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Asked: 2026-05-11T10:58:53+00:00

I have a page that contains some dynamically created controls (TextBox and DropDownList). When

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I have a page that contains some dynamically created controls (TextBox and DropDownList). When a postback occurs, the TextBoxes keep their values, but the DropDownLists lose their ListItems. This is quite confusing, since the page level DropDownList also keeps its ListItems. Can anyone see what’s wrong with the code below?

Any help in solving this issue would be greatly appreciated.

<%@ Page Language='VB'%>  <script runat='server'>   Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs)     If Not Page.IsPostBack Then       ddlFixed.Items.Add(New ListItem('12', '13'))       ddlFixed.Items.Add(New ListItem('14', '15'))     End If     Dim i As Integer     For i = 0 To 3       Dim ddl As New DropDownList       ddl.ID = 'ddlPage' & i       ddl.EnableViewState = True       If Not Page.IsPostBack Then         ddl.Items.Add(New ListItem('12', '13'))         ddl.Items.Add(New ListItem('14', '15'))       End If       pnlDynamic.Controls.Add(ddl)       Dim txtBx As New TextBox       txtBx.ID = 'txtPage' & i       If Not Page.IsPostBack Then         txtBx.Text = 'Preset'       End If       pnlDynamic.Controls.Add(txtBx)     Next   End Sub </script>   <html xmlns='http://www.w3.org/1999/xhtml'> <head runat='server'>   <title></title> </head> <body>   <form id='form1' runat='server' enableviewstate='true'>   <div>     <br />     <br />     <a href='Default.aspx'>Get-Request</a>     <br />     <br />     <asp:Panel runat='server' ID='pnlDynamic' EnableViewState='true' />         <br />     <br />     <asp:DropDownList runat='server' ID='ddlFixed' />     <asp:Button runat='server' ID='btn' Text='Postback'/>   </div>   </form> </body> </html>
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1 Answer

  1. I have found the solution that will allow me to keep the viewstate across postbacks. It’s to call TrackViewState of the ItemCollection.

    CType(ddl.Items, IStateManager).TrackViewState()

    Thanks to all for your help.

    This is the working solution:

    <%@ Page Language='VB'%>  <script runat='server'>   Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs)     If Not Page.IsPostBack Then       ddlFixed.Items.Add(New ListItem('12', '13'))       ddlFixed.Items.Add(New ListItem('14', '15'))     End If     Dim i As Integer     For i = 0 To 3       Dim ddl As New DropDownList       ddl.ID = 'ddlPage' & i       CType(ddl.Items, IStateManager).TrackViewState()       If Not Page.IsPostBack Then         ddl.Items.Add(New ListItem('12', '13'))         ddl.Items.Add(New ListItem('14', '15'))       End If       pnlDynamic.Controls.Add(ddl)       Dim txtBx As New TextBox       txtBx.ID = 'txtPage' & i       If Not Page.IsPostBack Then         txtBx.Text = 'Preset'       End If       pnlDynamic.Controls.Add(txtBx)     Next   End Sub </script>   <html xmlns='http://www.w3.org/1999/xhtml'> <head id='Head1' runat='server'>   <title></title> </head> <body>   <form id='form1' runat='server' >   <div>     <br />     <br />     <a href='Default.aspx'>Get-Request</a>     <br />     <br />     <asp:Panel runat='server' ID='pnlDynamic' />         <br />     <br />     <asp:DropDownList runat='server' ID='ddlFixed' />     <asp:Button runat='server' ID='btn' Text='Postback'/>   </div>   </form> </body> </html>
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