Asp.net State management

 There are two types of state management system in ASP.NET.

- Client-side state management
- Server-side state management

Explain client side state management system.

ASP.NET provides several techniques for storing state information on the client. These include the following:

- view state ASP.NET uses view state to track values in controls between page requests. It works within the page only. You cannot use view state value in next page.

- control state: You can persist information about a control that is not part of the view state. If view state is disabled for a control or the page, the control state will still work.

- hidden fields: It stores data without displaying that control and data to the user’s browser. This data is presented back to the server and is available when the form is processed. Hidden fields data is available within the page only (page-scoped data).

- Cookies:Cookies are small piece of information that server creates on the browser. Cookies store a value in the user’s browser that the browser sends with every page request to the web server.

- Query strings: In query strings, values are stored at the end of the URL. These values are visible to the user through his or her browser’s address bar. Query strings are not secure. You should not send secret information through the query string.

Explain server side state management system.

The following objects are used to store the information on the server:

- Application State:

This object stores the data that is accessible to all pages in a given Web application. The Application object contains global variables for your ASP.NET application.

- Cache Object: Caching is the process of storing data that is used frequently by the user. Caching increases your application’s performance, scalability, and availability. You can catch the data on the server or client.

- Session State: Session object stores user-specific data between individual requests. This object is same as application object but it stores the data about particular user.

Explain cookies with example.

A cookie is a small amount of data that server creates on the client. When a web server creates a cookie, an additional HTTP header is sent to the browser when a page is served to the browser. The HTTP header looks like this:

Set-Cookie: message=Hello. After a cookie has been created on a browser, whenever the browser requests a page from the same application in the future, the browser sends a header that looks like this:

Cookie: message=Hello

Cookie is little bit of text information. You can store only string values when using a cookie. There are two types of cookies:

- Session cookies
- Persistent cookies.

A session cookie exists only in memory. If a user closes the web browser, the session cookie delete permanently.

A persistent cookie, on the other hand, can available for months or even years. When you create a persistent cookie, the cookie is stored permanently by the user’s browser on the user’s computer.

Creating cookie

protected void btnAdd_Click(object sender, EventArgs e)
{
    Response.Cookies[“message”].Value = txtMsgCookie.Text;
}

// Here txtMsgCookie is the ID of TextBox. 
// cookie names are case sensitive. Cookie named message is different from setting a cookie named Message.

The above example creates a session cookie. The cookie disappears when you close your web browser. If you want to create a persistent cookie, then you need to specify an expiration date for the cookie.

Response.Cookies[“message”].Expires = DateTime.Now.AddYears(1);

Reading Cookies
void Page_Load()
{
if (Request.Cookies[“message”] != null)
lblCookieValue.Text = Request.Cookies[“message”].Value;
}
// Here lblCookieValue is the ID of Label Control.

Cookies with keyvalue pair

HttpCookie cookie = new HttpCookie("CookieName");
cookie.Values["key1"] = "value1";
cookie.Values["key2"] = "value2";
Response.Cookies.Add(cookie);

Describe the disadvantage of cookies.

- Cookie can store only string value.
- Cookies are browser dependent.
- Cookies are not secure.
- Cookies can store small amount of data.

What is Session object? Describe in detail.

HTTP is a stateless protocol; it can't hold the user information on web page. If user inserts some information, and move to the next page, that data will be lost and user would not able to retrieve the information. For accessing that information we have to store information. Session provides that facility to store information on server memory. It can support any type of object to store. For every user Session data store separately means session is user specific.

Storing the data in Session object.

Session [“message”] = “Hello World!”;

Retreving the data from Session object.

Label1.Text = Session[“message”].ToString();

What are the Advantages and Disadvantages of Session?

Following are the basic advantages and disadvantages of using session.

Advantages:

- It stores user states and data to all over the application.

- Easy mechanism to implement and we can store any kind of object.

- Stores every user data separately.

- Session is secure and transparent from user because session object is stored on the server.

Disadvantages:

- Performance overhead in case of large number of user, because of session data stored in server memory.

- Overhead involved in serializing and De-Serializing session Data. Because In case of StateServer and SQLServer session mode we need to serialize the object before store.

Explain Cache
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ASP.NET provides two types of caching that you can use to create high-performance Web applications. 

The first is output caching, which allows you to store dynamic page and user control responses on any HTTP 1.1 cache-capable device in the output stream, from the originating server to the requesting browser. 

The second type of caching is application data caching, which you can use to programmatically store arbitrary objects, such as application data, in server memory so that your application can save the time and resources it takes to recreate them.

Caching is implemented by the Cache class, with cache instances private to each application. The cache lifetime is tied to that of the application; when the application is restarted, the Cache object is recreated.

Add Items to the Cache

 If you use the Insert method to add an item to the cache and an item with the same name already exists, the existing item in the cache is replaced.

 if you use the Add method and an item with the same name already exists in the cache, the method will not replace the item and will not raise an exception.