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Posted 18 Feb 2003

Retaining State for Dynamically Created Controls in ASP.NET applications

, 18 Feb 2003
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When creating controls on the fly on your ASP.NET pages viewstate is a bit hard to track. Learn how it works and how to help your application remembers where to put what.


When dynamically adding controls to an ASP.NET page in runtime the object references are lost at postback because they have no handle in the codebehind. The values entered by the user is not availible when accessing these objects after postback, and they seem empty. This article describes how to use ViewState to recreate and reinsert the postback values into the objects to access their values.


An ASP.NET application with pages that use dynamic generation of controls that need to retain state across postbacks. The solution described in this paper enables you to create a totally dynamic number of controls at runtime and retreive their values after postback.


Dynamically added controls have no object reference variable in the codebehind class. They appear only in the control collection of the containing control, i.e. the Page.Controls collection. When the page is posted back to the server as a result of user interaction a new instance of the codebehind class is instantiated, and all the variables of the class is set with values from the ViewState.

This means that the objects we are accessing from the codebehind class, that "feels" like the same objects as we worked on before postback, actually are new ones that got their predecessors values via ViewState and ASP.NET state management.

So, the controls that were dynamically created are no longer there and consequently the values returned from these controls have no place to go. They are lost in the viewstate.

In order to catch these values the dynamically generated controls needs to be re-generated at Page_Load. The important thing is to assign the same ID to each control. The ViewState uses the ID property of the Control objects to reinstate the values.

Add the following elements to your System.UI.Page class:

public class DynamicallyAddingControls : System.Web.UI.Page
    // a Property that manages a counter stored in ViewState
    protected int NumberOfControls
        get{return (int)ViewState["NumControls"];}
        set{ViewState["NumControls"] = value;}

    private void Page_Load(object sender, System.EventArgs e)
            //Initiate the counter of dynamically added controls
            this.NumberOfControls = 0;                
            //Controls must be repeatedly be created on postback

    // This routine creates the controls and assigns a generic ID
    private void createControls()
        int count = this.NumberOfControls;

        for(int i = 0; i < count; i++)
            TextBox tx = new TextBox();
            tx.ID = "ControlID_" + i.ToString();
            //Add the Controls to the container of your choice

    // example of dynamic addition of controls
    // note the use of the ViewState variable
    private void addSomeControl()
        TextBox tx = new TextBox();
        tx.ID = "ControlID_" + NumberOfControls.ToString();



Note that the createControls method has to simulate the way that you dynamically built your page before the postback. The important thing here is obviously to assign identical ID values to the correct type of controls to that we can access them at postback.

Points of Interest

This solution works because the ASP.NET ViewState supports dynamically added controls, but does not do the re-generation for us. As long as the ID properties match ASP.NET does the rest of the job for us.

Thanks to Eric Sütter for providing valuable input on this article!


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Mads Nissen
Software Developer (Senior)
Norway Norway

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Comments and Discussions

AnswerRe: Can't get value after postback Pin
saswata.purkayastha@gmail.com28-Dec-06 21:05
membersaswata.purkayastha@gmail.com28-Dec-06 21:05 
GeneralRe: Can't get value after postback Pin
DiskJunky2-Aug-07 0:43
memberDiskJunky2-Aug-07 0:43 
GeneralRe: Can't get value after postback Pin
jugomkd18-Apr-08 0:50
memberjugomkd18-Apr-08 0:50 
Questionhow to use find control in table??? Pin
embeded25-Dec-05 16:19
memberembeded25-Dec-05 16:19 
i'm making polling project,but i've problem when how to find dynamic control that i've made..

i use this to create dynamic control:

Protected WithEvents PilBox As System.Web.UI.WebControls.TextBox
Protected WithEvents Table1 As System.Web.UI.WebControls.Table
Protected WithEvents CreateOptionButton As System.Web.UI.WebControls.Button
Protected WithEvents SaveButton As System.Web.UI.WebControls.Button

Private Sub CreateOptionButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CreateOptionButton.Click

Dim temp As Integer
Dim i As Integer = PilBox.Text

For temp = 1 To i
Dim tb As New System.Web.UI.WebControls.TextBox
tb.ID = "pil" & temp

Dim mycell As New TableCell
Dim c As New TableCell
c.Controls.Add(New LiteralControl("Answers option " & temp & " : "))
Dim myrow As New TableRow
Next temp

End Sub

when i call it by click SaveButton :

Private Sub SaveButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SaveButton.Click
Dim temp As Integer
Dim i As Integer = PilBox.Text

For temp = 1 To i
Dim myexisttb As TextBox
myexisttb = Table1.FindControl("pil" & temp)
'save to database by calling myexisttb
Next temp
End Sub

when i click SaveButton, dynamic control that i made before disappear..
and there's error :
Object reference not set to an instance of an object.

Anybody can help me?? Thanks before..

Merry Christmast and Happy New Year 2006 to you all....

GeneralAcess Data for update, insert, ... Pin
Vitor Hugo Barros19-Jul-05 11:59
memberVitor Hugo Barros19-Jul-05 11:59 
GeneralRe: Acess Data for update, insert, ... Pin
smair30-Aug-05 23:16
membersmair30-Aug-05 23:16 
GeneralRe: Acess Data for update, insert, ... Pin
Vitor Hugo Barros31-Aug-05 5:39
memberVitor Hugo Barros31-Aug-05 5:39 
GeneralRe: Acess Data for update, insert, ... Pin
RB@Emphasys7-Sep-06 11:23
memberRB@Emphasys7-Sep-06 11:23 
Generalfind control of placeholder,pls help:-) Pin
Anonymous19-Jul-05 9:38
sussAnonymous19-Jul-05 9:38 
GeneralLabel problem Pin
biktor817-Jun-05 7:15
memberbiktor817-Jun-05 7:15 

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