ASP.NET - difference between viewstate and global variable

difference between viewstate and global variable

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

public static class GlobalVariable
{
    /// <summary>
    /// Global variable storing important stuff.
    /// </summary>
    static string _userName;
    /// <summary>
    /// Get or set the static important data.
    /// </summary>
    public static string UserName
    {
	get
	{
	    return _userName;
	}
	set
	{
	    _userName= value;
	}
    }
}

hi,

Global variables should always be used with caution. They are the best means of storing datahttp://www.dotnetuncle.com/aspnet/72_global_variables.aspx# that has to be accessed anywhere. The most common ways of accessing global variables in ASP.NET are by using Applicahttp://www.dotnetuncle.com/aspnet/72_global_variables.aspx#tion,, Cache, and Session objects.

ViewState is a collection bag which holds key value pairs of changed control attributes. You can also utilize it to store your own values which will persist though a Page's postbacks. ViewState is a member of Page, which means it is globably accessible throughout your Page. The ViewState is loaded early on in the Page creation (life cycle), and towards the end it is encrypted and outputed into the HTML. Therefore, when you add some data to the ViewState on the first page load, that data is being stored (encrypted) in the __ViewState hidden field you'll find in the HTML source. When the page is loaded again (after you click the button), that value is decrypted and loaded into the ViewState bag, which means you'll be able to access it.

Hi,

ViewState is the variable that holds the current state of the page, which is held in a hidden field in the page (used frequently)