What is state mamagement in asp.net?

STATE MANAGEMENT

A new instance of the Web page class is created each time the page is posted to the server. In traditional Web programming, this would typically mean that all information associated with the page and the controls on the page would be lost with each round trip. For example, if a user enters information into a text box, that information would be lost in the round trip from the browser or client device to the server.

To overcome this inherent limitation of traditional Web programming, ASP.NET includes several options that help you preserve data on both a per-page basis and an application-wide basis.

State management is the process by which you maintain state and page information over multiple requests for the same or different pages.

There are 2 types State Management: 

1. Client – Side State Management This stores information on the client's computer by embedding the information into a Web page, a uniform resource locator(url), or a cookie. The techniques available to store the state information at the client end are listed down below:

COOKIE

A cookie is a small piece of text stored on user's computer. Usually, information is stored as name-value pairs. Cookies are used by websites to keep track of visitors. Every time a user visits a website, cookies are retrieved from user machine and help identify the user.

Let's see an example which makes use of cookies to customize web page.

if (Request.Cookies["UserId"] != null)
    lbMessage.text = "Dear" + Request.Cookies["UserId"].Value + ", Welcome to our website!";
else
    lbMessage.text = "Guest,welcome to our website!";

If you want to store client's information use the below code

Response.Cookies["UserId"].Value=username;

Advantages:

• Simplicity

Disadvantages:

• Cookies can be disabled on user browsers
• Cookies are transmitted for each HTTP request/response causing overhead on bandwidth
• Inappropriate for sensitive data

Hidden fields:

Hidden fields are used to store data at the page level. As its name says, these fields are not rendered by the browser. It's just like a standard control for which you can set its properties. Whenever a page is submitted to server, hidden fields values are also posted to server along with other controls on the page. Now that all the asp.net web controls have built in state management in the form of view state and new feature in asp.net 2.0 control state, hidden fields functionality seems to be redundant. We can still use it to store insignificant data. We can use hidden fields in ASP.NET pages using following syntax

protected System.Web.UI.HtmlControls.HtmlInputHidden Hidden1;

 

//to assign a value to Hidden field

Hidden1.Value="Create hidden fields";

//to retrieve a value

string str=Hidden1.Value;

Advantages:

• Simple to implement for a page specific data
• Can store small amount of data so they take less size.

Disadvantages:                     

• Inappropriate for sensitive data
• Hidden field values can be intercepted(clearly visible) when passed over a network

View State:

View State can be used to store state information for a single user. View State is a built in feature in web controls to persist data between page post backs. You can set View State on/off for each control using EnableViewState property. By default, EnableViewState property will be set to true. View state mechanism poses performance overhead. View state information of all the controls on the page will be submitted to server on each post back. To reduce performance penalty, disable View State for all the controls for which you don't need state. (Data grid usually doesn't need to maintain state). You can also disable View State for the entire page by adding EnableViewState=false to @page directive. View state data is encoded as binary Base64 - encoded which add approximately 30% overhead. Care must be taken to ensure view state for a page is smaller in size. View State can be used using following syntax in an ASP.NET web page.

// Add item to ViewState

ViewState["myviewstate"]  = myValue;

 

//Reading items from ViewState
Response.Write(ViewState["myviewstate"]);

Advantages:

• Simple for page level data
• Encrypted 
• Can be set at the control level

Disadvantages:

• Overhead in encoding View State values
• Makes a page heavy

Query strings:

·         Query strings are usually used to send information from one page to another page. They are passed along with URL in clear text. Now that cross page posting feature is back in asp.net 2.0, Query strings seem to be redundant. Most browsers impose a limit of 255 characters on URL length. We can only pass smaller amounts of data using query strings. Since Query strings are sent in clear text, we can also encrypt query values. Also, keep in mind that characters that are not valid in a URL must be encoded using Server.UrlEncode.

·         Let's assume that we have a Data Grid with a list of products, and a hyperlink in the grid that goes to a product detail page, it would be an ideal use of the Query String to include the product ID in the Query String of the link to the product details page (for example, productdetails.aspx?productid=4).

Advantages:

• Simple to Implement

Disadvantages:

• Human Readable 
• Client browser limit on URL length
• Cross paging functionality makes it redundant 
• Easily modified by end user

Application object:·         Application object is used to store data which is visible across entire application and shared across multiple user sessions. Data which needs to be persisted for entire life of application should be stored in application object.

·         In classic ASP, application object is used to store connection strings. It's a great place to store data which changes infrequently. We should write to application variable only in application_Onstart event (global.asax) or application.lock event to avoid data conflicts. Below code sample gives idea

·         Application.Lock();

·         Application["mydata"]="mydata";

·         Application.UnLock();