Problem loading states of server controls residing in user control

Question

I have user control which contains two text boxes and two dropdown list. I am loading this control first time on page_load event programatically. After that on each button click event of "Add New" button, controls are added dynamically but when this happens, previously loaded controls are showing all server controls(which are inside user control) empty. How can i retain the state of these controls? My user control code is as shown below.

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="qualificationControl.ascx.cs" Inherits="qualificationControl" %>
<style type="text/css">

.RowHeight
{
    height: 30px;
}
</style>
<table width="100%">
    <tr>
        <td class="RowHeight" width="20%">
            Course Name</td>
        <td width="20%">
            <asp:DropDownList ID="courseList" runat="server" Width="100px">
            </asp:DropDownList>
        </td>
        <td width="20%">
            Year of Passing</td>
        <td width="*">
            <asp:DropDownList ID="yearList" runat="server" Width="100px">
                <asp:ListItem Value="0">2005</asp:ListItem>
                <asp:ListItem Value="1">2006</asp:ListItem>
                <asp:ListItem Value="2">2007</asp:ListItem>
                <asp:ListItem Value="3">2008</asp:ListItem>
                <asp:ListItem Value="4">2009</asp:ListItem>
            </asp:DropDownList>
        </td>
    </tr>
    <tr>
        <td class="RowHeight" width="20%">
            Percentage</td>
        <td colspan="3">
            <asp:TextBox ID="percentageBox" runat="server"></asp:TextBox>
        </td>
    </tr>
    <tr>
        <td class="RowHeight" width="20%">
            Instutitute Name</td>
        <td colspan="3">
            <asp:TextBox ID="InstiNameBox" runat="server" Width="350px"></asp:TextBox>
        </td>
    </tr>
</table>

and that of aspx.cs page is as below.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Collections;

public partial class AppplicationForm2 : System.Web.UI.Page
{
    Control qualificationControl;
    UserControl usrqualificationControl = new UserControl();
    int CtrlID = 0;
    protected void Page_Load(object sender, EventArgs e)
    {
        qualificationControl = usrqualificationControl.LoadControl("~/control/qualificationControl.ascx");
        if (!IsPostBack)
        {
            ArrayList CtrlList = new ArrayList();
            qualificationControl.ID = CtrlID.ToString();
            UserCtrlHolder.Controls.Add(qualificationControl);
            CtrlList.Add(qualificationControl);
            Session.Add("qualiControl", CtrlList);
        }
        //else 
    }
    protected void addQualificationBtn_Click(object sender, EventArgs e)
    {
        ArrayList CtrlList = null;
        ArrayList CourseList = new ArrayList();
        ArrayList YearList = new ArrayList();
        ArrayList percentageList = new ArrayList();
        ArrayList InstituteList = new ArrayList();
        if (Session["qualiControl"] != null)
        {
            CtrlList = (ArrayList)Session["qualicontrol"];
        }
        qualificationControl.ID = CtrlList.Count.ToString();
        CtrlList.Add(qualificationControl);
        for (int i = 0; i < CtrlList.Count; i++)
        {
            UserCtrlHolder.Controls.Add((Control)CtrlList[i]);
        }
    }
    private void RestoreUserControl(ArrayList CourseList,ArrayList YearList,ArrayList PercentageList,ArrayList InstiNameList,ArrayList CtrlList)
    {
        for (int CtrlCnt = 0; CtrlCnt < CtrlList.Count - 1; CtrlCnt++)
        {
            Control userControl = (Control)UserCtrlHolder.FindControl(CtrlID.ToString());
            DropDownList dlCourseList = (DropDownList)userControl.FindControl("courseList");
            DropDownList dlYearList = (DropDownList)userControl.FindControl("yearList");
            TextBox percentageBox = (TextBox)userControl.FindControl("percentageBox");
            TextBox InstiNameBox = (TextBox)userControl.FindControl("InstiNameBox");

            dlCourseList.ClearSelection();
            dlYearList.ClearSelection();
            dlCourseList.Items.FindByText(CourseList[CtrlCnt].ToString()).Selected = true;
            dlYearList.Items.FindByText(CourseList[CtrlCnt].ToString()).Selected = true;
            percentageBox.Text = PercentageList[CtrlCnt].ToString();
            InstiNameBox.Text = PercentageList[CtrlCnt].ToString();
        }
    }

}

Robert Koritnik Robert Koritnik · Accepted Answer · 2011-04-14T12:33:00

Use `Page_Init`

Using Page_Load event for dynamic user control loading is too late because view state has already been loaded. Hence your controls are always rendered empty. Try adding your user control in Page_Init event instead. View state gets loaded just after this event which makes sure your dynamic controls should⁺⁺⁺ be populated with previous state.

Note +++: If you add dynamic controls deterministically everything will be fine, but if you have non-deterministic processing your controls will have different IDs during page life hence view state will fail to load on each postback. You shouldn't have any problems with code you've provided.

Problem loading states of server controls residing in user control

2 Answers

Use Page_Init

Use `Page_Init`