VB.net Tutorials with Examples

When users visit Web sites it becomes necessary to maintain session related and controls related information. In an HTTP exchange between a browser and a remote host, session related information which identifies state, such as a unique session ID, information about the user's preferences or authorization level is preserved. Note that sessions are maintained in the data being exchanged.

State Management is the process by which we maintain session related information and additional information about the controls and its state. The necessity of state management arises when multiple users request for the same or different Web Pages of a Web Site. State management can be accomplished using Client Side options or the Server side options.

Session State:

This can be thought of as a hash table. Each user would represent a different key node in the hash identifying unique values. The Session variables will be clear by the application which can clear it, as well as through the timeout property in the web config file. Usually the timeout is 20 minutes by default. ASP.NET allows you to save values using session state, a storage mechanism that is accessible from all pages requested by a single Web browser session.

Session Variables are stored on the server, can hold any type of data including references, they are similar to global variables in a windows application and use HTTP cookies to store a key with which to locate user's session variables .The collection of session variables is indexed by the name of the variable or by an integer index. Session variables are created by referring to the session variable by name. You do not have to declare a session variable or explicitly add it to the collection.

Example:

'Storing informaton in session state 
Session("username") = "Ashish"
'Retrieving information from session state
Dim str As String = Session("username")

Application State:

Application State is used to store information which is shared among users of the ASP.Net web application. Application state is stored in the memory of the windows process which is processing user requests on the web server. Application state is useful in storing small amount of often-used data. If application state is used for such data instead of frequent trips to database, then it increases the response time/performance of the web application.

In ASP.Net, application state is an instance of HttpApplicationState class and it exposes key-value pairs to store information. Its instance is automatically created when a first request is made to web application by any user and same state object is being shared across all subsequent users.

Application state can be used in similar manner as session state but it should be noted that many user might be accessing application state simultaneously so any call to application state object needs to be thread safe. This can be easily achieved in ASP.Net by using lock keyword on the statements which are accessing application state object. This lock keyword places a mutually exclusive lock on the statements and only allows a single thread to access the application state at a time.

Code Sample

'Stroing information in application state
SyncLock Me
Application("username") = "william"
End SyncLock
'Retrieving value from application state
SyncLock Me
Dim str As String = Application("username").ToString()
End SyncLock