Ahmed’s Dev-Shop

ASP.Net Page loading twice

Posted in .Net, programming, software by Ahmed Siddiqui on June 2, 2008

If you are observing load event twice in a post back in ASP.Net page, check the following:

  • If Page_Load handler defined in Codebehind then AutoEventWireup property should be “false”
  • Check if you have mistakenly multiple event handlers registered for an event
  • Src or ImageURL attribute of your image control are defined and not empty (you can put %20 for blank)
  • bgColor or background is empty

Last two problems usually appears in one browser while disappears in other.

How to choose from Viewstate, SessionState, Cookies and Cache

Posted in programming by Ahmed Siddiqui on April 10, 2008

Problem with Web Applications

Web applications are stateless, means once a web page is rendered from server to client, nothing in the page remains on server and the next time user submits the page, the page will be called and created from scratch.

ASP.NET provides following solutions to solve this problem:

1- Viewstate
2- Session Variables
3- Application Variables
4- Cache
5- Cookies

Now the question arises that when to use what?

1- Viewstate

Viewstate is a hidden fields in an ASP.NET page, contains state of those controls on a page whose “EnableViewstate” property is “true”.
You can also explicitly add values in it, on an ASP.NET page like:
Viewstate.Add( “TotalStudents”, “87” );
Viewstate should be used when you want to save a value between different round-trips of a single page as viewstate of a page is not accessible by another page.
Because Viewstate render with the page, it consumes bandwidth, so be careful to use it in applications to be run on low bandwidth.

2- Session Variable

Session variables are usually the most commonly used.
When a user visits a site, it’s sessions starts and when the user become idle or leave the site, the session ends.
Session variables should be used to save and retrieve user specific information required on multiple pages.
Session variables consumes server memory, so if your may have a huge amount visitors, use session very carefully and instead of put large values in it try to put IDs and references

3- Application variables

Application variables are shared variables among all users of a web application
Application variables behave like static variables and they are substitute of static variables as static variables are stateless in web applications
Only shared values should be persisted in Application variables, and as soon as they are not in use they should be removed explicitly.

4- Cache

Cache is probably the least used state feature of ASP.NET.
Cache is basically a resource specific state persistence feature, means unlike session it stick with resource instead of user, for instance: pages, controls etc.
Cache should be used or frequently used pages, controls, and data structures
Data cache can be used to cache frequently used list of values e.g. list of products

6- Cookies

Cookies are some values saved in browsers for a particular website o publicly accessible
The purpose of cookies is to help websites to identify visitors and retrieve their saved preferences
Cookies are also used to facilitate auto login by persisting user id in a cookie save in user’s browser
Because cookies have been saved at client side, they do not create performance issues but may create security issues as they can be hacked from browser

Finally remember the following points on your finger-tips:

1- Viewstate is bandwidth hungry
2- Session variables are memory hungry as per number of users
3- Applications variables are shared
4- Cache is memory hungry as per number of resources
5- Cookies are the least secure

http://www.codeproject.com/KB/aspnet/HowToChoose.aspx