Saving provider state?

[dotnet_vb_newbie]

My design-time code produces "name ViewState is not defined". Am I
missing a definition or assignment in my provider code? The beginning
of the code follows:

Imports System.ComponentModel
Imports System.io
Imports System.Web.UI.WebControls
Imports System.Runtime.Serialization.Formatters.Soap
Imports System.Drawing.Design
Imports System.Text.RegularExpressions
Imports System.Runtime.Serialization
Imports System.Web.UI.StateBag
Imports System.Web
Imports System.Web.UI

<Serializable(), DesignTimeVisible(), _
ProvideProperty("RequiredField", GetType(WebControl)), _
ProvideProperty("ErrorColor", GetType(WebControl)), _
ProvideProperty("RegularExpression", GetType(WebControl))> _

Public Class TextBoxValidator

Inherits System.ComponentModel.Component
Implements IExtenderProvider