Classic ASP, <SELECT> postback, Browser Navigation

17 Jun 2009 4:35 PM

Jai Singh

I am new to Classic ASP development and web development in general. I am
working on a data entry page in Classic ASP that preservers state through the
Session object.

I have on HTML FORM <SELECT> combo that provides a list of countries.
I have wired this up to cause a postback via "<select name=""txtCountryID""
size=""1"" onchange=""mainform.submit()"">".

In the asp page I respond to this post back and I change the input type of
another data entry field based upon the current value of the txtCountryID
<SELECT> control.
Meaning, another control is switched to either an <INPUT type="text" or an
<SELECT> itself.

For example, if the Country is US then the state data entry field is a list
of predefined states via a select combo, but if Country is CN then the state
data entry field is a blank text input.

The problem that I notice is that a user can use the Browsers navigation
buttons to move back to a pre-existing page. In some situations the
following occurs...

User chooses country US and selects a state from the state select list of CA
and then changes the country to CN and the state field changes, correctly, to
an input text that is empty.

User navs to prior page via browser.

Page now displays the Country of CN with the state <SELECT> that has a value
of CA!

I detect no post-back in my page when the browser navigation occurs.

What is the proper way to create the user interaction and deal with this
problem?

Thanks in advance,
Jai Singh

17 Jun 2009 5:31 PM

Bob Barrows

Jai Singh wrote:

> I am new to Classic ASP development and web development in general.
> I am working on a data entry page in Classic ASP that preservers
> state through the Session object.
>
> I have on HTML FORM <SELECT> combo that provides a list of countries.

There is no such thing as a "<SELECT> combo" but that's just a nitpick.
What you have is a SELECT element.

Show quoteHide quote

> I have wired this up to cause a postback via "<select
> name=""txtCountryID"" size=""1"" onchange=""mainform.submit()"">".
>
> In the asp page I respond to this post back and I change the input
> type of another data entry field based upon the current value of the
> txtCountryID <SELECT> control.
> Meaning, another control is switched to either an <INPUT type="text"
> or an <SELECT> itself.
>
> For example, if the Country is US then the state data entry field is
> a list of predefined states via a select combo, but if Country is CN
> then the state data entry field is a blank text input.
>
> The problem that I notice is that a user can use the Browsers
> navigation buttons to move back to a pre-existing page. In some
> situations the following occurs...
>
> User chooses country US and selects a state from the state select
> list of CA and then changes the country to CN and the state field
> changes, correctly, to an input text that is empty.
>
> User navs to prior page via browser.
>
> Page now displays the Country of CN with the state <SELECT> that has
> a value of CA!
>
> I detect no post-back in my page when the browser navigation occurs.
>
> What is the proper way to create the user interaction and deal with
> this problem?
>

What is the intended behavior? What do you want the user to see when he
navigates back to a page in history?

--
HTH,
Bob Barrows

17 Jun 2009 6:35 PM

Jai Singh

Bob,

Well, if at all possible, I certainly would like to avoid a cached situation
in which the HTML form is displayed with mis-matched controls (i.e. Country
is
CN but has a <select> drop down of US states).

I did a little google-research and discovered some serverside scripting
techinques for controlling clientside caching.   By adding the following to
the beginning of the .asp page....

    Response.CacheControl = "no-cache"
    Response.AddHeader "Pragma", "no-cache"
    Response.AddHeader "Cache-Control", "no-cache"
    Response.AddHeader "Cache-Control", "private"
    Response.AddHeader "Cache-Control", "no-store"
    Response.AddHeader "Cache-Control", "must-revalidate"
    Response.AddHeader "Cache-Control", "max-stale=0"
    Response.AddHeader "Cache-Control", "post-check=0"
    Response.AddHeader "Cache-Control", "pre-check=0"
    Response.AddHeader "Keep-Alive", "timeout=3, max=993"
    Response.AddHeader "Expires", "Mon, 26 Jul 1997 05:00:00 GMT"
    Response.Expires = -1
    Response.Buffer = True

..the HTTP header is modified to, hopefully, prevent the client side cache of
the .asp page and thus force a postback when the Browswer's Navigation button
is utilized.

Jai Singh

Bob Barrows" wrote:
Show quoteHide quote

> What is the intended behavior? What do you want the user to see when he
> navigates back to a page in history?
> --
> HTH,
> Bob Barrows

17 Jun 2009 9:36 PM

Evertjan.

Jai Singh wrote on 17 jun 2009 in microsoft.public.inetserver.asp.general:

> Response.AddHeader "Expires", "Mon, 26 Jul 1997 05:00:00 GMT"

What's so special about this date

"Mon, 26 Jul 1997 05:00:00 GMT"

That it gives 95,900 Google hits?

Or are you all copying and copying and copying and copying
code you do not understand?

--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

18 Jun 2009 2:01 PM

Jai Singh

Evertjan,

If you are going to bother to post in a public forum whose sole purpose is
to allow developers to learn about topics and review code samples... then
please make it useful. People would not be posting here if they had all of
the answers.

When I posted previously I gave samples of techniques that I had learned
about via public forums and some of those code lines were duplicates of one
other. But, essentially, it is my understanding that they are modifying the
HTTP Header in order to notify the browser (be it IE, Safari, etc.) that it
should not cache the .asp page in utilization.

In Actuality I finally decided to use Response.AddHeader "Expires", 0.

If you have anything of educational value to contribute then please do so.

Jai Singh

Show quoteHide quote

"Evertjan." wrote:

> Jai Singh wrote on 17 jun 2009 in microsoft.public.inetserver.asp.general:
>
> > Response.AddHeader "Expires", "Mon, 26 Jul 1997 05:00:00 GMT"
>
> What's so special about this date
>
> "Mon, 26 Jul 1997 05:00:00 GMT"
>
> That it gives 95,900 Google hits?
>
> Or are you all copying and copying and copying and copying
> code you do not understand?
>
> --
> Evertjan.
> The Netherlands.
> (Please change the x'es to dots in my emailaddress)
>

17 Jun 2009 6:08 PM

Adrienne Boswell

Gazing into my crystal ball I observed =?Utf-8?B?SmFpIFNpbmdo?=
<JaiSi***@discussions.microsoft.com> writing in
Show quoteHide quote

news:6D1F3551-86A2-4D4D-83E7-BF84BD0A8C56@microsoft.com:

> I am new to Classic ASP development and web development in general. I
> am working on a data entry page in Classic ASP that preservers state
> through the Session object.
>
> I have on HTML FORM <SELECT> combo that provides a list of countries.
> I have wired this up to cause a postback via "<select
> name=""txtCountryID"" size=""1"" onchange=""mainform.submit()"">".
>
> In the asp page I respond to this post back and I change the input
> type of another data entry field based upon the current value of the
> txtCountryID
><SELECT> control.
> Meaning, another control is switched to either an <INPUT type="text"
> or an
><SELECT> itself.
>
> For example, if the Country is US then the state data entry field is a
> list of predefined states via a select combo, but if Country is CN
> then the state data entry field is a blank text input.
>
> The problem that I notice is that a user can use the Browsers
> navigation buttons to move back to a pre-existing page. In some
> situations the following occurs...
>
> User chooses country US and selects a state from the state select list
> of CA and then changes the country to CN and the state field changes,
> correctly, to an input text that is empty.
>
> User navs to prior page via browser.
>
> Page now displays the Country of CN with the state <SELECT> that has a
> value of CA!
>
> I detect no post-back in my page when the browser navigation occurs.
>
> What is the proper way to create the user interaction and deal with
> this problem?
>
> Thanks in advance,
> Jai Singh
>

ASP knows nothing of what is going on client side, and this is a client
side issue. You would be better off posting to a client side group,
perhaps alt.html or comp.lang.javascript (if you are going to post to
more than one group, please Cross post, don't multipost).

--
Adrienne Boswell at Home
Arbpen Web Site Design Services
http://www.cavalcade-of-coding.info
Please respond to the group so others can share