ช่วยดู code WPF ให้หน่อยครับ เกี่ยวกับ class ItemContainerGenerator.ContainerFromItem ผมใช้แล้วมันได้แต่ค่า null อะครับ

        private void IsvProductList_Drop(object sender, DragEventArgs e)
        {
            tempdata = (string[])(e.Data.GetData(DataFormats.Text, true));
            ListViewItem lvi = (ListViewItem)IsvProductList.ItemContainerGenerator.ContainerFromItem(tempdata);
            IsvProductList.Items.Add(lvi);
            Array.Clear(tempdata, 0, tempdata.Length);
        }

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
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 Microsoft.Windows.Controls;
using Drewsn32Biz.DataBase;
using Microsoft.Windows.Controls.Primitives;
using System.Reflection;
using System.ComponentModel;
using System.Windows.Controls.Primitives;
using System.Data;
namespace Drewsn32Biz
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        DataBase.dbDrewsn32BizDataContext db = new DataBase.dbDrewsn32BizDataContext();
        string[] tempdata = new string[4];
        public MainWindow()
        {
            InitializeComponent();
            IsvProductList.Drop += new DragEventHandler(IsvProductList_Drop);
            dgvProductList.MouseMove += new MouseEventHandler(dgvProductList_MouseMove);

        }
        private void Grid_Loaded(object sender, RoutedEventArgs e)
        {
            var cs = from c in db.UserNames
                     select new
                     {
                         UserID = c.UserName1,
                         Password = c.Password,
                         IsNormal = c.IsNormal,
                         HumanID = c.HID
                     };
            if (cs.Count() > 0)
            {
                dgvProductList.ItemsSource = cs.ToList();
                GridView gv = new GridView();
                GridViewColumn gvc = new GridViewColumn();
                gvc.Header = "UserID";
                gvc.Width = Double.NaN;
                gv.Columns.Add(gvc);
                GridViewColumn gvc1 = new GridViewColumn();
                gvc1.Header = "Password";
                gvc1.Width = Double.NaN;
                gv.Columns.Add(gvc1);
                GridViewColumn gvc2 = new GridViewColumn();
                gvc2.Header = "IsNormal";
                gvc2.Width = Double.NaN;
                gv.Columns.Add(gvc2);
                GridViewColumn gvc3 = new GridViewColumn();
                gvc3.Header = "HumanID";
                gvc3.Width = Double.NaN;
                gv.Columns.Add(gvc3);
                // Setup the GridView Columns
                IsvProductList.View = gv;
                // Display the Data


            }
            else
            {
                dgvProductList.ItemsSource = null;
            }
        }

        private void IsvProductList_Drop(object sender, DragEventArgs e)
        {
            tempdata = (string[])(e.Data.GetData(DataFormats.Text, true));
            ListViewItem lvi = (ListViewItem)IsvProductList.ItemContainerGenerator.ContainerFromItem(tempdata);
            IsvProductList.Items.Add(lvi);
            Array.Clear(tempdata, 0, tempdata.Length);
        }
        private void ShowLogin()
        {
            this.Hide();
            Login log = new Login();
            log.Owner = this;
            log.ShowDialog();
            //ถ้า From MainLogin ส่งค่า DialogResult = true มาให้ทำ if
            if (log.DialogResult.HasValue && log.DialogResult.Value)
            {
                this.Show();
                return;
            }
            else
            {
                this.Close();
            }
        }
        private void dgvProductList_MouseMove(object sender, MouseEventArgs e)
        {
            #region Algorithum Check Row
            DependencyObject dep = (DependencyObject)e.OriginalSource;
            while ((dep != null) && !(dep is DataGridCell) && !(dep is DataGridColumnHeader))
            {
                dep = VisualTreeHelper.GetParent(dep);
            }

            if (dep == null)
                return;
            if (dep is DataGridCell)
            {
                // navigate further up the tree
                while ((dep != null) && !(dep is DataGridRow))
                {
                    dep = VisualTreeHelper.GetParent(dep);
                }
                if (dep == null)
                    return;
                try
                {
                    int count = 0;
                    string data = "";
                    foreach (var dataGridCellInfo in dgvProductList.SelectedCells)
                    {
                        PropertyInfo pi = dataGridCellInfo.Item.GetType().GetProperty(Convert.ToString(dataGridCellInfo.Column.Header));
                        var temp = Convert.ToString(pi.GetValue(dataGridCellInfo.Item, null));
                        data += temp;
                        tempdata[count] = Convert.ToString(temp);
                        count += +1;
                    }
                    textBox2.Text = data;
                    t1.Text = tempdata[0].ToString();
                    t2.Text = tempdata[1].ToString();
                    t3.Text = tempdata[2].ToString();
                    t4.Text = tempdata[3].ToString();

                }
                catch (Exception)
                {
                    return;
                }
            }
            #endregion
            if (e.LeftButton == MouseButtonState.Pressed)
            {
                DragDropEffects dds;
                DataObject AnyData;
                AnyData = new DataObject();
                AnyData.SetData(DataFormats.Text, tempdata);
                dds = DragDrop.DoDragDrop(dgvProductList, AnyData, DragDropEffects.Copy);
            }
        }
    }
}