using System;
using System.Collections.Generic;
using System.Linq;
using System.Data;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using Telerik.Windows.Controls;
using Telerik.Windows.Controls.GridView;
using Telerik.Windows.Data;

namespace TestTelerikQ2
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            try
            {
                InitializeComponent();

                GridViewFooterCell g;
               
                GridViewFooterRow footerRow = new GridViewFooterRow();

                Telerik.Windows.Data.SumFunction sum = new SumFunction();

                sum.Caption = "sum: ";

                sum.ResultFormatString = "{}{0:c}";

                sum.SourceField = "Number";

                Telerik.Windows.Controls.GridViewDataColumn column =
                        (Telerik.Windows.Controls.GridViewDataColumn)radGridView1.Columns["Number"];

                //column.Footer = footerRow;

                DataTable dt = new DataTable();
                DataView dv;

                dt.Columns.Add("Display", typeof(string));
                dt.Columns.Add("Number", typeof(int));

                dt.Rows.Add("show", 1);
                dt.Rows.Add("show", 2);
                dt.Rows.Add("hide", 3);

                dv = new DataView(dt);

                radGridView1.ItemsSource = dv;

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }

                       
        }

    }
}

<Window x:Class="WpfToTelerikForum.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="333" Width="639" xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation">
    <StackPanel Orientation="Vertical">
        <telerik:RadGridView Margin="12,20,-12,-20"
                             Name="radGridView1"
                             Loaded="radGridView1_Loaded" />
        <Button Margin="8" Height="50" Width="50" Content="ClickMe" Click="Button_Click"/>
    </StackPanel>
</Window>

using System;
using System.Data;
using System.Windows;
using System.Windows.Controls;
using Telerik.Windows.Controls;
using Telerik.Windows.Controls.GridView;
using Telerik.Windows.Data;

namespace WpfToTelerikForum
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        private void radGridView1_Loaded(object sender, RoutedEventArgs e)
        {
            DataTable dt = new DataTable();
            DataView dv;

            dt.Columns.Add("Display", typeof(string));
            dt.Columns.Add("Number", typeof(int));

            dt.Rows.Add("show", 1);
            dt.Rows.Add("show", 2);
            dt.Rows.Add("hide", 3);

            dv = new DataView(dt);

            dv.RowFilter = "Display = 'show'";

            radGridView1.ItemsSource = dv;

        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            DataTable dt;
            DataView dv;

            dv = ((DataView)radGridView1.ItemsSource);
            dt = dv.Table;

            dt.Rows[dt.Rows.Count-1]["Display"] = "show";

            radGridView1.Records[radGridView1.Records.Count-1].IsSelected = true;
        }
    }
}