Clarification in gridview

  first Gridview

  <asp:GridView ID                ="gvAll" runat="server"
    AutoGenerateColumns           = "false" Font-Names = "Arial"
    Font-Size                     = "11pt" AlternatingRowStyle-BackColor = "#C2D69B"
    HeaderStyle-BackColor         = "green" AllowPaging ="true"
    OnPageIndexChanging           = "OnPaging" PageSize = "10" >
       <Columns>
            <asp:TemplateField>
                <HeaderTemplate>
                    <asp:CheckBox ID      ="chkAll" runat="server" onclick = "checkAll(this);"
                    AutoPostBack          = "true"  OnCheckedChanged = "CheckBox_CheckChanged"/>
                </HeaderTemplate>
                <ItemTemplate>
                    <asp:CheckBox ID      ="chk" runat="server" onclick = "Check_Click(this)"
                    AutoPostBack          = "true"  OnCheckedChanged = "CheckBox_CheckChanged" />
                </ItemTemplate>
            </asp:TemplateField>
            <asp:BoundField DataField     = "ConId" HeaderText = "Customer ID"
             HtmlEncode                   = "false" />
            <asp:BoundField DataField     = "Name" HeaderText = "Contact Name"
            HtmlEncode                    = "false" />
            <asp:BoundField DataField     = "CompanyName" HeaderText = "City"
            HtmlEncode                    = "false" />
       </Columns>
   <AlternatingRowStyle BackColor ="#C2D69B"  />
</asp:GridView>


    Second GridView

<asp:GridView ID                  ="gvSelected" runat="server"
AutoGenerateColumns               = "false" Font-Names = "Arial"
Font-Size                         = "11pt" AlternatingRowStyle-BackColor = "#C2D69B"
HeaderStyle-BackColor             = "green" EmptyDataText = "No Records Selected"  >
<Columns>
    <asp:TemplateField HeaderText ="ID">
        <ItemTemplate>
            <asp:TextBox ID       ="txtid" runat="server" Text='<%#Eval("ConId") %>'></asp:TextBox>
        </ItemTemplate>
    </asp:TemplateField>

    <asp:TemplateField HeaderText ="Name">
        <ItemTemplate>
            <asp:TextBox ID       ="txtid" runat="server" Text='<%#Eval("Name") %>'></asp:TextBox>
        </ItemTemplate>
    </asp:TemplateField>


    <asp:TemplateField HeaderText ="Company">
        <ItemTemplate>
            <asp:TextBox ID       ="txtid" runat="server" Text='<%#Eval("CompanyName") %>'></asp:TextBox>
        </ItemTemplate>
    </asp:TemplateField>

 </Columns>
</asp:GridView>

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

    private void BindPrimaryGrid()
    {
        string constr = ConfigurationManager.ConnectionStrings["ConnectionDB"].ConnectionString;
        //string query = "select CustomerID, ContactName, City from customers";
        string query = "select ConId,Name,CompanyName from Contact";
        SqlConnection con = new SqlConnection(constr);
        SqlDataAdapter sda = new SqlDataAdapter(query, con);
        DataTable dt = new DataTable();
        sda.Fill(dt);
        gvAll.DataSource = dt;
        gvAll.DataBind();  
    }

protected void OnPaging(object sender, GridViewPageEventArgs e)
{
    GetData();
    gvAll.PageIndex = e.NewPageIndex;
    BindPrimaryGrid();
    SetData(); 
}

private void GetData()
{
    DataTable dt;
    if (ViewState["SelectedRecords"] != null)
        dt = (DataTable)ViewState["SelectedRecords"];
    else
        dt = CreateDataTable();
    CheckBox chkAll = (CheckBox)gvAll.HeaderRow
                        .Cells[0].FindControl("chkAll");
    for (int i = 0; i < gvAll.Rows.Count; i++)
    {
        if (chkAll.Checked)
        {
            dt = AddRow(gvAll.Rows[i], dt);
        }
        else
        {
            CheckBox chk = (CheckBox)gvAll.Rows[i]
                            .Cells[0].FindControl("chk");
            if (chk.Checked)
            {
                dt = AddRow(gvAll.Rows[i], dt);
            }
            else
            {
                dt = RemoveRow(gvAll.Rows[i], dt);
            }
        }
    }
    ViewState["SelectedRecords"] = dt;
}

    private void SetData()
    {
        CheckBox chkAll = (CheckBox)gvAll.HeaderRow.Cells[0].FindControl("chkAll");
        chkAll.Checked = true;
        if (ViewState["SelectedRecords"] != null)
        {
            DataTable dt = (DataTable)ViewState["SelectedRecords"];
            for (int i = 0; i < gvAll.Rows.Count; i++)
            {
                CheckBox chk = (CheckBox)gvAll.Rows[i].Cells[0].FindControl("chk");
                if (chk != null)
                {
                    DataRow[] dr = dt.Select("ConId = '" + gvAll.Rows[i].Cells[1].Text + "'");
                    chk.Checked = dr.Length > 0; 
                    if (!chk.Checked)
                    {
                        chkAll.Checked = false;
                    }
                }
            }
        }
    }

private DataTable CreateDataTable()
{
    DataTable dt = new DataTable();
    dt.Columns.Add("ConId");
    dt.Columns.Add("Name");
    dt.Columns.Add("CompanyName");
    dt.AcceptChanges();
    return dt;
}

private DataTable AddRow(GridViewRow gvRow, DataTable dt)
{
    DataRow[] dr = dt.Select("ConId = '" + gvRow.Cells[1].Text + "'");
    if (dr.Length <= 0)
    {
        dt.Rows.Add();
        dt.Rows[dt.Rows.Count - 1]["ConId"] = gvRow.Cells[1].Text;
        dt.Rows[dt.Rows.Count - 1]["Name"] = gvRow.Cells[2].Text;
        dt.Rows[dt.Rows.Count - 1]["CompanyName"] = gvRow.Cells[3].Text;
        dt.AcceptChanges();
    }
    return dt;
}

private DataTable RemoveRow(GridViewRow gvRow, DataTable dt)
{
    DataRow[] dr = dt.Select("ConId = '" + gvRow.Cells[1].Text + "'");
    if (dr.Length > 0)
    {
        dt.Rows.Remove(dr[0]);
        dt.AcceptChanges();
    }
    return dt;
}

protected void CheckBox_CheckChanged(object sender, EventArgs e)
{
    GetData();
    SetData();
    BindSecondaryGrid();
}

private void BindSecondaryGrid()
{
    DataTable dt = (DataTable)ViewState["SelectedRecords"];
    gvSelected.DataSource = dt;
    gvSelected.DataBind(); 
}
}