Develop Reference

Saving state of a web page for users

I am trying to implement a like counter. That on a click of button increases like count by one in the database and then I am changing its text to "unlike" after clicking again my value is decrementing by 1 in the database too. It all works fine untill the page is posted back.
For eg. If a user clicks like button then text of that button changes to unlike. But if the user reloads the page then. He again gets the button as "like" but not "unlike" is there anyway I can save the state even after postback in asp.net.
Thanks in advance.

You will need to store the 'like' state in a session variable if you want it available between page switches/reloads.
This might help:
https://social.msdn.microsoft.com/Forums/vstudio/en-US/e43755ba-49f1-49b9-aa68-448ecf033a62/how-do-you-store-session-variable-in-c?forum=csharpgeneral
Alternatively, get the 'like' state from the database when generating the page.
If you're still experiencing issues, your browser might be caching the page.

If you are on to Javascript, you can try SessionStorage to hold values between page refreshes. It lasts only within the lifetime of a browsers tab and automatically destroyed when the tab/ browser is closed. Values remain completely on the client side and managed by the browser.
Session Storage (W3Schools)
Ex (extracted from the above website):
// Store
sessionStorage.setItem("lastname", "Smith");
// Retrieve
document.getElementById("result").innerHTML = sessionStorage.getItem("lastname");

Remove content of asp.net session while navigating onto another page

I have a session variable that I am using on a page. I know that sessions should be used for the purpose
of storing data between different pages of a website, but I have a big dataset to store and I am using a session instead of a view state.
I would like to empty the session when I navigate to another page.
Is there a way I can do it ?
I tried setting the session variable to null on the PageUnload event, but thats not what I want.
I would like to set the session variable to null while the page is navigated to another page.
Please let me know.

You just need to call
Session.remove("nameOfSessionVariable") ;
And regarding to how to handle the "leaving page event"
You will have to write some front-end javascript to do this using
something like window.onbeforeunload(). Then you'd have to make an
AJAX call to tell your back-end that this event is happening. This
isn't foolproof, of course. A browser crash or a forced "quit" would
not fire this event.
As can be seen here C# ASP.NET Page Leaving event?

If you truly want to detect when user leaves the page - you have to do this from the client-side. Handle onbeforeunload event and make an AJAX call to clear session variable.
But this is an overkill. Consider refactoring the code to store in session smaller amount of data and only that is used between different pages.

On the page you have navigated to you can clear a session variable as follows:
Session.Remove("Name");
To abandon the session completely:
Session.Abandon();

Is there a generally accepted way to pass data from one ASP.Net form to another after validation?

I have an ASP.Net form (Page1) where the user enters some data and then clicks the submit button.
As part of Page1, I have some Validators, including a CustomValidator which needs to do its validation back on the server.
When the user clicks the submit button a post is done to Page1 and the validation routine is run on the server and as long as I check Page.IsValid in the button click routine the form knows whether things have passed or not.
When the validation doesn't pass everything properly goes back to Form1 and the error message is displayed.
When the form does pass validation, I want to pass the data that the user entered to a second form (Page2) so that Page2 can be rendered correctly based on the data the user entered on Page1.
Is there a generally accepted way, or best way, to pass the data to Page2? Here are some ways I know about:
Call Page2 with a query string: This won't work as I need the data to not be visible to the user in certain cases.
Use the PostBackUrl on the submit button to go to Page2: As far as I know, this won't work correctly because then the server side validation routines for Page1 won't be run.
Use Session Variables: I don't know of a particular reason why this would be bad.
Use Server.Transfer: I don't really have any experience with this.
I would think that this would be a pretty standard thing to do but I'm having a hard time finding any information on the correct way to do it.

If you don't have a form of secondary storage for this data, using either Session storage or Server.Transfer would work.
You might find Server.Transfer is a little neater as, this way, you'll retain your POST values across the transfer. This will potentially save you a lot of cumbersome code playing around with session state, which, depending on how complex your forms are, could open the way to all kinds of unusual behaviour that you'd have to predict and plan to deal with in advance such as what happens when a user clicks the "back" button or - if you're posting across multiple pages - what happens when a session expires (plus Servy's examples of having multiple tabs open on the same page(s), all sharing the same session). Working with session state can be messy.
Perform your validation on PostBack then, if Page.IsValid, do:
Server.Transfer("/FormPage2.aspx");
Server.Transfer preserves Request.QueryString and Request.Form, so you can pick up your POST values on FormPage2 and do whatever you need with them here - whether it be using them for conditional logic or rendering them out again as hidden fields to join them up with the values from the second page of the form (bear in mind that if you're doing this you'll have to revalidate the hidden inputs at this stage).
http://msdn.microsoft.com/en-us/library/y4k58xk7.aspx
I have used session state for handling complex forms in the past and found myself wishing I'd used Server.Transfer, which I plan to use for all similar endeavours in the future, unless I have a very good reason not to.
You might also consider using a multiview, but in my experience these can be very messy.
Hope this helps.

I think that the easiest solution would be to specify a PreviousPageType directive. It specifies a type that the page should expect to receive and you would do a normal POST to that page.
On the second page of your application, use the following directive:
<%# PreviousPageType VirtualPath="~/FirstPage.aspx" %>
You will be able to access the properties exposed and check for validity by using something like this:
if (PreviousPage != null && PreviousPage.IsValid)

Using the Session object is a standard way to pass information across forms.
#Servy gives a good explaination (in the comments below) on how Server.Transfer can help you in this case.
The other options you stated all have problems, just like you mentioned...
If you want to use Session:
In the postback of Page1 you can set the values:
Session["myVar"] = <Data you want to pass to page2>
In page2 in the OnLoad:
if (Session["myVar"] != null)
{
myVar = Session["MyVar"]
}

You can achieve this with Server.Transfer by adding a property to your page1. In your second page in page_load for example:
Page1 prev = Page.PreviousPage as Page1;
if (prev != null)
{
// access your property here and set up the page
}

Server.Transfer can safely receive a query string without fear of the user seeing it.
Instead of Session use Context.Items.
Context.Items["validationProblems"] = "...";
Server.Transfer("FixProblems.aspx");
My other comment is that in my experience it's more "standard" to keep the validation UI contained in the same form that's collecting the information. This enables "real time" feedback. In practice I think it's better to give a user information that their doing something wrong as early as possible.
Note, that's just in my experience though.. it's a big world.

It may be more that you presently require, but one alternative is to save the data in a database:
http://msdn.microsoft.com/en-us/library/6tc47t75%28v=VS.100%29.aspx
http://www.asp.net/web-forms/videos/how-do-i/how-do-i-set-up-the-sql-membership-provider

Sesssion Variables and preventing asp:button from reloading page

I don't really have a real world problem, yet, but I'm trying to learn more about Context.Session[] variables and the postback mechanism by writing a basic little image deally. To do this I have an asp:image control with the ImageUrl set to "image.aspx" on my test.aspx page.
image.aspx simply reads the Context.Session["test"] variable and calls the gfx.DrawString(Context.Session["test"],...) to a canvas. This part is easy.
Then on test.aspx I also have an asp:button. When the button is pressed, the OnClick method changes the Context.Session["test"] to the current time using DateTime.Now.
Now here is what I'm trying to do. I want the button to perform a postback so that it can update Context.Session["test"] variable but I don't want the page to reload, then in javascript I want to refresh the src field on the image after a small time delay to allow the session variable to change.
I'm essentially trying to update the session variable and the image on the button click without the page appearing to reload.
Is it even possible to update session variables without a page refresh?
Is this possible, or am I completely off base?

To update session variables, you have to get to the server - which is where they are.
To get to the server without page appearing to reload, use AJAX.
There are various ways to use AJAX the most basic using the XMLHTTPRequest and XMLHTTPResponse classes.

MultiViewControl issues

I'm presently in the process of reworking a MultiViewControl based wizard process for our web application. I am having an rough time trying to make sense of the order that events are happening (Page_Load, Init, prerender, etc). Does anyone out there on the interwebs have details on dealing with one of these controls? Please don't just say 'google' it. I've done that and have yet to find a good, comprehensive site yet.
Admittedly, I haven't really elaborated on the problems I'm having with this control, so I'll try to do that:
Primary problem is the initialization of UserControls that live in different Views. In the existing codebase, the programmer was using a combination of multiviewcontrol.ActiveViewIndex = WHATEVER and Response.Redirect("PageWithMultiView.aspx?nextstep") and it made it all very convoluted. My task is to attempt to remove the Response.Redirect calls and use only the setting of the ActiveViewIndex. Is this even possible? Also, there are some cases where I need to initialize a control in a particular view only on the initial load and not on subsequent postbacks. I can use something like the IsPostBack flag but this is only ever set to false on the initial load. Subsequent reloads IsPostBack == true. I basically want to have IsPostBack set to false for the initial load of each View. Can this be done without doing a Response.Redirect to itself?
Hopefully this will make some sense to someone out there.
Thanks.
Greg.

I am having an rough time trying to
make sense of the order that events
are happening (Page_Load, Init,
prerender, etc).
Here you have all details about ASP.NET page lifecycle and events: http://msdn.microsoft.com/en-us/library/ms178472.aspx .
In terms of MultiView - you should NEVER use Response.Redirect when you work with MultiView.
If user can not switch to previous view then you can check previous ActiveViewIndex value before setting it to the new value, e.g.
if (mv.ActiveViewIndex != newIndex)
{
// this view is displayed for the first time
}
If user can switch to the previous views, I suggest to place an information about already used views in session or by placing hidden field on the form with ids of the views that have already been displayed and to use that information instead of IsPostBack.