doubt in detail view

Question

Customer Code

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;

public partial class _Default : System.Web.UI.Page
{
    SqlConnection con = new SqlConnection("Server=(local);initial catalog=Master;Trusted_Connection=True");
    SqlCommand cmd;
    string str;
    int count;

    SqlDataAdapter sqlda;
    DataSet ds;
    protected void Page_Load(object sender, EventArgs e)
    {

        if (!IsPostBack)
        {
            FillDropdown();
        }
    }
    void FillDropdown()
    {

        cb_DropDownList1.Items.Add("choose");
            con.Open();
            str = "select * from customerdetails";
            cmd = new SqlCommand(str, con);
            SqlDataReader reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                cb_DropDownList1.Items.Add(reader["Companyid"].ToString());
            }
            reader.Close();
            con.Close();
        }
   
    protected void btn_new_Click(object sender, EventArgs e)
    {
        str = "select count(*) from customerdetails";
        cmd = new SqlCommand(str, con);
        con.Open();
        count = Convert.ToInt16(cmd.ExecuteScalar()) + 1;
        cb_DropDownList1.Items.Add("C0000" + count);
      
        con.Close();
    }
    protected void btn_save_Click(object sender, EventArgs e)
    {
        con.Open();
        str = "insert into customerdetails values (' " + cb_DropDownList1.SelectedItem.Text + "',' " + txt_comname.Text + "',' " + txt_address.Text + "',' " + cb_area.Text + "',' " + txt_city.Text + "',' " + txt_state.Text + "', " + txt_phone.Text + ", " + txt_pincode.Text + ", " + txt_mobileno.Text + ", '" + txt_email.Text + "',' " + txt_contactperson.Text + "', ' " + cb_status.Text + "')";
        cmd = new SqlCommand(str, con);
        Response.Write("Record Inserted successfully");
        cmd.ExecuteNonQuery();
        con.Close();
    }
    protected void btn_update_Click(object sender, EventArgs e)
    {
        con.Open();
        SqlCommand cmd = new SqlCommand("update customerdetails  phone ' " + txt_phone.Text + "' where Companyid =' " + cb_DropDownList1.SelectedItem.Text + "'", con);
        cmd.ExecuteNonQuery();
        Response.Write("record updated successfully");
        SqlCommand cmd1 = new SqlCommand("select * from customerdetails", con);
        SqlDataAdapter adp = new SqlDataAdapter(cmd1);
        DataSet ds = new DataSet();
        adp.Fill(ds);
        con.Close();



    }
    protected void btn_delete_Click(object sender, EventArgs e)
    {

    }
    protected void cb_DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
       


        con.Open();
        str = "select * from customerdetails where Companyid like ' " + cb_DropDownList1.SelectedItem.Text + "% '";
        cmd = new SqlCommand(str, con);
        sqlda = new SqlDataAdapter(cmd);
        ds = new DataSet();
        sqlda.Fill(ds, "customerdetails");
        con.Close();
        DetailsView1.DataSource = ds;
        DetailsView1.DataBind();
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        //cb_DropDownList1.Text = "";
        txt_comname.Text = "";
        txt_address.Text = "";
        cb_area.Text = "";
        txt_city.Text = "";
        txt_state.Text = "";
        txt_phone.Text = "";
        txt_pincode.Text = "";
        txt_mobileno.Text = "";
        txt_email.Text = "";
        txt_contactperson.Text = "";
        cb_status.Text ="";


    }
}



when i click the dropdown in comapny id the corresponding id details will not be displayed in detail view.kindly please help me.help me please urgent