Filter GridView using TextBox and Paging in GridView ASP.Net

Please refer this example

Ref:Search Filter GridView Records based on TextBox in ASP.Net

HTML

<form id="form1" runat="server">
<div>
Id:
<asp:TextBox ID="txtSearch" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="Search" OnClick = "Search" />
<br />
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns = "false" OnPageIndexChanging="GridView1_OnPageIndexChanging" PageSize="3" AllowPaging="true">
    <Columns>
        <asp:BoundField DataField="CustomerId" HeaderText="Contact Id" />
        <asp:BoundField DataField="ContactName" HeaderText="Contact Id" />
        <asp:BoundField DataField="Country" HeaderText="Country" />
    </Columns>
</asp:GridView>
</div>
</form>

Namespace

using System.Configuration;
using System.Data.SqlClient;
using System.Data;

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        BindGrid();
    }
}

protected void Search(object sender, EventArgs e)
{
    this.BindGrid();
}

private void BindGrid()
{
    string conString = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
    string query = "SELECT * FROM Customers";

    string id = txtSearch.Text.Trim();
    if (!string.IsNullOrEmpty(id))
    {
        id = string.Format(" where Country = '{0}'", id);
    }
    SqlCommand cmd = new SqlCommand(query + id);
    using (SqlConnection con = new SqlConnection(conString))
    {
        using (SqlDataAdapter sda = new SqlDataAdapter())
        {
            cmd.Connection = con;

            sda.SelectCommand = cmd;
            using (DataSet ds = new DataSet())
            {
                sda.Fill(ds);
                GridView1.DataSource = ds;
                GridView1.DataBind();
            }
        }
    }
}

protected void GridView1_OnPageIndexChanging(object sender, GridViewPageEventArgs e)
{
    this.GridView1.PageIndex = e.NewPageIndex;
    this.BindGrid();
}