Originariamente inviato da papillon68
Prova ad abilitare EnableViewState nelle proprietà della DropDownList. Funziona ?
FUNZIONA con ViewState abilitato o no. Questa è la pagina completa di collaudo:

pagina
codice:
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="a.aspx.vb" Inherits="prove_a" %>

<!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">
    <div>
        <asp:Label ID="Label1" runat="server" EnableViewState="false" Text=""></asp:Label>
        <hr />
        <asp:Panel ID="Panel1" runat="server">
        </asp:Panel>
    </div>
    </form>
</body>
</html>
codice
codice:
Option Strict On
Imports l = libreria.ModuloWeb

Partial Class prove_a
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim ddlSottoCategoria As New DropDownList
        ddlSottoCategoria.Text = Nothing
        ddlSottoCategoria.ID = "txtBox" '& x.ToString
        ddlSottoCategoria.AutoPostBack = True
        Panel1.Controls.Add(ddlSottoCategoria)
        ddlSottoCategoria.Visible = True

        'If ddlSottoCategoria.Items.Count = 0 Then
        '    connetti(Session("database"))
        '    Sql = "SELECT * FROM ecommerce_categorie WHERE appartenenteCategoria = " & ddlCategoria.SelectedValue & " AND titoloCategoria <> 'Tutte'"
        '    objCmd = New SqlCommand(Sql, objConn)
        '    objDR = objCmd.ExecuteReader()

        '    Dim itm As New ListItem
        '    itm.Text = "Seleziona una categoria"
        '    itm.Value = 0
        '    ddlSottoCategoria.Items.Add(itm)
        '    Do While (objDR.Read())
        '        Dim itm2 As New ListItem
        '        itm2.Text = objDR("titoloCategoria").ToString()
        '        itm2.Value = objDR("idCategoria")
        '        ddlSottoCategoria.Items.Add(itm2)
        '    Loop
        'End If

        ddlSottoCategoria.EnableViewState = False
        AddHandler ddlSottoCategoria.SelectedIndexChanged, AddressOf ddlSottoCategoria_SelectedIndexChanged
        msole.FillListControl(ddlSottoCategoria, gl.StringaConnessioneRegioniProvinceComune, "regioni", "nome_regione", "id_regione", New ListItem("", ""))

    End Sub

    Protected Sub ddlSottoCategoria_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs)
        Dim d As DropDownList = DirectCast(sender, DropDownList)
        Me.Label1.Text = d.SelectedItem.Text
    End Sub
End Class