iam trying to insert values in gridview but not getting

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace treeview_grossalary
{
    public partial class Form1 : Form
    {
        SqlConnection con = new SqlConnection("Data Source=CIODEV03\\SQLEXPRESS;Initial Catalog=EmployeeDB;Integrated Security=True");
        SqlCommand cmd = new SqlCommand();

       public Form1()
        {
            InitializeComponent();
        }

       private void Form1_Load(object sender, EventArgs e)
       {
           getdata();
       }
        private void getdata()
        {
            string str = "select * from gridsalry";
            SqlDataAdapter ada = new SqlDataAdapter(str, con);
            DataSet ds = new DataSet();
            ada.Fill(ds, "X");
            dataGridView1.DataSource = ds.Tables[0];
        }

        private void btnsave_Click(object sender, EventArgs e)
        {
            string str = "insert into gridsalry values('" + textBox1.Text + "','" +textBox2.Text+ "','" + textBox3.Text +      "','"+textBox4.Text+"','"+textBox5.Text+"','"+textBox6.Text+"','"+textBox7.Text+"','"+textBox8.Text+"')";
            con.Open();
            cmd = new SqlCommand(str, con);
            cmd.ExecuteNonQuery();
            con.Close();
        }