如何在asp.net webforms中正确实现PRG模式

Question

I have a simple three page asp.net webforms site and having an issue with the back browser button that throws the popup "...Firefox must send any information that will repeat any action.." when hitting back on the step3.aspx.

The flow is: user lands on step1.aspx, session starts, and a user quotes on a product and gets redirected to step2.aspx. On step2.aspx, you confirm the purchase by clicking an asp:Button. The OnClick event handler, btnPurchase_Click, handles the logic for purchase and redirects, Response.Redirect("step3.aspx"), to step3.aspx. Step3.aspx simply displays the confirmation page (receipt details). The session is destroyed on step3 and when the user hits the back browser button, they are prompted with the resubmit post popup. Ideally, I want the user to hit step1 on hitting back without the resubmit prompt. Each page is set to no-cache and redirects to step1 if session is invalid.

Does anyone have a suggestion for a better flow?

This site will eventually be migrated to asp.net mvc/ajax which will most likely make the PRG workflow easier to implement but for now, looking for a relatively simple way.

Answer 1

A simple solution is to never allow a page to render on postback, but instead accept/store whatever information it was posted, and then redirect to the next page (or itself).

That way if a user hits the back button, it is going back to a GET, not a POST, and avoids the popup.

Answer 2

I give this question a try. The flow you mention will obstruct the pages normal function, which you of course already have in mind. Though, i would say it can be dangerous (against the function you expect) and contraproductive. Based on what I can see from your question, I would definitively remove Page2 and Page3 and keep all logic in same and single page.

I would also be happy to hear what you are trying to avoid, with this? Is it double posts? Like a double-post of a content in a shopping cart? Partial / uncomplete inserts of data input? With the described way to affect back-buttons, you may come around one problem but rise another. A big range of browsers that can act completely different on such work-arounds.

I see two good options,

UserControl,
Create three UserControls which every each of them have each page specific logic. You can programmatically load them into the page. Ie on bnButton_Click Event. Usercontrols are loaded with LoadControl("PathToAscxFileOnDisk.ascx") .

Panels,
I would also think about three <asp:PlaceHolder></asp:PlaceHolder> or perhaps better <asp:Panel></asp:Panel> to put all logic into.

In this case you are completely free from the postback issues and can focus on moving your functions into business logic and have use the Code-File to control the flow on show/hide and populate the controls in/out from the panels/usercontrols. You can probably also control the postback / click-URL & push-enter-key.

And you mentioned Ajax,
Ajax is absolutely there to make your page stateless (which means you can work without cache, sessions, viewstate and so on. Though, the problem lies in the users possibility to navigate between pages. I would think even Ajax is of less help, while you keep the three-pages-solution.

I would personally say it is a simple task to move the aspx files into each ascx and create a aspx as a master-container. With that option you even avoid duplicate namings (like if you copy / paste the code into panels) and trouble with Page_Load flow/logic.

Answer 3

If I understand correctly you're not yet using the PRG.

On step 2, temporarily store the information and redirect to show it. How you do so depends a lot on your application: session, database, cookies, etc are all options with different caracteristics.

Then redirect to show that information.

Same goes on step 3.

If you hit back on step 3, you'll go to step 2. But given you're going back to a GET request, there won't be a warning. Like you said, your application destroys the session data on 3, so according to what you said the user would go to step3.

Maybe I'm missing something on what you said.