Add and reload new items in the listbox

We will know how to insert records to database and show one column of inserted items into a listbox.Here we use two textboxes, button and a listbox.And after adding items it is automatically loaded to the listbox.

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 After_add_new_item_reload_listbox
{
    public partial class Form1 : Form
    {
        SqlConnection con = new SqlConnection(@"server = HOME-SAT/SQLEXPRESS;data source = .; initial catalog = test; user id=sa;pwd =pintu ;integrated security = SSPI");
        SqlCommand com;
        SqlDataAdapter sqlda;
        DataSet ds;
        string str;
        DataTable dt;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            listboxbind();
        }

        private void listboxbind()
        {
            con.Open();
            str = "select * from employee";
            com = new SqlCommand(str, con);
            sqlda = new SqlDataAdapter(com);
            ds = new DataSet();
            sqlda.Fill(ds, "employee");
            dt = ds.Tables["employee"];
            listBox1.DisplayMember = "empid";
            listBox1.ValueMember = "empname";
            listBox1.DataSource = ds.Tables["employee"];
            con.Close();
        }

        private void btn_add_Click(object sender, EventArgs e)
        {
            com = new SqlCommand();
            com.Connection = con;
            com.CommandType = CommandType.Text;
            com.CommandText = "insert into employee values(@empid,@empname)";
            com.Parameters.Clear();
            com.Parameters.AddWithValue("@empid", txt_id.Text);
            com.Parameters.AddWithValue("@empname", txt_name.Text);
            if (con.State == ConnectionState.Closed)
                con.Open();
            com.ExecuteNonQuery();
            con.Close();
            MessageBox.Show("Data entered successfully!!!");
            listboxbind();
            clear();
        }

        private void clear()
        {
            txt_id.Text = "";
            txt_name.Text="";
        }
    }
}