DataSet GetConnection
        {
            get 
            { return MyDataSet(); }
        }
        private System.Data.DataSet MyDataSet()
        {
            System.Data.SqlClient.SqlConnection con = new System.Data.SqlClient.SqlConnection(strCon);
            con.Open();
            da_1 = new System.Data.SqlClient.SqlDataAdapter(sql_string, con);
            System.Data.DataSet dat_set = new System.Data.DataSet();
            da_1.Fill(dat_set, "Table_Data_1");
            //da_1.Fill(dat_set, "kontakti");
            con.Close();
            return dat_set;
        }
        public void UpdateDatabase(System.Data.DataSet ds)
        {
            System.Data.SqlClient.SqlCommandBuilder cb = new System.Data.SqlClient.SqlCommandBuilder(da_1);
            cb.DataAdapter.Update(ds.Tables[0]);
        }
    }
}

以及将数据从textbox保存到数据库的代码:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace prviTelefonskiImenik
{
    public partial class dodajKontakt : Form
    {
        public dodajKontakt()
        {
            InitializeComponent();
        }
        DatabaseConnection objConnect;
        string conString;
        DataSet ds;
        DataRow dRow;
        int MaxRows;
        int inc = 0;
        private void dodajKontakt_Load(object sender, EventArgs e)
        {
            try
            {
                objConnect = new DatabaseConnection();
                conString = Properties.Settings.Default.kontaktiConnectionString;
                objConnect.connection_string = conString;
                objConnect.Sql = Properties.Settings.Default.SQL;
                ds = objConnect.GetConnection;
                MaxRows = ds.Tables[0].Rows.Count;
                NavigateRecords();
            }
            catch (Exception err)
            {
                MessageBox.Show(err.Message);
            }
        }
        private void NavigateRecords()
        {
            dRow = ds.Tables[0].Rows[inc];
            txtIme.Text = dRow.ItemArray.GetValue(1).ToString();
            txtPriimek.Text = dRow.ItemArray.GetValue(2).ToString();
            txtEmso.Text = dRow.ItemArray.GetValue(3).ToString();
            txtTelefon.Text = dRow.ItemArray.GetValue(4).ToString();
            txtEmail.Text = dRow.ItemArray.GetValue(5).ToString();
        }
        private void shrani_Click(object sender, EventArgs e)
        {
            **DataRow row = ds.Tables[0].NewRow();**
            row[1] = txtIme.Text;
            row[2] = txtPriimek.Text;
            row[3] = txtEmso.Text;
            row[4] = txtTelefon.Text;
            row[5] = txtEmail.Text;
            ds.Tables[0].Rows.Add(row);
            try
            {
                objConnect.UpdateDatabase(ds);
                MaxRows = MaxRows + 1;
                inc = MaxRows - 1;
                MessageBox.Show("Database updated");
            }
            catch (Exception err)
            {
                MessageBox.Show(err.Message);
            }
        }
    }
}

编译时，Visual Studio 2013在这里发现一个错误:DataRow row = ds.Tables[0].NewRow();附加信息:对象引用未设置为对象的实例。

你能帮我解决一个问题吗?谢谢!

if(ds!= null && ds.Tables.Count> 0)
{
DataRow row = ds.Tables[0].NewRow();
}