Using a Gridview to display File Directory contents

Hi I need some advice/help with my expandable Gridview. I am trying to map the contents of "c:\inetpub" to a gridview. I have been debugging my code and can see rows being added to my DataTable gvSource but whenever I bind this DT to the Gridview I get the following error:
"Object reference not set to an instance of an object. at gvFiles_RowDataBound(Object sender, GridViewRowEventArgs e)" in particular this line:

var item = e.Row.DataItem as FileSystemItemCS;

item is being set to null

I'll include my code so far:
front end Control code

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="BrowseFilesUsrCtrl.ascx.cs" Inherits="SrvViewingTool.Controls.BrowseFilesUsrCtrl" %>

<table width="100%">
    <tr>
        <td style="width: 631px; removed: static; removed 10px; height: 16px" valign="top">
            <asp:Label ID="lblDateMod" runat="server" EnableViewState="False" Font-Bold="False" Font-Names="Arial Narrow"
                Font-Size="Smaller"></asp:Label></td>
        <td style="width: 1604px; removed: static; height: 16px" valign="top" colspan="2">
            <asp:Label ID="lblFile" runat="server" Font-Bold="False" Font-Names="Arial Narrow" Font-Size="Smaller" EnableViewState="False"></asp:Label></td>
    </tr>
    <tr>
        <td style="width: 371px; removed: static; removed 10px; height: 232px" valign="top" >
           <asp:UpdatePanel ID="Panel1" runat="server">
           <ContentTemplate>
                <asp:GridView ID="gvFiles" runat="server" AutoGenerateColumns="False" 
                    CellPadding="4" ForeColor="#333333" GridLines="None" 
                    onpageindexchanging="gvFiles_PageIndexChanging" 
                    onrowcommand="gvFiles_RowCommand" onrowdatabound="gvFiles_RowDataBound" 
                     Width="370px">
                    <AlternatingRowStyle BackColor="White" Width="700px" Font-Size="Small" />
                    <Columns>
                        <asp:BoundField DataField="FullPath" HeaderText="FileName" SortExpression="FullPath">
                        </asp:BoundField>
                        <asp:TemplateField HeaderText="Name" SortExpression="FullPath">
                            <ItemTemplate>
                                <asp:LinkButton runat="server" ID="lbFolderItem" Text='<%#Eval("FullPath")%>'  
                                CommandName="OpenFolder" CommandArgument='<%# Eval("FullPath") %>' >
                                </asp:LinkButton>
                                <asp:Literal runat="server" ID="ltlFileItem"></asp:Literal>                         
                            </ItemTemplate>
                        </asp:TemplateField>
                        <asp:BoundField DataField="Extention" HeaderText="Ext" SortExpression="Extention">
                        </asp:BoundField>
                        <asp:BoundField DataField="Size" DataFormatString="{0:N0}" HeaderText="Size" HtmlEncode="False"
                            SortExpression="Size">
                            <ItemStyle HorizontalAlign="Right" Wrap="False" />
                        </asp:BoundField>
                        <asp:BoundField DataField="LastWriteTime" DataFormatString="{0:d}" HeaderText="Date Modified"
                            HtmlEncode="False" SortExpression="LastWriteTime">
                            <ItemStyle HorizontalAlign="Right" Wrap="False" />
                        </asp:BoundField>
                    </Columns>
                    <EditRowStyle BackColor="#2461BF" />
                    <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
                    <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
                    <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
                    <RowStyle BackColor="#EFF3FB" />
                    <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />    
                </asp:GridView>
           </ContentTemplate>
           </asp:UpdatePanel>
        </td>
        <td style="width: 100%; removed: static; height: 100%" valign="top">
            <asp:TextBox ID="tbxContents" runat="server" Font-Names="Courier New" Font-Size="Small"
            Height="508px" ReadOnly="True" TextMode="MultiLine" Visible="True" Width="99%"
            Wrap="False" EnableViewState="False"></asp:TextBox>
        </td>
    </tr>
</table>
<asp:HiddenField ID="HiddenField1" runat="server" />

CodeBehind Control

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

        void Page_PreRender(object sender, EventArgs e)
        {
            if (IsPostBack)
            {
                if(DirPath!="None")
                    PopulateGrid();   
            }
        }

        public override void DataBind()
        {
            if (DirPath != "None")
                PopulateGrid();
        }

        protected void PopulateGrid()
        {
            try
            {
                DataTable gvSource = DisplayFilesInGridView();
                DataRow gvRow;

                //Get All Folders Or Directories and add in table
                DirectoryInfo directory = new DirectoryInfo(@DirPath);//(@"c:\inetpub");
                DirectoryInfo[] subDirectories = directory.GetDirectories();
                foreach (DirectoryInfo dirInfo in subDirectories)
                {
                    gvRow = gvSource.NewRow();
                    gvRow["FullPath"] = dirInfo.Name;
                    gvRow["Extention"] = "Directory";
                    gvRow["Size"] = 0;
                    gvRow["LastWriteTime"] = dirInfo.LastWriteTime;
                    gvRow["IsFolder"] = 1;
                    gvRow["ImageUrl"] = @"~\Images\Folder.gif";
                    gvSource.Rows.Add(gvRow);                    
                }

                //Get files in all directories 
                FileInfo[] files = directory.GetFiles("*.*", SearchOption.AllDirectories);
                foreach (FileInfo fileInfo in files)
                {
                    bool canView = false;
                    try
                    {
                        string ext = ConfigurationManager.AppSettings["ViewExt"];
                        string[] extensions = ext.Split(';');
                        foreach (string extension in extensions)
                        {
                            if (String.Compare(fileInfo.Extension, extension, true) == 0)
                            {
                                canView = true;
                                break;
                            }
                        }
                    }
                    catch (Exception)
                    {
                    }

                    if (canView)
                    {
                        gvRow = gvSource.NewRow();
                        gvRow["FullPath"] = fileInfo.Name;
                        gvRow["Size"] = fileInfo.Length;
                        gvRow["Extention"] = "File";
                        gvRow["LastWriteTime"] = fileInfo.LastWriteTime;
                        gvRow["IsFolder"] = 0;
                        //could do a switch to get correct image for each file type
                        switch (fileInfo.Extension)
                        {
                            case ".txt":
                            case ".log":
                                gvRow["ImageUrl"] = @"~\Images\page.gif";
                                break;
                            case ".bat":
                                gvRow["ImageUrl"] = @"~\Images\BAT.ico";
                                break;
                            case ".ini":
                                gvRow["ImageUrl"] = @"~\Images\INI.ico";
                                break;
                            case ".config":
                                gvRow["ImageUrl"] = @"~\Images\XML.ico";
                                break;
                            case ".aspx":
                                gvRow["ImageUrl"] = @"~\Images\ASPX.gif";
                                break;
                            case ".xml":
                                gvRow["ImageUrl"] = @"~\Images\XML.ico";
                                break;
                            default:
                                gvRow["ImageUrl"] = @"~\Images\page.gif";
                                break;
                        }
                        //gvRow["ImageUrl"] = @"~\Images\Windows.gif";
                        gvSource.Rows.Add(gvRow);
                    }
                    else if (String.Compare(fileInfo.Extension, ".exe", true) == 0 ||
                            String.Compare(fileInfo.Extension, ".dll", true) == 0)
                    {
                        //tbxContents.Text = String.Format("Version:\t{0}\nDateModified:\t{1}\nSize(bytes):\t{2}",
                        //    System.Diagnostics.FileVersionInfo.GetVersionInfo(node.Value).ProductVersion,
                        //    dt.ToLocalTime().ToString(), fi.Length);
                        //lblFile.Text = node.Value + "  [Date Modified: " + dt.ToLocalTime().ToString() + "]";
                        ShowEdit(true);
                    }
                    else
                    {
                        lblDateMod.Text = "Current File/Dir Last Modified on: " + fileInfo.LastWriteTimeUtc.ToString();
                        ShowEdit(false);
                    }
                }


                gvFiles.DataSource = gvSource;
                gvFiles.DataBind();
            }
            catch (Exception ex)
            {
                tbxContents.Text = ex.Message;
            }
        }

        private DataTable DisplayFilesInGridView()
        {
            DataTable dtGvSource = new DataTable();
            dtGvSource.Columns.Add("FullPath", typeof(String));
            dtGvSource.Columns.Add("Extention", typeof(String));
            dtGvSource.Columns.Add("size", typeof(Int32));
            dtGvSource.Columns.Add("LastWriteTime", typeof(DateTime));
            dtGvSource.Columns.Add("IsFolder", typeof(Boolean));
            dtGvSource.Columns.Add("ImageUrl", typeof(String));            
            return dtGvSource;
        }

protected void gvFiles_PageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            gvFiles.PageIndex = e.NewPageIndex;

            PopulateGrid();
        }

        protected void gvFiles_RowCommand(object sender, GridViewCommandEventArgs e)
        {
            if (e.CommandName == "OpenFolder")
            {
                if (string.CompareOrdinal(e.CommandArgument.ToString(), "..") == 0)
                {
                    var currentFullPath = this.CurrentFolder;
                    if (currentFullPath.EndsWith("\\") || currentFullPath.EndsWith("/"))
                        currentFullPath = currentFullPath.Substring(0, currentFullPath.Length - 1);

                    currentFullPath = currentFullPath.Replace("/", "\\");

                    var folders = currentFullPath.Split("\\".ToCharArray());

                    this.CurrentFolder = string.Join("\\", folders, 0, folders.Length - 1);
                }
                else
                    this.CurrentFolder = Path.Combine(this.CurrentFolder, e.CommandArgument as string);


                PopulateGrid();
            }
        }

        protected void gvFiles_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            if (e.Row.RowType == DataControlRowType.DataRow)
            {
                var item = e.Row.DataItem as FileSystemItemCS;

                if (item.IsFolder)
                {
                    var lbFolderItem = e.Row.FindControl("lbFolderItem") as LinkButton;
                    lbFolderItem.Text = string.Format(@"<img src=""{0}"" alt="""" /> {1}", Page.ResolveClientUrl("~/Images/folder.png"), item.Name);
                }
                else
                {
                    var ltlFileItem = e.Row.FindControl("ltlFileItem") as Literal;
                    if (this.CurrentFolder.StartsWith("~"))
                        ltlFileItem.Text = string.Format(@"<a href=""{0}"" target=""_blank"">{1}</a>",
                                Page.ResolveClientUrl(string.Concat(this.CurrentFolder, "/", item.Name).Replace("//", "/")),
                                item.Name);
                    else
                        ltlFileItem.Text = item.Name;
                }
            }
        }

FileSystemItemCS.cs

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace SrvViewingTool
{
    public class FileSystemItemCS
    {
        public FileSystemItemCS(FileInfo file)
        {
            this.Name = file.Name;
            this.FullName = file.FullName;
            this.Size = file.Length;
            this.CreationTime = file.CreationTime;
            this.LastAccessTime = file.LastAccessTime;
            this.LastWriteTime = file.LastWriteTime;
            this.IsFolder = false;
        }

        public FileSystemItemCS(DirectoryInfo folder)
        {
            this.Name = folder.Name;
            this.FullName = folder.FullName;
            this.Size = null;
            this.CreationTime = folder.CreationTime;
            this.LastAccessTime = folder.LastAccessTime;
            this.LastWriteTime = folder.LastWriteTime;
            this.IsFolder = true;
        }

        public string Name { get; set; }
        public string FullName { get; set; }
        public long? Size { get; set; }
        public DateTime CreationTime { get; set; }
        public DateTime LastAccessTime { get; set; }
        public DateTime LastWriteTime { get; set; }
        public bool IsFolder { get; set; }

        public string FileSystemType
        {
            get
            {
                if (this.IsFolder)
                    return "File folder";
                else
                {
                    var extension = Path.GetExtension(this.Name);

                    if (IsMatch(extension, ".txt"))
                        return "Text file";
                    else if (IsMatch(extension, ".pdf"))
                        return "PDF file";
                    else if (IsMatch(extension, ".doc", ".docx"))
                        return "Microsoft Word document";
                    else if (IsMatch(extension, ".xls", ".xlsx"))
                        return "Microsoft Excel document";
                    else if (IsMatch(extension, ".jpg", ".jpeg"))
                        return "JPEG image file";
                    else if (IsMatch(extension, ".gif"))
                        return "GIF image file";
                    else if (IsMatch(extension, ".png"))
                        return "PNG image file";


                    // If we reach here, return the name of the extension
                    if (string.IsNullOrEmpty(extension))
                        return "Unknown file type";
                    else
                        return extension.Substring(1).ToUpper() + " file";
                }
            }
        }

        private bool IsMatch(string extension, params string[] extensionsToCheck)
        {
            foreach (var str in extensionsToCheck)
                if (string.CompareOrdinal(extension, str) == 0)
                    return true;

            // If we reach here, no match
            return false;
        }
    }
}

Tags: C#, ASP.NET, Gridview