Bernard,

Every time you build controls dynamically, you are responsible for
recreating them on postback. I suspect you way of thinking is once control
has been instantiated dynamically the entire control is kept in the
viewstate. I am right? Well, this is not true. Controls store only some of
the information required for rebuilding. If control has not been instantiated
on postback, it’s obvious if it does not exist it cannot restore its state
from viewstate. Hence, if you want to build DataList dynamically, handle
itemcreated event to instantiate the controls for every row. I prepared a
fully working example to show you how it should be done.

-- aspx page code --

<asp:DataList ID="dataList" runat="server" />
<asp:Button ID="btnSubmit" runat="server" Text="Submit" />

-- code beside / behind --

Imports System.Data
Imports System.Collections.Generic

Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub dataList_ItemDataBound( _
        ByVal sender As Object, _
        ByVal e As System.Web.UI.WebControls.DataListItemEventArgs) _
        Handles dataList.ItemDataBound

        With e.Item

            If .ItemType = ListItemType.Item Or _
              .ItemType = ListItemType.AlternatingItem Then

                Dim row As DataRow = CType(.DataItem, DataRowView).Row

                Dim label As Label = .FindControl(LabelId)
                label.Text = row("Name")

                Dim textBox As TextBox = .FindControl(TextBoxId)
                textBox.Text = row("Date")

            End If

        End With

    End Sub

    Protected Sub dataList_ItemCreated(_
        ByVal sender As Object, _
        ByVal e As System.Web.UI.WebControls.DataListItemEventArgs) _
        Handles dataList.ItemCreated

        With e.Item

            If .ItemType = ListItemType.Item Or _
            .ItemType = ListItemType.AlternatingItem Then

                ' label
                Dim label As New Label()

                label.ID = LabelId
                label.ForeColor = Drawing.Color.Blue

                .Controls.Add(label)

                ' text box
                Dim textBox As New TextBox

                textBox.ID = TextBoxId
                textBox.Width = New Unit(200)

                .Controls.Add(textBox)

            End If

        End With

    End Sub

    Protected Sub Page_Load( _
        ByVal sender As Object, _
        ByVal e As System.EventArgs) Handles Me.Load

        If Not IsPostBack Then

            dataList.DataSource = GetData()
            dataList.DataBind()

        End If

    End Sub

    Private Const TextBoxId As String = "txt"
    Private Const LabelId As String = "lbl"

    Private Function GetData() As DataTable

        Dim table As New DataTable()
        Dim row As DataRow

        table.Columns.Add("Id", GetType(Integer))
        table.Columns.Add("Name", GetType(String))
        table.Columns.Add("Date", GetType(DateTime))

        For i As Integer = 1 To 10

            row = table.NewRow()

            row(0) = i
            row(1) = "Name" + i.ToString()
            row(2) = DateTime.Now.AddMinutes(i)

            table.Rows.Add(row)

        Next

        Return table

    End Function

    Protected Sub btnSubmit_Click(_
        ByVal sender As Object, _
        ByVal e As System.EventArgs) _
        Handles btnSubmit.Click

        Dim dates As New List(Of DateTime)

        For Each item As DataListItem In dataList.Items

            Dim textBox As TextBox = item.FindControl(TextBoxId)
            dates.Add(DateTime.Parse(textBox.Text))

        Next

    End Sub

End Class

hope this helps