Error while using "State Bags".

[Guest]

Hi:

The following ASP.NET code segment throws an "Object reference not set to an
instance of an object" exception.
------------------
Public Sub Page_Load(Source As Object, E As EventArgs)

Dim viewCount As Integer

If ViewState("viewCount").ToString() = "" Then
viewCount = 1
Else
viewCount = CType(ViewState("viewCount"), Integer) + 1
End If
labelViews.Text = "Times page has been viewed: " & viewCount.ToString()

ViewState("viewCount") = viewCount

 

[Guest]

Hi,

Perhaps the Viewstate("viewCount") is null. Try this; (Syntax might be
different, I'm not very fluent in VB)


Public Sub Page_Load(Source As Object, E As EventArgs)

Dim viewCount As Integer

If ViewState("viewCount") = Nothing Then
viewCount = 1
Else
viewCount = CType(ViewState("viewCount"), Integer) + 1
End If
labelViews.Text = "Times page has been viewed: " & viewCount.ToString()
ViewState("viewCount") = viewCount


I would also recommend to put

ViewState("viewCount") = viewCount

in the PreRender event instead of Page_Load, since this is the last event
called before the page renders and which eventually will have the latest
value of viewCount.


Hope this helps,

Ethem Azun

 

[Guest]

Thanks! That did work. The value was null.

Hi,

Perhaps the Viewstate("viewCount") is null. Try this; (Syntax might be
different, I'm not very fluent in VB)


Public Sub Page_Load(Source As Object, E As EventArgs)

Dim viewCount As Integer

If ViewState("viewCount") = Nothing Then
viewCount = 1
Else
viewCount = CType(ViewState("viewCount"), Integer) + 1
End If
labelViews.Text = "Times page has been viewed: " & viewCount.ToString()
ViewState("viewCount") = viewCount


I would also recommend to put

ViewState("viewCount") = viewCount

in the PreRender event instead of Page_Load, since this is the last event
called before the page renders and which eventually will have the latest
value of viewCount.


Hope this helps,

Ethem Azun

 

[Guest]

By the way, ViewState is not the right place to have an application wide
view counter on the page. ViewState is only defined per connection on the
page level.

I would recommend keeping this information either on application level, or
on another persistent datasource like a database (especially if you have many
pages that you want to show this info about.)

Ethem

 

[Guest]

Thanks:

With this source code I was trying to understand State Bags. The actual
purpose was not to implement a page counter.

All that I did was to understand how a key could be added to the ViewState
Property collection such that the value is persisted along with all other
server controls on the page.