Asp.net how to use validation control code

Actually im designing my web page, in that i have typed in the book id and

Nameofthebook. typed and then click the button the book are available is go to another page and then not available is display the error message is book is not available My project (Library management system) Asp.net sql server how to validate the page and how to set validate control and how to set validate control code... send me full details

My code
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;


public partial class Bookcheck : System.Web.UI.Page
{
      public Int64 Sid;
    protected void Page_Load(object sender, EventArgs e)
    {
        string Id;
 开发者_运维知识库       Id = Request.QueryString.Get(0);

    if (!(IsPostBack == true))
    {
        if (Request.QueryString.Get(1) == "G")
        {
            Sid = Convert.ToInt64(Id);
            if (PopulatedRecord (Sid ) == false)
            {

            }
        }
    }
}
private Boolean PopulatedRecord(Int64 Id)
{
    DataSet DS;
    DS = new DataSet();
    SqlCommand cmd = new SqlCommand();
    SqlDataAdapter da = new SqlDataAdapter();
    SqlConnection Cnn = new SqlConnection();
    string connectionstring;
    connectionstring = @"Datasource=DEVI\SQLEXPRESS;Intial catalog=librarymanagement;Integrated Security=SSPI";
    Cnn.ConnectionString = connectionstring;
    if (Cnn.State != ConnectionState.Open)
        Cnn.Open();
    cmd.Connection = Cnn;
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.CommandText = "usbinsertdatainto";
    cmd.Parameters.Clear();
    cmd.Parameters.AddWithValue("@bookId",txtid );
    da.SelectCommand = cmd;
    try
    {
        da.Fill(DS);
    }
    catch (Exception ex)
    {
        throw new ApplicationException(
            "!!! An Error Occured While Update Record In Dtl_SecurityCapital_Upload." + ex.Message);
        lblerror.Visible = true;
        lblerror.Text = "!!! An Error Occured While " + ex.Message.ToString();
        return false;
    }
    if (DS.Tables[0].Rows.Count > 0)
    {
        txtid.Text = DS.Tables[0].Rows[0]["bookId"].ToString();
        txtnb.Text = DS.Tables[0].Rows[0]["Nameofthebook"].ToString();
    }
    cmd.Dispose();
    Cnn.Close();
    Cnn.Dispose();
    return true;
}


}
        protected void  Button2_Click(object sender, EventArgs e)
         {
        if(Page.IsValid )
        {
        Response.Redirect ("issueofbook.aspx?bookid="+txtid.Text  

                                             +"&Nameofthebook="+txtnb.Text);
          }
      }
    }      

                   Error
                               Line 59:             throw new ApplicationException(
                               Line 60:                 "!!! An Error Occured While  
                                                      Update                              

                               Record In Dtl_SecurityCapital_Upload." + ex.Message);
                                Line 61:             lblerror.Visible = true;
                                   Line 62:             lblerror.Text = "!!! An Error 
                                                Occured While " +                          
                                                             ex.Message.ToString();

Line 63: return false;

Dear, Use RequiredFieldValidator (ASP.NET control) for checking TextBox are empty or not. or use JavaScript to check Textbox is empty or not

Markup:

<asp:TextBox ID="txtNo" runat="server" />
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server"  ErrorMessage="No Required " ControlToValidate="txtNo" />
<asp:TextBox ID="txtName" runat="server"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ErrorMessage="Name Required " ControlToValidate="txtName" />
<asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />

Button click event :

protected void Button1_Click(object sender, EventArgs e)
{
    if (Page.IsValid)
    {
        Response.Redirect("~/Newpage.aspx?no=" + txtNo.Text + "&name=" + txtName.Text); 
    }
}