UserControl values lost on PostBack

30 Aug 2006 1:43 AM

paul.hester

Hi all,

I have a very simple user control that contains 3 drop downs. Whenever
there's a postback the values of these drop downs are lost. I've tried
enabling viewstate everywhere without success. Could anyone shed any
light on what's going wrong?

Thanks,

Paul

Asx:

<%@ Control Language="C#" EnableViewState="true" AutoEventWireup="true"
CodeFile="DayMonthYear.ascx.cs" Inherits="Test.DayMonthYear" %>
<%@ Register TagPrefix="test" Namespace="Test" %>
<table cellpadding="1" cellspacing="0">
    <tr>
        <td><small>Day</small></td>
        <td><small>Month</small></td>
        <td><small>Year</small></td>
    </tr>
    <tr>
        <td><asp:DropDownList ID="day" EnableViewState="true"
runat="server"></asp:DropDownList></td>
        <td><asp:DropDownList ID="month" EnableViewState="true"
runat="server"></asp:DropDownList></td>
        <td><asp:DropDownList ID="year" EnableViewState="true"
runat="server"></asp:DropDownList></td>
    </tr>
</table>

Asx.Cs:

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

namespace Test
{
    public partial class DayMonthYear : System.Web.UI.UserControl,
INamingContainer
    {
        private int _yearHigh = DateTime.Now.Year;
        private int _yearLow = DateTime.Now.Year - 100;

        protected void Page_PreRender(object sender, EventArgs e)
        {
            string[] months = new string[] { "January", "February", "March",
"April", "May", "June", "July", "August", "September", "October",
"November", "December" };

            // add days
            day.Items.Add(new ListItem(string.Empty, "0"));
            for (int i = 1; i < 32; i++)
                day.Items.Add(i.ToString());

            // add months
            month.Items.Add(new ListItem(string.Empty, "0"));
            for (int i = 0; i < months.Length; i++)
                month.Items.Add(new ListItem(months[i], (i + 1) + string.Empty));

            // add years
            year.Items.Add(new ListItem(string.Empty, "0"));
            for (int i = YearLow; i <= YearHigh; i++)
                year.Items.Add(i.ToString());
        }

        public int YearHigh
        {
            get { return _yearHigh; }
            set { _yearHigh = value; }
        }

        public int YearLow
        {
            get { return _yearLow; }
            set { _yearLow = value; }
        }
    }
}

31 Aug 2006 8:41 AM

offwhite@gmail.com

In a User Control you will lose the PostBack value if you cause data
binding to happen before you can get the values.

You may want to use code like this...

if (!Page.IsPostBack) {
... bind month controls ...
}

In your case I see the binding is done manually on PreRender. For
starters that is a curious place to put the binding. Normally you want
it done in the Load event handler.

Look at the page life cycle and see where it loads the ViewState and
where the other events are handled in the life cycle.

http://msdn2.microsoft.com/en-us/library/ms178472.aspx

Brennan Stehling
http://brennan.offwhite.net/blog/

paul.hes***@gmail.com wrote:
Show quoteHide quote

> Hi all,
>
> I have a very simple user control that contains 3 drop downs. Whenever
> there's a postback the values of these drop downs are lost. I've tried
> enabling viewstate everywhere without success. Could anyone shed any
> light on what's going wrong?
>
> Thanks,
>
> Paul
>
> Asx:
>
> <%@ Control Language="C#" EnableViewState="true" AutoEventWireup="true"
> CodeFile="DayMonthYear.ascx.cs" Inherits="Test.DayMonthYear" %>
> <%@ Register TagPrefix="test" Namespace="Test" %>
> <table cellpadding="1" cellspacing="0">
>     <tr>
>         <td><small>Day</small></td>
>         <td><small>Month</small></td>
>         <td><small>Year</small></td>
>     </tr>
>     <tr>
>         <td><asp:DropDownList ID="day" EnableViewState="true"
> runat="server"></asp:DropDownList></td>
>         <td><asp:DropDownList ID="month" EnableViewState="true"
> runat="server"></asp:DropDownList></td>
>         <td><asp:DropDownList ID="year" EnableViewState="true"
> runat="server"></asp:DropDownList></td>
>     </tr>
> </table>
>
> Asx.Cs:
>
> using System;
> using System.Data;
> using System.Configuration;
> using System.Collections;
> using System.Web;
> using System.Web.Security;
> using System.Web.UI;
> using System.Web.UI.WebControls;
> using System.Web.UI.WebControls.WebParts;
> using System.Web.UI.HtmlControls;
>
> namespace Test
> {
>     public partial class DayMonthYear : System.Web.UI.UserControl,
> INamingContainer
>     {
>         private int _yearHigh = DateTime.Now.Year;
>         private int _yearLow = DateTime.Now.Year - 100;
>
>         protected void Page_PreRender(object sender, EventArgs e)
>         {
>             string[] months = new string[] { "January", "February", "March",
> "April", "May", "June", "July", "August", "September", "October",
> "November", "December" };
>
>             // add days
>             day.Items.Add(new ListItem(string.Empty, "0"));
>             for (int i = 1; i < 32; i++)
>                 day.Items.Add(i.ToString());
>
>             // add months
>             month.Items.Add(new ListItem(string.Empty, "0"));
>             for (int i = 0; i < months.Length; i++)
>                 month.Items.Add(new ListItem(months[i], (i + 1) + string.Empty));
>
>             // add years
>             year.Items.Add(new ListItem(string.Empty, "0"));
>             for (int i = YearLow; i <= YearHigh; i++)
>                 year.Items.Add(i.ToString());
>         }
>
>         public int YearHigh
>         {
>             get { return _yearHigh; }
>             set { _yearHigh = value; }
>         }
>
>         public int YearLow
>         {
>             get { return _yearLow; }
>             set { _yearLow = value; }
>         }
>     }
> }