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New Message on BDOTNET
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From: Sitaraman
Message 8 in Discussion
Hi There is more to it in passing values from page to page than wat meets the eye
Lets assume that Page1 has a textbox txt_data. One some submit it has to show page2
There could be two scenarios here Scenario1 : Page1 -> Data Entry in txt_Data->
Submit->Some procesing in Page1->Send the value of txt_data on a as-is-where-is
condition to Page2->Use it in Page2 This is imple. Can be done using
Session+Response.Redirect or Request Params+Server.Transfer Sample using
Session+Response.Redirect Page1 Session.Add("txt_Data", txt_Data.Text)
Response.Redirect("webform2.aspx") Page2 'Populate Data From Session
TextBox1.Text = Session("txt_Data")
Session.Remove("txt_Data") Sample Using Server.Transfer+Request params
Collection Page1 Server.Transfer("webform2.aspx", True) Page2 'txt_Data value is is
automatically transferred due to the 'true' parameter in Server.Transfer. So just get
the value from Request TextBox3.Text = Request.Params.Get("txt_Data") This is simple
But the catch is what if the scenario is different Scenario2 : Page1 -> Data Entry
in txt_Data-> Submit->Some procesing in Page1->Dynamically Generate a Value in Page1
which will be used in Page2->Send the value of txt_data on a as-is-where-is condition
+the dynamic value to Page2->Use txt_data+Dynamic Value in Page2 Here You can again
useSample using Session+Response.Redirect straightForward as above Sample using
Session+Response.Redirect Page1 Session.Add("txt_Data", txt_Data.Text)
Session.Add("hdn_hidden", "?somevalue=1")
Response.Redirect("webform2.aspx") Page2 TextBox1.Text = Session("txt_Data")
TextBox2.Text = Session("hdn_hidden")
Session.Remove("txt_Data")
Session.Remove("hdn_hidden") But due to the concurrency problems inherent in such a
usage, you might not want to use sesion. Other option is to use the following method
Sample Using Server.Transfer+Request params Collection+HTTPContext Page1 ' Form
Control Values are automatically transferred as the
' second Parameter value is true in the Server.Transfer
' So only the dynamic value to be sent has to be added
' to the context
context.Items.Add("hdn_hidden", "?someValue=2")
Server.Transfer("webform2.aspx", True) Page2 'Populate Data From Form Control
TextBox3.Text = Request.Params.Get("txt_Data")
TextBox4.Text = context.Items("hdn_hidden") Here the best part is if i use session, i
need to clear it explicitly in page2 and also you have the concurrency problems(wat if
the user opens a new window in IE using File->New->Window, in which case session will
be same). Also the data tobe passed to page2 is valid for only request. So how do i
pass it in the Server.Transfer method. The options are Add the value to a Form
Controls -> You can have a hidden control and populate the value in it and then do a
Server.Transfer. Will not work coz, when Server.Transfer is used, the params
collection( containing the servervariables, querystring, cookies, forms request etc)
will have the original value that was submitted by the Page1. Even if u put a value
in the Page1 CodeBehind before server.transfer, it is not reflected(in fact if u try
to modify any of the request.params, u will get a exception as it is readonly) and
when transfer is called, the original request.params,created at the time of page1
submit is passed, thereby losing the modification Add Modify the Request.Params for
the modified value -> Cannot be done coz, the NameValue Collection is a readonly
entity. Same applies to ServerVariables Use ViewState : Same problem as form
controls. When you use the viewstate, the viewstate passed to page2 would be the
same as the one which was created when the page1 was submitted. But our flow is that
page1 submit->ViewState acquired, addition to viewstate. In this case, when
Server.Transfer is called the original viewstate which was created on submit will be
passed to Page2 and so the modification to viewstate that we have done will be lost
Certain things to understand are 1) The flow is : Page1->Submit->Request To
server->Page Processing by Server. At this time, the viewstate, request,
servervariables are somewat frozen/baselined(a crude term, though). When
Server.transfer is called, it is this
formcollection/cookies/servervariables/viewstate that will be passed. Any modification
in these entities between the baseline time and the server.transfer call time is
irrelevant in Page2 as they will never be reflected. 2) The request.params is created
when the client request is fired and after that is totally read-only. 3) Any
modifications you do in page1 codebehind to the controls is reflected only in the
Server Controls(controls with runat=server tag). This is not reflected in the request
object 4) When Server.Transfer is called, only the built-in objects(Request, Response
etc) are passed to the called page So if you want to transfer from Page1 to Page1
and do not want to use querystring and do not want to use session and still pass a
dynamic value the best solution, i believe, is HTTPContext+Server.Transfer. The fun
part about context is that it is valid for only one request operation only. So u dont
need to cleanup the variables, whereas in session, you need to explicitly write the
code for tht. On Im attaching a small solution which makes use of the both the
Response.Redirect+Session and the Server.Transfer+RequestParams+HttpContext
mechanisms. But do note that while the Server.Transfer saves one round-trip from the
client to the server, u will have the overhead of holding all the page1 data in server
memory till the time page2 response is written . Hope this helps regards, sr
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