Trouble with using Session state

I'm having difficulty understanding Session state in ASP.Net. It's almost
embarrassing asking this as I've been using ASP since it was first released
& it really shouldn't be this hard to use - perhaps I'm just not very smart
or perhaps MS is making this too hard for us sql bunnies to understand - I
dunno, but I'd really appreciate someone explaining what I'm doing wrong
here & perhaps suggest a better approach..

I'm familiar with use of the old Session("variable") = value syntax. (also
very aware of scalability issues - so don't flame me on this - I'm just
trying to understand how the whole thing fits together here). I expected
things to work similarly with ASP.Net but I just can't get it to work easily
for me..

I'm trying to carry around a Session("login_id") type variable & would like
to access it via code-behind (.aspx.vb) modules as well as class (.vb)
modules. I can successfully set a variable in a Page_Load event from one
form (during postback) but after re-directing to another form, I get a nasty
error when trying to access the value:

Object reference not set to an instance of an object
Line 29: Dim LoginID As String
Line 30: LoginID = Session("LoginID").ToString

Source File: ... home.aspx.vb Line: 30

I've tried using HttpContext.Current.Session("LoginID").ToString but this
just gets the same problem.

Why do I get an Object reference not set error? Surely Session doesn't need
to be instanced does it?

I'd appreciate any help.

Regards,
Greg Linwood
SQL Server MVPwhen you transfer to another page, it isn't gauranteed to occur on the same
calling thread so all your state information, including session is discarded
and a new session built up to service the transfer call. If you want to
return state, there is an overloaded function parameter which enables you to
do so. Server.Transfer(page, bPreserveForm) set this to true and you will be
alright. the default is false. Same deal for redirect.

regards

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"Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote in
message news:OcFr9EMsDHA.1884@.TK2MSFTNGP10.phx.gbl...
> I'm having difficulty understanding Session state in ASP.Net. It's almost
> embarrassing asking this as I've been using ASP since it was first
released
> & it really shouldn't be this hard to use - perhaps I'm just not very
smart
> or perhaps MS is making this too hard for us sql bunnies to understand - I
> dunno, but I'd really appreciate someone explaining what I'm doing wrong
> here & perhaps suggest a better approach..
> I'm familiar with use of the old Session("variable") = value syntax. (also
> very aware of scalability issues - so don't flame me on this - I'm just
> trying to understand how the whole thing fits together here). I expected
> things to work similarly with ASP.Net but I just can't get it to work
easily
> for me..
> I'm trying to carry around a Session("login_id") type variable & would
like
> to access it via code-behind (.aspx.vb) modules as well as class (.vb)
> modules. I can successfully set a variable in a Page_Load event from one
> form (during postback) but after re-directing to another form, I get a
nasty
> error when trying to access the value:
> Object reference not set to an instance of an object
> Line 29: Dim LoginID As String
> Line 30: LoginID = Session("LoginID").ToString
> Source File: ... home.aspx.vb Line: 30
> I've tried using HttpContext.Current.Session("LoginID").ToString but this
> just gets the same problem.
> Why do I get an Object reference not set error? Surely Session doesn't
need
> to be instanced does it?
> I'd appreciate any help.
> Regards,
> Greg Linwood
> SQL Server MVP
Thanks Alvin - but that didn't work.

I changed my Response.Redirect to a Server.Transfer(page, True) and I still
get the same error...

I noticed that the bPreserveForm argument seems only to apply to QueryString
& Form state. I want to preserve variable values in Session state, similarly
to the manner in which ASP Session worked. Is this possible in ASP.Net?
Perhaps there's simply some setting I'm not getting right or something..

Regards,
Greg Linwood
SQL Server MVP

"Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com> wrote in
message news:ePvc9KMsDHA.2304@.tk2msftngp13.phx.gbl...
> when you transfer to another page, it isn't gauranteed to occur on the
same
> calling thread so all your state information, including session is
discarded
> and a new session built up to service the transfer call. If you want to
> return state, there is an overloaded function parameter which enables you
to
> do so. Server.Transfer(page, bPreserveForm) set this to true and you will
be
> alright. the default is false. Same deal for redirect.
> regards
> --
>
> ----
> Got TidBits?
> Get it here: www.networkip.net/tidbits
> "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote in
> message news:OcFr9EMsDHA.1884@.TK2MSFTNGP10.phx.gbl...
> > I'm having difficulty understanding Session state in ASP.Net. It's
almost
> > embarrassing asking this as I've been using ASP since it was first
> released
> > & it really shouldn't be this hard to use - perhaps I'm just not very
> smart
> > or perhaps MS is making this too hard for us sql bunnies to understand -
I
> > dunno, but I'd really appreciate someone explaining what I'm doing wrong
> > here & perhaps suggest a better approach..
> > I'm familiar with use of the old Session("variable") = value syntax.
(also
> > very aware of scalability issues - so don't flame me on this - I'm just
> > trying to understand how the whole thing fits together here). I expected
> > things to work similarly with ASP.Net but I just can't get it to work
> easily
> > for me..
> > I'm trying to carry around a Session("login_id") type variable & would
> like
> > to access it via code-behind (.aspx.vb) modules as well as class (.vb)
> > modules. I can successfully set a variable in a Page_Load event from one
> > form (during postback) but after re-directing to another form, I get a
> nasty
> > error when trying to access the value:
> > Object reference not set to an instance of an object
> > Line 29: Dim LoginID As String
> > Line 30: LoginID = Session("LoginID").ToString
> > Source File: ... home.aspx.vb Line: 30
> > I've tried using HttpContext.Current.Session("LoginID").ToString but
this
> > just gets the same problem.
> > Why do I get an Object reference not set error? Surely Session doesn't
> need
> > to be instanced does it?
> > I'd appreciate any help.
> > Regards,
> > Greg Linwood
> > SQL Server MVP
Try server.transfer(page.aspx, true).
Are you transferring to a page hosted in the application directory? That
should work otherwise the problem lies elsewhere.

regards

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"Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote in
message news:efMJYVMsDHA.640@.tk2msftngp13.phx.gbl...
> Thanks Alvin - but that didn't work.
> I changed my Response.Redirect to a Server.Transfer(page, True) and I
still
> get the same error...
> I noticed that the bPreserveForm argument seems only to apply to
QueryString
> & Form state. I want to preserve variable values in Session state,
similarly
> to the manner in which ASP Session worked. Is this possible in ASP.Net?
> Perhaps there's simply some setting I'm not getting right or something..
> Regards,
> Greg Linwood
> SQL Server MVP
> "Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com> wrote in
> message news:ePvc9KMsDHA.2304@.tk2msftngp13.phx.gbl...
> > when you transfer to another page, it isn't gauranteed to occur on the
> same
> > calling thread so all your state information, including session is
> discarded
> > and a new session built up to service the transfer call. If you want to
> > return state, there is an overloaded function parameter which enables
you
> to
> > do so. Server.Transfer(page, bPreserveForm) set this to true and you
will
> be
> > alright. the default is false. Same deal for redirect.
> > regards
> > --
> > ----
> > Got TidBits?
> > Get it here: www.networkip.net/tidbits
> > "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote
in
> > message news:OcFr9EMsDHA.1884@.TK2MSFTNGP10.phx.gbl...
> > > I'm having difficulty understanding Session state in ASP.Net. It's
> almost
> > > embarrassing asking this as I've been using ASP since it was first
> > released
> > > & it really shouldn't be this hard to use - perhaps I'm just not very
> > smart
> > > or perhaps MS is making this too hard for us sql bunnies to
understand -
> I
> > > dunno, but I'd really appreciate someone explaining what I'm doing
wrong
> > > here & perhaps suggest a better approach..
> > > > I'm familiar with use of the old Session("variable") = value syntax.
> (also
> > > very aware of scalability issues - so don't flame me on this - I'm
just
> > > trying to understand how the whole thing fits together here). I
expected
> > > things to work similarly with ASP.Net but I just can't get it to work
> > easily
> > > for me..
> > > > I'm trying to carry around a Session("login_id") type variable & would
> > like
> > > to access it via code-behind (.aspx.vb) modules as well as class
(.vb)
> > > modules. I can successfully set a variable in a Page_Load event from
one
> > > form (during postback) but after re-directing to another form, I get a
> > nasty
> > > error when trying to access the value:
> > > > Object reference not set to an instance of an object
> > > Line 29: Dim LoginID As String
> > > Line 30: LoginID = Session("LoginID").ToString
> > > > Source File: ... home.aspx.vb Line: 30
> > > > I've tried using HttpContext.Current.Session("LoginID").ToString but
> this
> > > just gets the same problem.
> > > > Why do I get an Object reference not set error? Surely Session doesn't
> > need
> > > to be instanced does it?
> > > > I'd appreciate any help.
> > > > Regards,
> > > Greg Linwood
> > > SQL Server MVP
> >
hmm - that's what I did..

Perhaps I'm stuffing something up in my config or somewhere else in my
code.. I'll keep on debugging & try to identify whatever.. :c/

Regards,
Greg Linwood
SQL Server MVP

"Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com> wrote in
message news:#n#vhfMsDHA.1996@.TK2MSFTNGP09.phx.gbl...
> Try server.transfer(page.aspx, true).
> Are you transferring to a page hosted in the application directory? That
> should work otherwise the problem lies elsewhere.
> regards
> --
>
> ----
> Got TidBits?
> Get it here: www.networkip.net/tidbits
> "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote in
> message news:efMJYVMsDHA.640@.tk2msftngp13.phx.gbl...
> > Thanks Alvin - but that didn't work.
> > I changed my Response.Redirect to a Server.Transfer(page, True) and I
> still
> > get the same error...
> > I noticed that the bPreserveForm argument seems only to apply to
> QueryString
> > & Form state. I want to preserve variable values in Session state,
> similarly
> > to the manner in which ASP Session worked. Is this possible in ASP.Net?
> > Perhaps there's simply some setting I'm not getting right or something..
> > Regards,
> > Greg Linwood
> > SQL Server MVP
> > "Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com> wrote
in
> > message news:ePvc9KMsDHA.2304@.tk2msftngp13.phx.gbl...
> > > when you transfer to another page, it isn't gauranteed to occur on the
> > same
> > > calling thread so all your state information, including session is
> > discarded
> > > and a new session built up to service the transfer call. If you want
to
> > > return state, there is an overloaded function parameter which enables
> you
> > to
> > > do so. Server.Transfer(page, bPreserveForm) set this to true and you
> will
> > be
> > > alright. the default is false. Same deal for redirect.
> > > > regards
> > > > --
> > > > > ----
> > > Got TidBits?
> > > Get it here: www.networkip.net/tidbits
> > > "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote
> in
> > > message news:OcFr9EMsDHA.1884@.TK2MSFTNGP10.phx.gbl...
> > > > I'm having difficulty understanding Session state in ASP.Net. It's
> > almost
> > > > embarrassing asking this as I've been using ASP since it was first
> > > released
> > > > & it really shouldn't be this hard to use - perhaps I'm just not
very
> > > smart
> > > > or perhaps MS is making this too hard for us sql bunnies to
> understand -
> > I
> > > > dunno, but I'd really appreciate someone explaining what I'm doing
> wrong
> > > > here & perhaps suggest a better approach..
> > > > > > I'm familiar with use of the old Session("variable") = value syntax.
> > (also
> > > > very aware of scalability issues - so don't flame me on this - I'm
> just
> > > > trying to understand how the whole thing fits together here). I
> expected
> > > > things to work similarly with ASP.Net but I just can't get it to
work
> > > easily
> > > > for me..
> > > > > > I'm trying to carry around a Session("login_id") type variable &
would
> > > like
> > > > to access it via code-behind (.aspx.vb) modules as well as class
> (.vb)
> > > > modules. I can successfully set a variable in a Page_Load event from
> one
> > > > form (during postback) but after re-directing to another form, I get
a
> > > nasty
> > > > error when trying to access the value:
> > > > > > Object reference not set to an instance of an object
> > > > Line 29: Dim LoginID As String
> > > > Line 30: LoginID = Session("LoginID").ToString
> > > > > > Source File: ... home.aspx.vb Line: 30
> > > > > > I've tried using HttpContext.Current.Session("LoginID").ToString but
> > this
> > > > just gets the same problem.
> > > > > > Why do I get an Object reference not set error? Surely Session
doesn't
> > > need
> > > > to be instanced does it?
> > > > > > I'd appreciate any help.
> > > > > > Regards,
> > > > Greg Linwood
> > > > SQL Server MVP
> > > > > >
I think I may have an explanation:

I think that my code: Session("LoginID").ToString breaks if "LoginID" is not
in the HttpContext.Current.Session.Keys collection because there is no
object to call .ToString against.

Does this sound like a fair explanation? If so, how does one code
defensively around this issue without writing copious amounts of spag code
to handle session variables instances not being present?

Regards,
Greg Linwood
SQL Server MVP

"Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote in
message news:uscsIZNsDHA.560@.TK2MSFTNGP11.phx.gbl...
> hmm - that's what I did..
> Perhaps I'm stuffing something up in my config or somewhere else in my
> code.. I'll keep on debugging & try to identify whatever.. :c/
> Regards,
> Greg Linwood
> SQL Server MVP
> "Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com> wrote in
> message news:#n#vhfMsDHA.1996@.TK2MSFTNGP09.phx.gbl...
> > Try server.transfer(page.aspx, true).
> > Are you transferring to a page hosted in the application directory? That
> > should work otherwise the problem lies elsewhere.
> > regards
> > --
> > ----
> > Got TidBits?
> > Get it here: www.networkip.net/tidbits
> > "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote
in
> > message news:efMJYVMsDHA.640@.tk2msftngp13.phx.gbl...
> > > Thanks Alvin - but that didn't work.
> > > > I changed my Response.Redirect to a Server.Transfer(page, True) and I
> > still
> > > get the same error...
> > > > I noticed that the bPreserveForm argument seems only to apply to
> > QueryString
> > > & Form state. I want to preserve variable values in Session state,
> > similarly
> > > to the manner in which ASP Session worked. Is this possible in
ASP.Net?
> > > Perhaps there's simply some setting I'm not getting right or
something..
> > > > Regards,
> > > Greg Linwood
> > > SQL Server MVP
> > > > "Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com> wrote
> in
> > > message news:ePvc9KMsDHA.2304@.tk2msftngp13.phx.gbl...
> > > > when you transfer to another page, it isn't gauranteed to occur on
the
> > > same
> > > > calling thread so all your state information, including session is
> > > discarded
> > > > and a new session built up to service the transfer call. If you want
> to
> > > > return state, there is an overloaded function parameter which
enables
> > you
> > > to
> > > > do so. Server.Transfer(page, bPreserveForm) set this to true and you
> > will
> > > be
> > > > alright. the default is false. Same deal for redirect.
> > > > > > regards
> > > > > > --
> > > > > > > > ----
> > > > Got TidBits?
> > > > Get it here: www.networkip.net/tidbits
> > > > "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com>
wrote
> > in
> > > > message news:OcFr9EMsDHA.1884@.TK2MSFTNGP10.phx.gbl...
> > > > > I'm having difficulty understanding Session state in ASP.Net. It's
> > > almost
> > > > > embarrassing asking this as I've been using ASP since it was first
> > > > released
> > > > > & it really shouldn't be this hard to use - perhaps I'm just not
> very
> > > > smart
> > > > > or perhaps MS is making this too hard for us sql bunnies to
> > understand -
> > > I
> > > > > dunno, but I'd really appreciate someone explaining what I'm doing
> > wrong
> > > > > here & perhaps suggest a better approach..
> > > > > > > > I'm familiar with use of the old Session("variable") = value
syntax.
> > > (also
> > > > > very aware of scalability issues - so don't flame me on this - I'm
> > just
> > > > > trying to understand how the whole thing fits together here). I
> > expected
> > > > > things to work similarly with ASP.Net but I just can't get it to
> work
> > > > easily
> > > > > for me..
> > > > > > > > I'm trying to carry around a Session("login_id") type variable &
> would
> > > > like
> > > > > to access it via code-behind (.aspx.vb) modules as well as class
> > (.vb)
> > > > > modules. I can successfully set a variable in a Page_Load event
from
> > one
> > > > > form (during postback) but after re-directing to another form, I
get
> a
> > > > nasty
> > > > > error when trying to access the value:
> > > > > > > > Object reference not set to an instance of an object
> > > > > Line 29: Dim LoginID As String
> > > > > Line 30: LoginID = Session("LoginID").ToString
> > > > > > > > Source File: ... home.aspx.vb Line: 30
> > > > > > > > I've tried using HttpContext.Current.Session("LoginID").ToString
but
> > > this
> > > > > just gets the same problem.
> > > > > > > > Why do I get an Object reference not set error? Surely Session
> doesn't
> > > > need
> > > > > to be instanced does it?
> > > > > > > > I'd appreciate any help.
> > > > > > > > Regards,
> > > > > Greg Linwood
> > > > > SQL Server MVP
> > > > > > > > > > > >
I too have been having problems with Session Variables at some servers--they
do not persist after, say, 20 seconds. But your problem is different.

And your code produces no problem when tested on my computer--the session
variable displays fine after a server.transfer or response.redirect.

What do you have in your web.config file as regards session state. Here is
what I have (watch word wrap).

<sessionState
mode="InProc"
stateConnectionString="tcpip=127.0.0.1:42424"
sqlConnectionString="data source=127.0.0.1;user id=sa;password="
cookieless="false"
timeout="60"
/
What is this "nasty error" you are receiving?

"Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote in
message news:OcFr9EMsDHA.1884@.TK2MSFTNGP10.phx.gbl...
> I'm having difficulty understanding Session state in ASP.Net. It's almost
> embarrassing asking this as I've been using ASP since it was first
released
> & it really shouldn't be this hard to use - perhaps I'm just not very
smart
> or perhaps MS is making this too hard for us sql bunnies to understand - I
> dunno, but I'd really appreciate someone explaining what I'm doing wrong
> here & perhaps suggest a better approach..
> I'm familiar with use of the old Session("variable") = value syntax. (also
> very aware of scalability issues - so don't flame me on this - I'm just
> trying to understand how the whole thing fits together here). I expected
> things to work similarly with ASP.Net but I just can't get it to work
easily
> for me..
> I'm trying to carry around a Session("login_id") type variable & would
like
> to access it via code-behind (.aspx.vb) modules as well as class (.vb)
> modules. I can successfully set a variable in a Page_Load event from one
> form (during postback) but after re-directing to another form, I get a
nasty
> error when trying to access the value:
> Object reference not set to an instance of an object
> Line 29: Dim LoginID As String
> Line 30: LoginID = Session("LoginID").ToString
> Source File: ... home.aspx.vb Line: 30
> I've tried using HttpContext.Current.Session("LoginID").ToString but this
> just gets the same problem.
> Why do I get an Object reference not set error? Surely Session doesn't
need
> to be instanced does it?
> I'd appreciate any help.
> Regards,
> Greg Linwood
> SQL Server MVP
It will break with a null reference exception if login_id isn't there like
you said. Before touching session variables you should always test:
if(Session("login_id") != null) blah blah blah. But that doesn't explain why
it isn't there after the transfer in the first place. I've written a small
demo with a transfer and redirect. No matter how you transfer, session
variables will still be around unless you explicitly clear them. Are you
clearing it somewhere after the transfer? Otherwise, you will need to
examine your IIS settings adjusting the recycle properties as needed.

One more thing you can try is to put code in you session end event to
populate a static variable. Then try to read this variable on the page you
transferred to. Session end should never be called under these
circumstances, otherwise it is the reason for your lost session variables.

Regards

--

----
Got TidBits?
Get it here: www.networkip.net/tidbits
"Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote in
message news:urAKzoNsDHA.2360@.TK2MSFTNGP10.phx.gbl...
> I think I may have an explanation:
> I think that my code: Session("LoginID").ToString breaks if "LoginID" is
not
> in the HttpContext.Current.Session.Keys collection because there is no
> object to call .ToString against.
> Does this sound like a fair explanation? If so, how does one code
> defensively around this issue without writing copious amounts of spag code
> to handle session variables instances not being present?
> Regards,
> Greg Linwood
> SQL Server MVP
> "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote in
> message news:uscsIZNsDHA.560@.TK2MSFTNGP11.phx.gbl...
> > hmm - that's what I did..
> > Perhaps I'm stuffing something up in my config or somewhere else in my
> > code.. I'll keep on debugging & try to identify whatever.. :c/
> > Regards,
> > Greg Linwood
> > SQL Server MVP
> > "Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com> wrote
in
> > message news:#n#vhfMsDHA.1996@.TK2MSFTNGP09.phx.gbl...
> > > Try server.transfer(page.aspx, true).
> > > Are you transferring to a page hosted in the application directory?
That
> > > should work otherwise the problem lies elsewhere.
> > > > regards
> > > > --
> > > > > ----
> > > Got TidBits?
> > > Get it here: www.networkip.net/tidbits
> > > "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote
> in
> > > message news:efMJYVMsDHA.640@.tk2msftngp13.phx.gbl...
> > > > Thanks Alvin - but that didn't work.
> > > > > > I changed my Response.Redirect to a Server.Transfer(page, True) and
I
> > > still
> > > > get the same error...
> > > > > > I noticed that the bPreserveForm argument seems only to apply to
> > > QueryString
> > > > & Form state. I want to preserve variable values in Session state,
> > > similarly
> > > > to the manner in which ASP Session worked. Is this possible in
> ASP.Net?
> > > > Perhaps there's simply some setting I'm not getting right or
> something..
> > > > > > Regards,
> > > > Greg Linwood
> > > > SQL Server MVP
> > > > > > "Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com>
wrote
> > in
> > > > message news:ePvc9KMsDHA.2304@.tk2msftngp13.phx.gbl...
> > > > > when you transfer to another page, it isn't gauranteed to occur on
> the
> > > > same
> > > > > calling thread so all your state information, including session is
> > > > discarded
> > > > > and a new session built up to service the transfer call. If you
want
> > to
> > > > > return state, there is an overloaded function parameter which
> enables
> > > you
> > > > to
> > > > > do so. Server.Transfer(page, bPreserveForm) set this to true and
you
> > > will
> > > > be
> > > > > alright. the default is false. Same deal for redirect.
> > > > > > > > regards
> > > > > > > > --
> > > > > > > > > > > ----
> > > > > Got TidBits?
> > > > > Get it here: www.networkip.net/tidbits
> > > > > "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com>
> wrote
> > > in
> > > > > message news:OcFr9EMsDHA.1884@.TK2MSFTNGP10.phx.gbl...
> > > > > > I'm having difficulty understanding Session state in ASP.Net.
It's
> > > > almost
> > > > > > embarrassing asking this as I've been using ASP since it was
first
> > > > > released
> > > > > > & it really shouldn't be this hard to use - perhaps I'm just not
> > very
> > > > > smart
> > > > > > or perhaps MS is making this too hard for us sql bunnies to
> > > understand -
> > > > I
> > > > > > dunno, but I'd really appreciate someone explaining what I'm
doing
> > > wrong
> > > > > > here & perhaps suggest a better approach..
> > > > > > > > > > I'm familiar with use of the old Session("variable") = value
> syntax.
> > > > (also
> > > > > > very aware of scalability issues - so don't flame me on this -
I'm
> > > just
> > > > > > trying to understand how the whole thing fits together here). I
> > > expected
> > > > > > things to work similarly with ASP.Net but I just can't get it to
> > work
> > > > > easily
> > > > > > for me..
> > > > > > > > > > I'm trying to carry around a Session("login_id") type variable &
> > would
> > > > > like
> > > > > > to access it via code-behind (.aspx.vb) modules as well as
class
> > > (.vb)
> > > > > > modules. I can successfully set a variable in a Page_Load event
> from
> > > one
> > > > > > form (during postback) but after re-directing to another form, I
> get
> > a
> > > > > nasty
> > > > > > error when trying to access the value:
> > > > > > > > > > Object reference not set to an instance of an object
> > > > > > Line 29: Dim LoginID As String
> > > > > > Line 30: LoginID = Session("LoginID").ToString
> > > > > > > > > > Source File: ... home.aspx.vb Line: 30
> > > > > > > > > > I've tried using HttpContext.Current.Session("LoginID").ToString
> but
> > > > this
> > > > > > just gets the same problem.
> > > > > > > > > > Why do I get an Object reference not set error? Surely Session
> > doesn't
> > > > > need
> > > > > > to be instanced does it?
> > > > > > > > > > I'd appreciate any help.
> > > > > > > > > > Regards,
> > > > > > Greg Linwood
> > > > > > SQL Server MVP
> > > > > > > > > > > > > > > > > > > >
Thanks Alvin.

I wasn't aware that you needed to do if(Session("login_id") != null) blah
blah blah, which I guess is a new thing you have to do in a strongly typed
environment. It makes sense, because I was testing
Session("login_id").Length which would give an object instance error if the
session variable wasn't there in the first place. Previously, in ASP, you
could check Len(Session("login_id")) which would be fine as any Variant had
a length. It's just a fundamental thinig I was missing. Because I didn't
realise this, I was not being overly careful how I populated the Session
variable in the first place, which was ultimately the source of the
problem - I had an XPATH query which was wrong & caused the
Session("loginid") variable to not be populated first..

Thanks for your help though!

Regards,
Greg Linwood
SQL Server MVP

"Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com> wrote in
message news:uAcvTkRsDHA.3468@.TK2MSFTNGP11.phx.gbl...
> It will break with a null reference exception if login_id isn't there like
> you said. Before touching session variables you should always test:
> if(Session("login_id") != null) blah blah blah. But that doesn't explain
why
> it isn't there after the transfer in the first place. I've written a small
> demo with a transfer and redirect. No matter how you transfer, session
> variables will still be around unless you explicitly clear them. Are you
> clearing it somewhere after the transfer? Otherwise, you will need to
> examine your IIS settings adjusting the recycle properties as needed.
> One more thing you can try is to put code in you session end event to
> populate a static variable. Then try to read this variable on the page you
> transferred to. Session end should never be called under these
> circumstances, otherwise it is the reason for your lost session variables.
> Regards
> --
>
> ----
> Got TidBits?
> Get it here: www.networkip.net/tidbits
> "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote in
> message news:urAKzoNsDHA.2360@.TK2MSFTNGP10.phx.gbl...
> > I think I may have an explanation:
> > I think that my code: Session("LoginID").ToString breaks if "LoginID" is
> not
> > in the HttpContext.Current.Session.Keys collection because there is no
> > object to call .ToString against.
> > Does this sound like a fair explanation? If so, how does one code
> > defensively around this issue without writing copious amounts of spag
code
> > to handle session variables instances not being present?
> > Regards,
> > Greg Linwood
> > SQL Server MVP
> > "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote
in
> > message news:uscsIZNsDHA.560@.TK2MSFTNGP11.phx.gbl...
> > > hmm - that's what I did..
> > > > Perhaps I'm stuffing something up in my config or somewhere else in my
> > > code.. I'll keep on debugging & try to identify whatever.. :c/
> > > > Regards,
> > > Greg Linwood
> > > SQL Server MVP
> > > > "Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com> wrote
> in
> > > message news:#n#vhfMsDHA.1996@.TK2MSFTNGP09.phx.gbl...
> > > > Try server.transfer(page.aspx, true).
> > > > Are you transferring to a page hosted in the application directory?
> That
> > > > should work otherwise the problem lies elsewhere.
> > > > > > regards
> > > > > > --
> > > > > > > > ----
> > > > Got TidBits?
> > > > Get it here: www.networkip.net/tidbits
> > > > "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com>
wrote
> > in
> > > > message news:efMJYVMsDHA.640@.tk2msftngp13.phx.gbl...
> > > > > Thanks Alvin - but that didn't work.
> > > > > > > > I changed my Response.Redirect to a Server.Transfer(page, True)
and
> I
> > > > still
> > > > > get the same error...
> > > > > > > > I noticed that the bPreserveForm argument seems only to apply to
> > > > QueryString
> > > > > & Form state. I want to preserve variable values in Session state,
> > > > similarly
> > > > > to the manner in which ASP Session worked. Is this possible in
> > ASP.Net?
> > > > > Perhaps there's simply some setting I'm not getting right or
> > something..
> > > > > > > > Regards,
> > > > > Greg Linwood
> > > > > SQL Server MVP
> > > > > > > > "Alvin Bruney" <vapordan_spam_me_not@.hotmail_no_spamhotmail.com>
> wrote
> > > in
> > > > > message news:ePvc9KMsDHA.2304@.tk2msftngp13.phx.gbl...
> > > > > > when you transfer to another page, it isn't gauranteed to occur
on
> > the
> > > > > same
> > > > > > calling thread so all your state information, including session
is
> > > > > discarded
> > > > > > and a new session built up to service the transfer call. If you
> want
> > > to
> > > > > > return state, there is an overloaded function parameter which
> > enables
> > > > you
> > > > > to
> > > > > > do so. Server.Transfer(page, bPreserveForm) set this to true and
> you
> > > > will
> > > > > be
> > > > > > alright. the default is false. Same deal for redirect.
> > > > > > > > > > regards
> > > > > > > > > > --
> > > > > > > > > > > > > > ----
> > > > > > Got TidBits?
> > > > > > Get it here: www.networkip.net/tidbits
> > > > > > "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com>
> > wrote
> > > > in
> > > > > > message news:OcFr9EMsDHA.1884@.TK2MSFTNGP10.phx.gbl...
> > > > > > > I'm having difficulty understanding Session state in ASP.Net.
> It's
> > > > > almost
> > > > > > > embarrassing asking this as I've been using ASP since it was
> first
> > > > > > released
> > > > > > > & it really shouldn't be this hard to use - perhaps I'm just
not
> > > very
> > > > > > smart
> > > > > > > or perhaps MS is making this too hard for us sql bunnies to
> > > > understand -
> > > > > I
> > > > > > > dunno, but I'd really appreciate someone explaining what I'm
> doing
> > > > wrong
> > > > > > > here & perhaps suggest a better approach..
> > > > > > > > > > > > I'm familiar with use of the old Session("variable") = value
> > syntax.
> > > > > (also
> > > > > > > very aware of scalability issues - so don't flame me on this -
> I'm
> > > > just
> > > > > > > trying to understand how the whole thing fits together here).
I
> > > > expected
> > > > > > > things to work similarly with ASP.Net but I just can't get it
to
> > > work
> > > > > > easily
> > > > > > > for me..
> > > > > > > > > > > > I'm trying to carry around a Session("login_id") type variable
&
> > > would
> > > > > > like
> > > > > > > to access it via code-behind (.aspx.vb) modules as well as
> class
> > > > (.vb)
> > > > > > > modules. I can successfully set a variable in a Page_Load
event
> > from
> > > > one
> > > > > > > form (during postback) but after re-directing to another form,
I
> > get
> > > a
> > > > > > nasty
> > > > > > > error when trying to access the value:
> > > > > > > > > > > > Object reference not set to an instance of an object
> > > > > > > Line 29: Dim LoginID As String
> > > > > > > Line 30: LoginID = Session("LoginID").ToString
> > > > > > > > > > > > Source File: ... home.aspx.vb Line: 30
> > > > > > > > > > > > I've tried using
HttpContext.Current.Session("LoginID").ToString
> > but
> > > > > this
> > > > > > > just gets the same problem.
> > > > > > > > > > > > Why do I get an Object reference not set error? Surely Session
> > > doesn't
> > > > > > need
> > > > > > > to be instanced does it?
> > > > > > > > > > > > I'd appreciate any help.
> > > > > > > > > > > > Regards,
> > > > > > > Greg Linwood
> > > > > > > SQL Server MVP
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
Hi William

I worked this out eventually - it was a Session variable population problem
& a fundamental mis-understanding about a strongly typed issue (which wasn't
a problem in ASP). My other post goes into a little further detail.

Thanks for your response though - my web.config is configured the same as
yours, but this isn't the problem after all.

Regards,
Greg Linwood
SQL Server MVP

"William LaMartin" <lamartin@.tampabay.rr.com> wrote in message
news:#R9b8JRsDHA.2408@.tk2msftngp13.phx.gbl...
> I too have been having problems with Session Variables at some
servers--they
> do not persist after, say, 20 seconds. But your problem is different.
> And your code produces no problem when tested on my computer--the session
> variable displays fine after a server.transfer or response.redirect.
> What do you have in your web.config file as regards session state. Here
is
> what I have (watch word wrap).
> <sessionState
> mode="InProc"
> stateConnectionString="tcpip=127.0.0.1:42424"
> sqlConnectionString="data source=127.0.0.1;user
id=sa;password="
> cookieless="false"
> timeout="60"
> />
> What is this "nasty error" you are receiving?
>
> "Greg Linwood" <g_linwoodremovethisbeforeemailingme@.hotmail.com> wrote in
> message news:OcFr9EMsDHA.1884@.TK2MSFTNGP10.phx.gbl...
> > I'm having difficulty understanding Session state in ASP.Net. It's
almost
> > embarrassing asking this as I've been using ASP since it was first
> released
> > & it really shouldn't be this hard to use - perhaps I'm just not very
> smart
> > or perhaps MS is making this too hard for us sql bunnies to understand -
I
> > dunno, but I'd really appreciate someone explaining what I'm doing wrong
> > here & perhaps suggest a better approach..
> > I'm familiar with use of the old Session("variable") = value syntax.
(also
> > very aware of scalability issues - so don't flame me on this - I'm just
> > trying to understand how the whole thing fits together here). I expected
> > things to work similarly with ASP.Net but I just can't get it to work
> easily
> > for me..
> > I'm trying to carry around a Session("login_id") type variable & would
> like
> > to access it via code-behind (.aspx.vb) modules as well as class (.vb)
> > modules. I can successfully set a variable in a Page_Load event from one
> > form (during postback) but after re-directing to another form, I get a
> nasty
> > error when trying to access the value:
> > Object reference not set to an instance of an object
> > Line 29: Dim LoginID As String
> > Line 30: LoginID = Session("LoginID").ToString
> > Source File: ... home.aspx.vb Line: 30
> > I've tried using HttpContext.Current.Session("LoginID").ToString but
this
> > just gets the same problem.
> > Why do I get an Object reference not set error? Surely Session doesn't
> need
> > to be instanced does it?
> > I'd appreciate any help.
> > Regards,
> > Greg Linwood
> > SQL Server MVP