Session Variable-InvalidCastException

[Don Miller]

I use a Session variable to store a custom object (all properties contain
strings) between postbacks. On occasion, mostly when I change and save code,
when I refresh the web page to see the changes, I get an error:

"System.Invalid CastException was unhandled by user code -Unable to cast
object of type 'QueryParameter s' to type 'QueryParameter s'"

in the function below which is called during Page_Load (_queryParamete rs =
QueryParameters .getInstance())

Public Shared Function getInstance() As QueryParameters
Dim instance As QueryParameters
If IsNothing(Curre nt.Session(SESS ION_VARIABLE)) Then
instance = New QueryParameters ()
instance.saveQP ToSession()
Else
instance = Current.Session (SESSION_VARIAB LE)
End If
Return instance
End Function

When I debug, a valid Session variable exists because the code goes to the
Else statement, and in the Watch window, I can see all the properties of the
custom object in the Session variable. Since 'instance' is typed as
QueryParameters and a Session variable exists that holds the object, I don't
understand why there is an error since these both seem to be typed correctly
as QueryParameters . Even when I explicitly type the session variable
(CType(Current. Session(SESSION _VARIABLE), QueryParameters )) the same error
appears.

If I close the browser completely, everything works, but I hate to have to
close a browser with every iteration of code changes.

Does anyone know why this error appears? Thanks for any help.

[Laurent Bugnion, MVP]

Re: Session Variable-InvalidCastExce ption

Hi,

Don Miller wrote:

I use a Session variable to store a custom object (all properties contain
strings) between postbacks. On occasion, mostly when I change and save code,
when I refresh the web page to see the changes, I get an error:
>
"System.Invalid CastException was unhandled by user code -Unable to cast
object of type 'QueryParameter s' to type 'QueryParameter s'"

The symptoms make me think of that error:

http://weblogs.asp.net/scottgu/archive/2007/04/11/public-hotfix-patch-available-for-asp-net-compilation-issues.aspx

Could that be it?

Greetings,
Laurent

>
in the function below which is called during Page_Load (_queryParamete rs =
QueryParameters .getInstance())
>
Public Shared Function getInstance() As QueryParameters
Dim instance As QueryParameters
If IsNothing(Curre nt.Session(SESS ION_VARIABLE)) Then
instance = New QueryParameters ()
instance.saveQP ToSession()
Else
instance = Current.Session (SESSION_VARIAB LE)
End If
Return instance
End Function
>
When I debug, a valid Session variable exists because the code goes to the
Else statement, and in the Watch window, I can see all the properties of the
custom object in the Session variable. Since 'instance' is typed as
QueryParameters and a Session variable exists that holds the object, I don't
understand why there is an error since these both seem to be typed correctly
as QueryParameters . Even when I explicitly type the session variable
(CType(Current. Session(SESSION _VARIABLE), QueryParameters )) the same error
appears.
>
If I close the browser completely, everything works, but I hate to have to
close a browser with every iteration of code changes.
>
Does anyone know why this error appears? Thanks for any help.
>
>

--
Laurent Bugnion [MVP ASP.NET]
Software engineering, Blog: http://www.galasoft-LB.ch
PhotoAlbum: http://www.galasoft-LB.ch/pictures
Support children in Calcutta: http://www.calcutta-espoir.ch

[Don Miller]

Re: Session Variable-InvalidCastExce ption

>"System.Invali dCastException was unhandled by user code -Unable to cast

>object of type 'QueryParameter s' to type 'QueryParameter s'"

>
The symptoms make me think of that error:

http://weblogs.asp.net/scottgu/archive/2007/04/11/public-hotfix-patch-available-for-asp-net-compilation-issues.aspx

>
Could that be it?

I tried the simple workaround (changing the web config file system "batch"
to false) and the error message persisted (run the application, type in
garbage in the code-behind, erase the garbage, save the file, hit refresh in
the browser). I am leary of applying the hotfix. I may just end up putting
my properties into hidden fields instead of an object in a Session variable
and forgetting this bug.

Something to do with changing the source code file and compilation.