How to display file in gridview from folder

<form id="form1" runat="server">
    <div>
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
    </div>
    <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />
    <br />
    <asp:GridView ID="GridView1" runat="server">
    </asp:GridView>
</form>

protected void Button1_Click(object sender, EventArgs e)
{
    DataTable dt = new DataTable("Mydata");
    dt.Columns.Add("ID", typeof(int));
    dt.Columns.Add("File", typeof(string));
    dt.Columns.Add("Folder", typeof(string));
    dt.Columns["ID"].AutoIncrement = true;
    dt.Columns["ID"].AutoIncrementSeed = 1;
    dt.Columns["ID"].AutoIncrementStep = 1;

    ProcessDirectory(TextBox1.Text.Trim(), ref dt);
    GridView1.DataSource = dt;
    GridView1.DataBind();
}
public void ProcessDirectory(string targetDirectory, ref DataTable dt)
{
    string[] fileEntries = Directory.GetFiles(targetDirectory);
    foreach (string fileName in fileEntries)
    {
        FileInfo fi = new FileInfo(fileName);
        dt.Rows.Add(null, fi.Name, targetDirectory);
    }
    string[] subdirectoryEntries = Directory.GetDirectories(targetDirectory);
    foreach (string subdirectory in subdirectoryEntries)
    {
        ProcessDirectory(subdirectory, ref dt);
    }
}