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Old April 26th, 2011, 03:26 PM
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Default Error - Object reference not set to an instance of an object

Hi Everyone

Wondered if anyone had come across 'Object reference not set to an instance of an object' before when working with sessions?

I am trying to pass values between pages in a web project I'm building. The first block of code below creates the session from a class instance.

Protected Sub LoanButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles LoanButton.Click

        Dim row As DetailsViewRow = ResourceDetailsView.Rows(1)
        Dim PublicationID As Integer = row.Cells(1).Text
        Dim rowOne As DetailsViewRow = ResourceDetailsView.Rows(2)
        Dim PublicationTitle As String = rowOne.Cells(1).Text

        Dim myPublication As New Publication

        myPublication.PublicationID = PublicationID
        myPublication.PublicationTitle = PublicationTitle
        System.Web.HttpContext.Current.Session("Publication") = myPublication

    End Sub
This block of code apprears as you can see on the page load event of the next page which is suppose to retrieve the variables I've stored in the session? I've used this procedure before in the past with help from Imar but for some reason on this occassion all i'm getting is 'Object reference not set to an instance of an object'?

Dim PubID As Integer
    Dim PubTitle As String
    Dim currentUser As String = Membership.GetUser().UserName

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

        Dim chosenPublication As Publication = System.Web.HttpContext.Current.Session("Publication")
        PubTitle = chosenPublication.GetPublicationTitle

        StatusMessage.Text = PubTitle

    End Sub

Does anyone have experience of this fault?


Old April 29th, 2011, 02:01 AM
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Which line of your Page_load event throws the exception?

I'm still learning all of this myself, but I see in the first code you used


and the second box you use


Did you define the property GetPublicationTitle?
Old April 30th, 2011, 05:18 AM
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Hi Phil,

Are you sure both code blocks get executed? Your code looks like it should work. What happens when you debug the application? Can you see what exactly s null / Nothing and where?

Also, inside a Page class there's no need to access the HttpContext. Using Session directly should work as well (as it's a property on the Page class):

Session("Publication") = myPublication

Imar Spaanjaars
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Author of Beginning ASP.NET 4.5 : in C# and VB, Beginning ASP.NET Web Pages with WebMatrix
and Beginning ASP.NET 4 : in C# and VB.
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