problem: grid view fired event pageindex changing which wasnt handled

protected void Menu1_MenuItemClick(object sender, MenuEventArgs e)
    {
        DataSet ds = new DataSet();
               
        
        string cs = System.Configuration.ConfigurationManager.ConnectionStrings["connstring"].ConnectionString;
 
        SqlConnection con = new SqlConnection(cs);
        con.Open();
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;
        cmd.CommandText = "SELECT * FROM CONTACT_ENTITIES";
 
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        da.Fill(ds);
 
        //for (i = 0; i <= ds.Tables[0].Rows.Count; i++)
        //{
        //    main.InnerText += ds.Tables[0].Rows[i]["name"].ToString();
        //}
 
        
       GridView1.DataSource = ds;
       GridView1.DataBind();
           
        }
    //public event EventHandler GridViewSortingEventHandler;
 
 
    //void GridView1_Sorting(Object sender, GridViewSortEventArgs e)
    //{
    //    this.GridView1.Sorting += new GridViewSortingEventHandler(this.GridView1_Sorting);
    //}
    protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
    {
             
        
    }