Detecting Refresh or Post back in ASP.NET

The problem
There are situations where we would like to detect if the post back is from a form interaction (i.e. submit or button clicks) or is it by hitting the browser F5 refresh button. 

Many of them will jump saying how about checking 'Ispostback' value. 'IsPostback' will always have the value which was set previously. So for instance if the page was posted back before refresh, then the value will be true and if the page is not posted back before refresh, then the value will be false.

This article will first explain the fundamentals of how to solve the above problem and later this article will go in depth of how the source code looks like.

The fundamental

• Step 1 :-We have created a javascript which will generate unique fresh GUID in submit button click. This GUID will be stored in the HttpContext object.
• Step 2( User presses submit click ) :- If user presses submit button it will call the necessary javascript function to create the new fresh GUID again. 
• Step 3 :-In 'HttpHandler' or 'HttpModule' the new GUID value is checked with the old GUID value. If the values are not equal then it means this was not called from a submit click and it's a refresh event. Accordingly the HttpContext session value is set.
• Step 4 :-In the page load we can then check if this was a refresh or post back using the session variables.

3 important parts of the code

There are 3 important part of the code to be understood :-

• Javascript which generates the unique

I will not bore you about "why caching is so great"; it is assumed you already understand, at least in theory, what caching can buy you as an ASP.NET developer.

At a minimum a developer wants to be able to cache some (or possibly all) of the pages in her ASP.NET Application. The simplest way to achieve this is to add the @ OutputCache directive to the top of the .aspx file of each page:

<%@ OutputCache Duration="5" VaryByParam="none" %>

Now, that was easy, wasn't it? But - exactly what does it do? You are specifying how long the page is to be retained in the Cache with the Duration attribute, in seconds. In the above example, this page will be rendered on the first request for it, and stored in Cache. For five seconds, all subsequent requests for this page will be served from the Cache, which is hugely faster than having to go through the entire Page lifecycle, possibly combined with database access, re-render and finally serve the page HTML to the client. After five seconds, the page will again be rendered (and once again, stored in the Cache).

The VaryByParam attribute is used to define parameters that determine which cached copy of a page should be sent to the browser. If your page doesn't change, you can set this to "none".

Caching Pages Based on QueryString items

If the contents of one of your pages can vary based on the value of certain items on the querystring, which is a common technique in ASP.NET, you can populate the VaryByParam attribute with a semicolon-delimited