private FileUploadField AddFileUpLoadElement()
    {
        Ext.Net.FileUploadField newElement = new FileUploadField();
        newElement.ButtonText = "Select FIle";
        newElement.Listeners.FileSelected.Handler = "Z_OldTreatment_YX_X.SyncAddFileUpLoadElement();";
        FormPanel_File1.Items.Add(newElement);
        return newElement;
    }



    [DirectMethod]
    public void SyncAddFileUpLoadElement()
    {
        bool isadd=true;
        foreach (FileUploadField item in FormPanel_File1.Items)
        {
            if (!item.HasFile)
            {
                isadd = false;
                return;
            }
        }
        if (isadd)
        {
            var test = AddFileUpLoadElement();
            test.Render();
        }
    }
                    <ext:FormPanel ID="FormPanel_File1" runat="server" Border="false" Frame="true" AutoRender="true">
                        <Items>
                        </Items>
                    </ext:FormPanel>
when id debug it,FormPanel_File1.Items.count always 1,can i register it to server?please help