Display Row Details and Image from GridView on Button click in ASP.Net

I have refer this article

Retrieve-images-using-a-file-path-stored-in-database-in-ASPNet

and done some modification.

HTML:

<form id="form1" runat="server">
    <div>
        <asp:FileUpload ID="FileUpload1" runat="server" />
        <asp:Button ID="btnUpload" runat="server" Text="Upload" OnClick="btnUpload_Click" />
    </div>
    <hr />
    <div>
        <br />
        <asp:ScriptManager runat="server">
        </asp:ScriptManager>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
                <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" Font-Names="Arial">
                    <Columns>
                        <asp:BoundField DataField="ID" HeaderText="ID" />
                        <asp:BoundField DataField="FileName" HeaderText="Image Name" />
                        <%--<asp:ImageField DataImageUrlField="FilePath" ControlStyle-Width="100" ControlStyle-Height="100"
                    HeaderText="Preview Image" />--%>
                        <asp:TemplateField HeaderText="Preview Image">
                            <ItemTemplate>
                                <asp:Image ID="imgPreview" ImageUrl='<%# Eval("FilePath") %>' Width="100" Height="100"
                                    runat="server" />
                            </ItemTemplate>
                        </asp:TemplateField>
                        <asp:TemplateField HeaderText="Get Image">
                            <ItemTemplate>
                                <asp:Button ID="btnGetImage" Text="Get image" runat="server" OnClick="GetImage" />
                            </ItemTemplate>
                        </asp:TemplateField>
                    </Columns>
                </asp:GridView>
                Name of Image
                <asp:TextBox ID="txtDemo" runat="server" />
                <br />
                Image
                <asp:Image ID="imgDemo" runat="server" Width="100" Height="100" Visible="false" />
            </ContentTemplate>
        </asp:UpdatePanel>
    </div>
    </form>

C#:

protected void Page_Load(object sender, EventArgs e)
    {
        DataTable dt = new DataTable();
        String strConnString = System.Configuration.ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
        string strQuery = "select * from FileTable order by ID";
        SqlCommand cmd = new SqlCommand(strQuery);
        SqlConnection con = new SqlConnection(strConnString);
        SqlDataAdapter sda = new SqlDataAdapter();
        cmd.CommandType = CommandType.Text;
        cmd.Connection = con;
        try
        {
            con.Open();
            sda.SelectCommand = cmd;
            sda.Fill(dt);
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }
        finally
        {
            con.Close();
            sda.Dispose();
            con.Dispose();
        }
    }

    protected void GetImage(object sender, EventArgs e)
    {
        GridViewRow row = ((sender as Button).NamingContainer as GridViewRow);
        txtDemo.Text = row.Cells[1].Text;
        this.imgDemo.Visible = true;
        imgDemo.ImageUrl = ((Image)row.FindControl("imgPreview")).ImageUrl;
    }

    protected void btnUpload_Click(object sender, EventArgs e)
    {
        if (FileUpload1.PostedFile != null)
        {
            string FileName = Path.GetFileName(FileUpload1.PostedFile.FileName);

            //Save files to disk
            FileUpload1.SaveAs(Server.MapPath("images/" + FileName));

            //Add Entry to DataBase
            String strConnString = System.Configuration.ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
            SqlConnection con = new SqlConnection(strConnString);
            string strQuery = "insert into FileTable (FileName, FilePath) values(@FileName, @FilePath)";
            SqlCommand cmd = new SqlCommand(strQuery);
            cmd.Parameters.AddWithValue("@FileName", FileName);
            cmd.Parameters.AddWithValue("@FilePath", "images/" + FileName);
            cmd.CommandType = CommandType.Text;
            cmd.Connection = con;
            try
            {
                con.Open();
                cmd.ExecuteNonQuery();
            }
            catch (Exception ex)
            {
                Response.Write(ex.Message);
            }
            finally
            {
                con.Close();
                con.Dispose();
            }
        }
    }

SQL:

CREATE TABLE [dbo].[FileTable](
	[ID] [int] IDENTITY(1,1) NOT NULL,
	[FileName] [varchar](50) NOT NULL,
	[FilePath] [varchar](200) NOT NULL
) ON [PRIMARY]

GO