Manage ViewState Using ASP.NET 2.0 Provider Architecture

Imports System.IO
Imports System.Web.UI
Imports System.Collections.Specialized
Imports System.Text


Namespace System.Web.Configuration.Providers

	''' <summary>
	'''	ViewState Provider that compresses the view state string and stores it in page's hidden variable. 
	''' </summary>
	''' <remarks>
	''' Scott Galloway has a blog entry where he discusses his experiences with using #ziplib library to compress the view state. 
	''' For more info, please visit http://www.mostlylucid.co.uk/ 
	''' Inspiration from implementation in http://www.codeproject.com/aspnet/ViewStateProvider.asp 
	''' Based on code in http://msdn2.microsoft.com/en-us/library/aa479028.aspx
	''' </remarks>
	''' <history>
	''' 	[Oleg Sobol]	9/26/2006	Created
	''' </history>
	''' -----------------------------------------------------------------------------
	Public Class CompressionViewStateProvider
		Inherits ViewStateProvider


		Private _applicationName As String
		Private _los As New LosFormatter
		Private _lockLoad As New Object
		Private _lockSave As New Object
		Private _viewStateKeyName As String = "__COMPRESSEDVIEWSTATE"

#Region " Properties "

		Public Overrides Property ApplicationName() As String
			Get
				Return _applicationName
			End Get
			Set(ByVal value As String)
				_applicationName = value
			End Set
		End Property

		Public Overrides Property ViewStateKeyName() As String
			Get
				Return _viewStateKeyName
			End Get
			Set(ByVal value As String)
				_viewStateKeyName = value
			End Set
		End Property
#End Region


		Public Overloads Overrides Sub Initialize(ByVal name As String, ByVal config As NameValueCollection)
			' Verify that config isn't null
			If config Is Nothing Then Throw New ArgumentNullException("config")
			' Assign the provider a default name if it doesn't have one
			If String.IsNullOrEmpty(name) Then name = "CompressionViewStateProvider"
			' Add a default "description" attribute to config if the attribute doesn�t exist or is empty
			If String.IsNullOrEmpty(config("description")) Then
				config.Remove("description")
				config.Add("description", "Compression viewstate provider")
			End If
			' Call the base class's Initialize method
			MyBase.Initialize(name, config)

			' Initialize _applicationName
			_applicationName = config("applicationName")
			If String.IsNullOrEmpty(_applicationName) Then _applicationName = "/"
			config.Remove("applicationName")


			' Throw an exception if unrecognized attributes remain
			If config.Count > 0 Then
				Dim attr As String = config.GetKey(0)
				If Not String.IsNullOrEmpty(attr) Then Throw New ViewStateProviderException("Unrecognized attribute: " + attr)
			End If
		End Sub


#Region " ViewStateProvider specific behaviors "
		Public Overloads Overrides Function LoadPageState(ByVal pControl As Control) As Object
			SyncLock _lockLoad
				Dim vsString As String = CType(pControl, Page).Request.Form(_viewStateKeyName)
				Dim outStr As String = Util.Compression.DeCompress(vsString)
				Return _los.Deserialize(outStr)
			End SyncLock
		End Function

		Public Overloads Overrides Sub SavePageState(ByVal pControl As Control, ByVal viewState As Object)
			SyncLock _lockSave
				Dim writer As New StringWriter
				_los.Serialize(writer, viewState)
				Dim outStr As String = Util.Compression.Compress(writer.ToString)
				CType(pControl, Page).ClientScript.RegisterHiddenField(_viewStateKeyName, outStr)
				writer.Dispose()
			End SyncLock
		End Sub
#End Region

	End Class



End Namespace