Codebehind unaware of select box members populated via javascript

[Allan M.]

I have a series of select boxes that must be populated
client side, because they interact with each other. The
design specification calls for these boxes to be updated
without having to make a roundtrip to the server.

The codebehind seems to be unaware of select box members
populated via javascript. So, I'm having to create my own
state management solution, (i.e. rewriting the VIEWSTATE
mechanism) to persist the state of these select boxes
after a postback occurs.

Is there an easier or better way to do this client-side?
Note: Postback is not an option. That is the way the
code was originally written, but end users were very
unhappy with round trips to server.

I need a way to be able to update controls using
javascript and include the information in the viewstate
whenever a postback occurs. Is this possible, or is
mixing client-side and server-side form manipulation code
just not done in ASP.NET?

Thanks...

 

[Ken Cox [Microsoft MVP]]

Hi Allan,

Although I haven't tried it, I'm wondering whether you could use a hidden
server-side input box as a storage area for the populated data. Unlike the
dropdownlist boxes, input boxes are meant to collect user data.

Maybe you could store the values in some type of delimited string
"blue|red|black" that you could parse on the postback and add to the
listbox?

I could be way off the mark here, but thought I would raise the possibility
in case in sparks something else that suits.

 

[Allan M.]

Yea, I've thought of that. That will work to some degree,
but it's still just a little bit less cludgy than what
I've already got working.

I wish there was a way for the codebehind to pick up what
values are populated in various dropdowns via client-side
javascript, without having to write all of these custom
code hacks.

The other option I looked at was moving all of our
existing server side control validation routines to client-
side javascript. Then the page could only be submitted
when it was actually DONE. This would prevent the need
for separate state management mechanisms for javascript
populated select boxes, because there would be no need to
redisplay the form the user fills out. Either the form is
posted processed or a client side validation script would
halt the form post.

Once again more javascript. Yuck! There's got to be a
better way to marry the robust responsiveness of client-
side scripting and server-side ASP.Net functionality.
This all-or-nothing (client-side vs. server-side) coding
methodology really bugs me!

 

[srinvas moorthy]

hi
I m not sure to which answer you are looking for. But easy
and simples way to connect a server side control to the
client side control is
<controlname>.attributes.add("<event name>","<javascript
function name>");

Hope this answer might gives you some solution.

thanks
srinivas moorthy

-----Original Message-----
Yea, I've thought of that. That will work to some degree,
but it's still just a little bit less cludgy than what
I've already got working.

I wish there was a way for the codebehind to pick up what
values are populated in various dropdowns via client-side
javascript, without having to write all of these custom
code hacks.

The other option I looked at was moving all of our
existing server side control validation routines to client-
side javascript. Then the page could only be submitted
when it was actually DONE. This would prevent the need
for separate state management mechanisms for javascript
populated select boxes, because there would be no need to
redisplay the form the user fills out. Either the form is
posted processed or a client side validation script would
halt the form post.

Once again more javascript. Yuck! There's got to be a
better way to marry the robust responsiveness of client-
side scripting and server-side ASP.Net functionality.
This all-or-nothing (client-side vs. server-side) coding
methodology really bugs me!

-----Original Message-----
Hi Allan,

Although I haven't tried it, I'm wondering whether you could use a hidden
server-side input box as a storage area for the

populated
data. Unlike the

dropdownlist boxes, input boxes are meant to collect

user

data.

Maybe you could store the values in some type of delimited string
"blue|red|black" that you could parse on the postback

and
add to the

 

[Hai]

Hi Allan,

Regarding avoiding round trips to server I had in my application to use
Javascript to generate shopping basket.
My entire section (div) basket is generated via Javascript.
Part of the code I wrote was:
parent.frames["basket'].orderdiv.innerHTML = sOrderString;

WHenever possible I write Javascript to eliminate round trip to server.

HTH

Hai

 

[Peter Blum]

The browser technology (http, etc) is designed to post to the server a very
limited set of information. The "value" attributes of data entry fields
(<input> <textarea> <select>) and cookies. The list of text in a droplist is
simply formatting, not data. So it cannot be transferred.
The suggestion was made to transfer the value using a hidden input field.
This is a very popular way of transferring data that doesn't directly appear
on the page. Microsoft uses this to post back a button's command name via
the "__doPostBack" function you see on some of your webforms.

If you are thinking of getting validation on the client side to help,
remember that many browsers do not support client-side validation. (I sell a
product called "Professional Validation And More" that supports many more
browsers than Microsoft's validators.
http://www.peterblum.com/vam/home.aspx.)

--- Peter Blum
www.PeterBlum.com
Email: (e-mail address removed)