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SelectedValue lost on postback in dynamically added user controls

14 Answers 928 Views

ComboBox

This is a migrated thread and some comments may be shown as answers.

Richard asked on 29 Jun 2012, 10:20 AM

We recently upgraded to the lates version of Telerik Ajax Controls (from 2010 Q2), and have an issue with the ComboBox.

We are dynaimcally loading user controls that contains comboboxes with autopostback set to true.
The problem is that the comboboxes selected values are lost on postback.

This works well when we use the old dll (2010 Q2).

I have tried the dll from Q3 2011 and i have the same problem with that.
Do you have any idea what would cause this?

Regards, Richard

Here is the code for the aspx:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="Modules_DEV_ComboboxBug_Default" %>

<%@ Register src="WebUserControl.ascx" tagname="WebUserControl" tagprefix="uc" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<head runat="server">

<title></title>

</head>

<body>

<form id="form1" runat="server">

<telerik:RadScriptManager runat="server" ID="rsm"></telerik:RadScriptManager>

<div>

<asp:PlaceHolder runat="server" ID="phContent" />

</div>

</form>

</body>

</html>

aspx.cs:

using System;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using Telerik.Web.UI;

public partial class Modules_DEV_ComboboxBug_Default : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

WebUserControl uc = (WebUserControl)Page.LoadControl("WebUserControl.ascx");

uc.ID = "WebUserControl";

phContent.Controls.Add(uc);

}

ascx:

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="WebUserControl.ascx.cs" Inherits="WebUserControl" %>

<telerik:radComboBox runat="server" ID="RadComboBox1" AutoPostBack="true">

</telerik:radComboBox>

<telerik:radComboBox runat="server" ID="RadComboBox2" AutoPostBack="true">

</telerik:radComboBox>

ascx.cs:

using System;

using System.Collections;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

public partial class WebUserControl : System.Web.UI.UserControl

{

protected void Page_Load(object sender, EventArgs e)

{

string[] dataSource = new string[] {"UnSelected", "First", "Second", "Third" };

RadComboBox1.DataSource = dataSource;

RadComboBox1.DataBind();

RadComboBox2.DataSource = dataSource;

RadComboBox2.DataBind();

}

14 Answers, 1 is accepted

answered on 02 Jul 2012, 11:24 AM

Hello Richard,

RadComboBox performs a Post Back every time a different item is selected and this causes a new page load. When the Load stage of the page life cycle is reached the RadComboBox is rebound, and this action overwrites the previous selected values. You could consider using 2 approaches in order to resolve this issue. The first one is to bind the control only upon initial load as shown below:

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

public partial class WebUserControl : System.Web.UI.UserControl

{

protected void Page_Load(object sender, EventArgs e)

{

string[] dataSource = new string[] { "UnSelected", "First", "Second", "Third" };

if (!Page.IsPostBack)

{

RadComboBox1.DataSource = dataSource;

RadComboBox1.DataBind();

RadComboBox2.DataSource = dataSource;

RadComboBox2.DataBind();

}

The second approach is to perform data binding at the Init stage of the life cycle, because at that point the ViewState is still not applied.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using Telerik.Web.UI;

public partial class WebUserControl : System.Web.UI.UserControl

{

protected void Page_Init(object sender, EventArgs e)

{

string[] dataSource = new string[] { "UnSelected", "First", "Second", "Third" };

RadComboBox1.DataSource = dataSource;

RadComboBox1.DataBind();

RadComboBox2.DataSource = dataSource;

RadComboBox2.DataBind();

}

protected void Page_Load(object sender, EventArgs e)

{

}

Regards,
Nencho
the Telerik team

If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed now.

answered on 01 Aug 2012, 02:51 PM

Hi Richard,

There have been a lot of bug fixes, improvements and new features added for the passed two years which might has caused a change in the behavior of the controls.

A simple solution of your problem would be to cache the selection before binding the control and applied it afterwards. Here is a sample implementation:

protected void Page_Load(object sender, EventArgs e)

{

var cachedSelectionFirstComboBox = RadComboBox1.SelectedValue;

var cachedSelectionSecondComboBox = RadComboBox2.SelectedValue;

string[] dataSource = new string[] { "UnSelected", "First", "Second", "Third" };

RadComboBox1.DataSource = dataSource;

RadComboBox1.DataBind();

RadComboBox2.DataSource = dataSource;

RadComboBox2.DataBind();

RadComboBox1.SelectedValue = cachedSelectionFirstComboBox;

RadComboBox2.SelectedValue = cachedSelectionSecondComboBox;

}

All the best,
Dimitar Terziev
the Telerik team

answered on 30 Oct 2012, 11:41 AM

Hello Justin,

In general the selected value will be persisted when the control is being bound to the data source only once. When binding is performed the previous selection is cleared since you might be filling different data and therefore it is not valid to keep selection for something which might not be in the current data set. Since in this particular scenario the control is being bound upon every post back, this caching is necessary because the selection is cleared after the binding is performed. In case the binding is performed in Page_Init event thus the selection will be persisted since the ViewState is not applied yet.

Greetings,
Dimitar Terziev
the Telerik team

answered on 22 Apr 2015, 07:15 AM

sample.zip

Hi,

I have prepared a sample page implementing a similar scenario to the describe one using the 2014.3.1209 version of our controls and the selection of the RadComboBox is correctly preserved across postbacks. You could find the sample attached.

Regards,
Dimitar Terziev
Telerik

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SelectedValue lost on postback in dynamically added user controls

14 Answers, 1 is accepted