Add new row in table in code behind problem

I have table on my asp.net page, and I want to insert new rows.I try to add on every click on button new row which contain cell with FileUpload, but it works only for first time. When I click next time, in my code behind table.

    <asp:Panel ID="pnlImages" runat="server" BackColor="Gray" Height="500">
      <table id="tblImages" runat="server" width="100%">
        <tr>
          <td>
            <asp:FileUpload ID="FileUpload1" runat="server" />
          </td>
       </tr>
       <tr>
          <td align="right" width="100">
            <asp:ImageButton ID="imbAddImage" runat="server" ImageUrl="images/plus.png" 
                  Width="48" Height="48"  OnClick="imbAddImage_Click"/>
         </td>
      </tr>
    </table>
</asp:Panel>

This is code on button click

protected void imbAddImage_Click(object sender, ImageClickEventArgs e)
{
    System.Web.UI.HtmlControls.HtmlTable tbl = (System.Web.UI.HtmlControls.HtmlTable)this.FindControl("tblImages");
    System.Web.UI.HtmlControls.HtmlTableRow row = new System.Web.UI.HtmlControls.HtmlTableRow();
    System.Web.UI.HtmlControls.HtmlTableCell cell = new System.Web.UI.HtmlControls.HtmlTableCell();
    FileUpload temp = new FileUpload();
    cel开发者_Go百科l.Controls.Add(temp);
    row.Controls.Add(cell); ;
    int a=tbl.Controls.Count;
    tbl.Controls.AddAt(a-1, row);
}

But problem is that a is always 2. Can anybody help ?

When it comes to dynamic controls, you need to add them on every post back.

You click event handler only adds the newest file and you are not saving the previous ones anywhere. You should add them to the ViewState and query the ViewState to retrieve them.

See this article For a detailed explanation of ViewState.