Public Sub New()
        InitializeComponent()

        Dim table As New DataTable
        table.Columns.Add("Id", GetType(Integer))
        table.Columns.Add("Name")
        For index = 1 To 10
            table.Rows.Add(index, "Name " & index)
        Next

        RadDropDownList1.DataSource = table
        RadDropDownList1.DisplayMember = "Name"
        RadDropDownList1.ValueMember = "Id"

    End Sub

    Private Sub RadButton1_Click(sender As System.Object, e As System.EventArgs) Handles RadButton1.Click
        Dim item As New RadListDataItem()
        item.Text = "hello"
        item.Value = 123
        RadDropDownList1.Items.Add(item) 'here the item does not have a valid value

    End Sub