VB.Net Initialising a class using System.Reflection and System.Type to create a session based singleton extension method - asp.net

Question

I have had several occasions recently to access a specific class several times over a relatively small time frame.
So I've been storing the value of the class in Session and trying to access it on page load, if it's not available creating a new instance and storing that in session.
So instead of constantly replicating the same code for different classes on different pages I'm trying to create an extension method to do this for me.
I want to use it like this
Dim objName as MyClass
objName.SessionSingleton()
So far this is what I have for my extension method:
<Extension()> _
Public Sub SessionSingleton(ByRef ClassObject As Object)
Dim objType As Type = ClassObject.GetType
Dim sessionName As String = objType.FullName
If TypeOf HttpContext.Current.Session(sessionName) Is objType And HttpContext.Current.Session(sessionName) <> "" Then
ClassObject = HttpContext.Current.Session(sessionName)
Else
Dim singleton As Object = New objType???????
HttpContext.Current.Session(sessionName) = singleton
ClassObject = singleton
End If
End Sub
I'm stuck on what to do when I make my new instance of my class (it would have to have a New() sub)
I'm not sure where to go from here... or even if this is the best way to do it.

Answer 1

I figured it out and am posting my code for reference. While digging thru pages about Class/Object Factories (thanks RBarry) I found several references to Activator.CreateInstance() in the System.Reflection Class I came up with this.
Imports Microsoft.VisualBasic
Imports System.Runtime.CompilerServices
Imports System.Reflection
Public Module enviornmentUtilities
<Extension()> _
Public Function SessionSinglton(ByVal objType As Type) As Object
Dim sessionName As String = objType.FullName.ToString
If Not HttpContext.Current.Session(sessionName) Is Nothing Then
HttpContext.Current.Trace.Write(HttpContext.Current.Session(sessionName).ToString)
Return HttpContext.Current.Session(sessionName)
Else
Dim ss = Activator.CreateInstance(objType)
HttpContext.Current.Session(sessionName) = ss
Return ss
End If
End Function
End Module
This will let you create a session based singleton from any class that does not require parameters in the new method (which isn't required for this to work)
To test I made a simple Class:
Public Class HasNew
Public FreshInstance As Boolean = True
Public Sub New()
HttpContext.Current.Trace.Warn("This Class has a new method")
End Sub
Public Sub CheckFreshness()
If FreshInstance Then
HttpContext.Current.Trace.Warn("Fresh HasNew Instance")
FreshInstance = False
Else
HttpContext.Current.Trace.Warn("NotFresh HasNew Instance")
End If
End Sub
Public Shared Function type() As Type
Return GetType(HasNew)
End Function
Public Shared Function SessionSinglton() As HasNew
Return GetType(HasNew).SessionSinglton
End Function
End Class
You'll notice the two Public Shared Methods type() and SessionSinglton which calls the above extension method.
With those two functions added we have three ways to initiate the Session Singlton demonstrated here:
Dim HN As HasNew
HN = HasNew.SessionSinglton
HN.CheckFreshness()
HN = HasNew.type.SessionSinglton
HN.CheckFreshness()
HN = GetType(HasNew).SessionSinglton
HN.CheckFreshness()
The Trace Output for this file is as follows:
This Class has a new method
Fresh HasNew Instance
NotFresh HasNew Instance
NotFresh HasNew Instance
The classes new() method is accessed on the first call to the SessionSinglton method and subsequent calls reflect that the instance is in fact being pulled from memory.
I hope this helps someone else in the future.

Answer 2

If you used generics you could just do New T(). Also your SessionSingleton returns "object" type, requiring casting. I did not test this but it should work.
Imports Microsoft.VisualBasic
Imports System.Runtime.CompilerServices
Imports System.Reflection
Public Module enviornmentUtilities
<Extension()> _
Public Function SessionSinglton(Of T As {Class, New})(ByVal obj As T) As T
Dim sessionName As String = obj.GetType.Name
If Not HttpContext.Current.Session(sessionName) Is Nothing Then
HttpContext.Current.Trace.Write(HttpContext.Current.Session(sessionName).ToString)
Return HttpContext.Current.Session(sessionName)
Else
Dim ss = New T()
HttpContext.Current.Session(sessionName) = ss
Return ss
End If
End Function
End Module