Listbox does not appear in Request.Form

DropDown lists and Listboxes do not appear in the list of controls and
values passed back to the server on PostBack in Request.Form object. Can
someone confirm this to be correct and possibly answer why ?
The impact of this is that values added via javascript will never make it
back to the server side code unless one does some jiggery pokery with hidden
fields etc. If this is true, then I would like to understand the reason
behind the design decision and if this has been addressed in VS2005 ?
Cheers - Mr NHello, Mr. Newbie.
re:
> The impact of this is that values added via javascript will never make it
back to the
> server side code unless one does some jiggery pokery with hidden fields
JavaScript runs client-side and forms run server-side.
You need to pass the values to the server from your javascript,
which is running where the server will never see it.
re:
> If this is true, then I would like to understand the reason behind the des
ign decision
> and if this has been addressed in VS2005 ?
.
The reason is "by design", per the explanation above.
What I wonder is why you are still sticking to Request.Form,
instead of using the .NET native Request.Params, which returns
a combined collection of QueryString, Form, ServerVariables, and Cookies.
Request.Params works the same way in ASP.NET 1.x, 2.0 and WinFx :
http://msdn.microsoft.com/library/d...paramstopic.asp
http://msdn2.microsoft.com/en-us/library/dt24b615
http://winfx.msdn.microsoft.com/lib...uest_Params.asp
Juan T. Llibre, ASP.NET MVP
ASP.NET FAQ : http://asp.net.do/faq/
Foros de ASP.NET en Espaol : http://asp.net.do/foros/
======================================
"Mr Newbie" <here@.now.com> wrote in message news:OHsmCsDwFHA.256@.TK2MSFTNGP15.phx.gbl...[co
lor=darkred]
> DropDown lists and Listboxes do not appear in the list of controls and val
ues passed
> back to the server on PostBack in Request.Form object. Can someone confirm
this to be
> correct and possibly answer why ?
> The impact of this is that values added via javascript will never make it
back to the
> server side code unless one does some jiggery pokery with hidden fields et
c. If this is
> true, then I would like to understand the reason behind the design decisio
n and if this
> has been addressed in VS2005 ?
>
> Cheers - Mr N
>[/color]
This isn't an ASP.Net issue, it's how HTML and HTTP work. For list
controls, such as <input type="radio/checkbox" and <select> only the
SELECTED value is passed in the Request.Form. This is how the first form
worked in HTML 1.0 and how it works now.
ViewState tries to resolve this problem by taking all the values before the
page is rendered and serializing said values to a hidden field, which can
then be used to recreate the controls on postback. If you have a listbox
with 10 items, then those 10 items will be serialized to a hidden field. if
you dynamically add an 11th item using javascript to the control, the value
still won't be added to the hidden field and thus won't appear during
postback. This is neither a bug nor a limitation of ASP.Net.
You need to do some hidden field trick. It's often easier to copy the
selected value to a hidden field (assuming you need to know what the
selected value was) and then select all the values in the
Select/radio/checkbox It results in less code...
Karl
MY ASP.Net tutorials
http://www.openmymind.net/
"Mr Newbie" <here@.now.com> wrote in message
news:OHsmCsDwFHA.256@.TK2MSFTNGP15.phx.gbl...
> DropDown lists and Listboxes do not appear in the list of controls and
> values passed back to the server on PostBack in Request.Form object. Can
> someone confirm this to be correct and possibly answer why ?
> The impact of this is that values added via javascript will never make it
> back to the server side code unless one does some jiggery pokery with
> hidden fields etc. If this is true, then I would like to understand the
> reason behind the design decision and if this has been addressed in VS2005
> ?
>
> Cheers - Mr N
>
I dont think you have understood me, perhaps I did not make myself clear.
I am well aware that Javascript runs client side and web forms run server
side. The question is regarding ListBox and DropDown boxes. Why does ASP.NET
not preserve the 'STATE' of those controls ?
The point being is that controls such as TextBox's and Buttons etc have
their state preserved by using the Viewstate. For example if I add client
side a charavter to a textbox, ASP.NET will update the viewstate and whent
the form is posted back to the client. That change is reflected. However,
with ListBox and DropDown, this is not the case ( Apparently ) , the
question is why ?
This is not really anything to do with Javascript other than this is how I
would add items client side if I wanted to.
Does this make my question clearer ?
"Juan T. Llibre" <nomailreplies@.nowhere.com> wrote in message
news:OHEFz9DwFHA.3588@.tk2msftngp13.phx.gbl...
> Hello, Mr. Newbie.
> re:
> JavaScript runs client-side and forms run server-side.
> You need to pass the values to the server from your javascript,
> which is running where the server will never see it.
> re:
> .
> The reason is "by design", per the explanation above.
> What I wonder is why you are still sticking to Request.Form,
> instead of using the .NET native Request.Params, which returns
> a combined collection of QueryString, Form, ServerVariables, and Cookies.
> Request.Params works the same way in ASP.NET 1.x, 2.0 and WinFx :
> http://msdn.microsoft.com/library/d...paramstopic.asp
> http://msdn2.microsoft.com/en-us/library/dt24b615
> http://winfx.msdn.microsoft.com/lib...uest_Params.asp
>
>
> Juan T. Llibre, ASP.NET MVP
> ASP.NET FAQ : http://asp.net.do/faq/
> Foros de ASP.NET en Espaol : http://asp.net.do/foros/
> ======================================
> "Mr Newbie" <here@.now.com> wrote in message
> news:OHsmCsDwFHA.256@.TK2MSFTNGP15.phx.gbl...
>
> This isn't an ASP.Net issue, it's how HTML and HTTP work. For list
> controls, such as <input type="radio/checkbox" and <select> only the
> SELECTED value is passed in the Request.Form. This is how the first form
> worked in HTML 1.0 and how it works now.
I tried selecting a value which was added using Javascript, but this did
not get passed back either. So are you saying then that only the selected
value or values are passed back if the values were generated by asp.net ?
"Karl Seguin" <karl REMOVE @. REMOVE openmymind REMOVEMETOO . ANDME net>
wrote in message news:eYiCo%23DwFHA.460@.TK2MSFTNGP15.phx.gbl...
> ViewState tries to resolve this problem by taking all the values before
> the page is rendered and serializing said values to a hidden field, which
> can then be used to recreate the controls on postback. If you have a
> listbox with 10 items, then those 10 items will be serialized to a hidden
> field. if you dynamically add an 11th item using javascript to the
> control, the value still won't be added to the hidden field and thus won't
> appear during postback. This is neither a bug nor a limitation of
> ASP.Net.
> You need to do some hidden field trick. It's often easier to copy the
> selected value to a hidden field (assuming you need to know what the
> selected value was) and then select all the values in the
> Select/radio/checkbox It results in less code...
> Karl
> --
> MY ASP.Net tutorials
> http://www.openmymind.net/
> "Mr Newbie" <here@.now.com> wrote in message
> news:OHsmCsDwFHA.256@.TK2MSFTNGP15.phx.gbl...
>
Just to clarify in addition to my post...TextBoxes don't work like you think
they do with ViewState. The value of a textbox isn't preserved via
ViewState. Since there's only 1 value and HTML specifications say that the
value has to be passed via REquest.Form, it would be foolish for ASP.Net to
also maintain it in ViewState (waste of space).
ViewState is used where/when Request.Form can't. Namely for controls that
don't participate in the form submission (datagrid for example) as well as
controls who only partially participate in form submission (only the
selected radio input gets passed).
Karl
MY ASP.Net tutorials
http://www.openmymind.net/
"Mr Newbie" <here@.now.com> wrote in message
news:urmiGDEwFHA.596@.TK2MSFTNGP12.phx.gbl...
>I dont think you have understood me, perhaps I did not make myself clear.
> I am well aware that Javascript runs client side and web forms run server
> side. The question is regarding ListBox and DropDown boxes. Why does
> ASP.NET not preserve the 'STATE' of those controls ?
> The point being is that controls such as TextBox's and Buttons etc have
> their state preserved by using the Viewstate. For example if I add client
> side a charavter to a textbox, ASP.NET will update the viewstate and whent
> the form is posted back to the client. That change is reflected. However,
> with ListBox and DropDown, this is not the case ( Apparently ) , the
> question is why ?
> This is not really anything to do with Javascript other than this is how I
> would add items client side if I wanted to.
> Does this make my question clearer ?
>
>
> "Juan T. Llibre" <nomailreplies@.nowhere.com> wrote in message
> news:OHEFz9DwFHA.3588@.tk2msftngp13.phx.gbl...
>
OK, that makes sense I suppose. Presumably though viewstate is used with
textboxes to determine and fire the text changed event by comparing the text
before and that which is preserved in viewstate, or do I have that wrong as
well.
I dont seem to be doing very well today!
Cheers Mr N

> Just to clarify in addition to my post...TextBoxes don't work like you
> think they do with ViewState. The value of a textbox isn't preserved via
> ViewState. Since there's only 1 value and HTML specifications say that
> the value has to be passed via REquest.Form, it would be foolish for
> ASP.Net to also maintain it in ViewState (waste of space).
> ViewState is used where/when Request.Form can't. Namely for controls that
> don't participate in the form submission (datagrid for example) as well as
> controls who only partially participate in form submission (only the
> selected radio input gets passed).
See Karl's answer for specific recommendations.
Juan T. Llibre, ASP.NET MVP
ASP.NET FAQ : http://asp.net.do/faq/
Foros de ASP.NET en Espaol : http://asp.net.do/foros/
======================================
"Mr Newbie" <here@.now.com> wrote in message news:urmiGDEwFHA.596@.TK2MSFTNGP12.phx.gbl...[co
lor=darkred]
>I dont think you have understood me, perhaps I did not make myself clear.
> I am well aware that Javascript runs client side and web forms run server
side. The
> question is regarding ListBox and DropDown boxes. Why does ASP.NET not pre
serve the
> 'STATE' of those controls ?
> The point being is that controls such as TextBox's and Buttons etc have th
eir state
> preserved by using the Viewstate. For example if I add client side a chara
vter to a
> textbox, ASP.NET will update the viewstate and whent the form is posted ba
ck to the
> client. That change is reflected. However, with ListBox and DropDown, this
is not the
> case ( Apparently ) , the question is why ?
> This is not really anything to do with Javascript other than this is how I
would add
> items client side if I wanted to.
> Does this make my question clearer ?
>
>
> "Juan T. Llibre" <nomailreplies@.nowhere.com> wrote in message
> news:OHEFz9DwFHA.3588@.tk2msftngp13.phx.gbl...
>[/color]
No, I think you are right about that part :) i could look into it, but
let's say you are...can't think of how else it would do it ...nice catch!
Karl
MY ASP.Net tutorials
http://www.openmymind.net/
"Mr Newbie" <here@.now.com> wrote in message
news:eqqnjQEwFHA.3188@.TK2MSFTNGP14.phx.gbl...
> OK, that makes sense I suppose. Presumably though viewstate is used with
> textboxes to determine and fire the text changed event by comparing the
> text before and that which is preserved in viewstate, or do I have that
> wrong as well.
> I dont seem to be doing very well today!
> Cheers Mr N
>
>
>
>
No, you should be seeing the value in Request.Form
Request.Form is totally independant of ViewState or server-side this or
client-side that...it's much more basic than all of that. Whatever value is
selected, however it got there, should show up. The only thing I can think
of, without seeing code, is that ASP.Net does generate unique clientId's so
if you have
<asp:dropdownlist id="SomeId" runat="server" />
it might get rendered as
<select name="clt0:SomeId" > ... </select>
Form submission works on Name not Id, so I only showed the Name.
Anyways, you might be doing Request.Form["SomeId"] when really you should
be doing Request.Form[someId.ClientId] but that'll only happen when your
controls are nested.
Two things you can do. Turn tracing on in the page <%@. Page trace="True"
... %> and look at the output, or debug, add a breakpoint in Page_Load and
Add a Watch to REquest.Form
karl
--
MY ASP.Net tutorials
http://www.openmymind.net/
"Mr Newbie" <here@.now.com> wrote in message
news:ecZBvIEwFHA.3740@.TK2MSFTNGP14.phx.gbl...
> I tried selecting a value which was added using Javascript, but this did
> not get passed back either. So are you saying then that only the selected
> value or values are passed back if the values were generated by asp.net ?
>
>
>
> "Karl Seguin" <karl REMOVE @. REMOVE openmymind REMOVEMETOO . ANDME net>
> wrote in message news:eYiCo%23DwFHA.460@.TK2MSFTNGP15.phx.gbl...
>