ASP.NET

State management basically stores the information of user/Page or object when a user makes a request on a web page, since HTTP is a protocol which doesn’t store the information during each request made by the user.so Asp.net state management is used to preserve the data.

• Client side
• Hidden Field
• View State
• Cookies
• Control State
• Query Strings
• Server side
• Session
• Application

Server Side:-

1) Session: when we want to store the data of web page over multiple requests we use session. In this technique we can store any kind of information or object in server memory it basically stores the information. The session is user specific since it stores the information of user separately. When we store data to Session state, a session cookie named is ASP.NET_SessionId is created automatically.

Example:

Storing the data in Session object

Session ["UserName"] = txtName.Text;

Retrieving the data from the Session object

Label1.Text = Session ["UserName"].ToString();

Session timeout is 20 min if we want to increase the timeout of session then we need to configure the web config

<configuration>
 <system.web>
   <sessionState timeout="60" />
 </system.web>
</configuration>

2). Application object: In application object, we can store the information at the application level rather than User level, where every user can access that information .the main disadvantage is that sometimes there is a concurrency problem, so for that, we use a lock and unlock method. So if multiple requests came for same data then only one thread can do work.

Example:

Application["Message"] = "Hello to all";

We can use an application object to count the number of visitors on that website.

Client Side:

1) Query Strings: When we want to transfer the data over the pages from the URL then we use query string, it cannot handle the huge data and it is compatible with all browsers, we cannot transfer the objects and controls in query strings, so it is not meant for transferring sensitive data through query string.

Example:

Response.Redirect( "SecondPage.aspx?Type=01&Query=Query1" );

Or if we want to use query string to transfer the data then we can encrypt the sensitive data and we can transfer the data.

2). Control State: It is used to transfer the data which is stored in controls .it is just like same as view state but here we can store the data of the controls like dropdown list`s selected items, we cannot disabled the control state if viewstate is disabled then control state works same as view state.

3). View State: It is one of the finest methods to preserve the data, in view state we can store any kind of data like controls data, and even variables and raw data, view state encrypt the data when it will render to the user, so if user wants to see the value of view state in view source it will contain the symbols only which are very hard to decrypt.

The only disadvantage is that page contains much space over the page. To handle the view state we just need to "EnableViewState = true" attribute to any control to save its state,

Example:

public class Person
{
public string FirstName {get;set;}
public string LastName {get;set;}
}
public partial class default : Web.UI.Pages
{
Person p = new Person();
p.FirstName = "Harshit";
p.LastName = "Mittal";
ViewState["PersonDetails"]=p;
}

4). Cookies: Cookies are used to identify the user on a web page whenever the user makes the request for the first time it stores that request data in the cookies and when the user visit that web page for the second time then browser check the cookies data with second request data made by the user if the result matches browser to consider them as a previous user else consider a new user.

Example: The Case of Remember me on every login page.

There are 2 types of cookies:

1. Persistence cookies
2. Non- Persistence cookies

• Persistence cookies - When we want to store the data in cookies for a specific period of time or for permanent use then we use persistence cookies

Example:

Response.Cookies["nameWithPCookies"].Value = "This is A Persistence Cookie";
Response.Cookies["nameWithPCookies"].Expires = DateTime.Now.AddSeconds(10);

• Non Persistence cookies - In this the data stored in the cookies remain in the client hard disk folder till the time the browser is running when the browser is closed then the information of cookies is lost.

Example:

Response.Cookies["nameWithNPCookies"].Value = "This is A Non Persistence Cookie";

5) Hidden Field - When we want to store the small amount of data or we can say the if want to save the single value, hidden field controls is not rendered on the client browser, it is invisible to the browser.

Example:

<asp:HiddenField ID="HiddenField1" runat="server"  />

At the server code

protected void Page_Load(object sender, EventArgs e)
{
  if (HiddenField1.Value != null)
  {
   int val= Convert.ToInt32(HiddenField1.Value) + 1;
   HiddenField1.Value = val.ToString();
   Label1.Text = val.ToString();
  }
}

This question is a regular feature in ASP.NET interview questions for senior developer, be ready to tackle it.

As we know we cannot assign the null value to any value type so for that we use nullable type where we can assign null value to the value type variables.

Syntax:  

Nullable<T> where T is a type.
Nullable type is an instance of System.Nullable<T> struct

Nullable Struct :

[Serializable]

public struct Nullable<T> where T : struct
{        
   public bool HasValue { get; } // it will return true if we assigned a value, if there is no value or if we assign a null value it will return false;
   public T Value { get; }
}
HasValue :
static void Main(string[] args)
{
   Nullable<int> i = null;
   if (i.HasValue)
       Console.WriteLine(i.Value);
   else
       Console.WriteLine("Null");
}

Example: 

[Serializable]

public struct Nullable<T> where T : struct
{        
   public bool HasValue { get; }
   public T Value { get; }
}
static void Main(string[] args)
{
   Nullable<int> i = null;
   if (i.HasValue)
       Console.WriteLine(i.Value); // or Console.WriteLine(i)
   else
       Console.WriteLine("Null");
}

Output:

Null

It will check whether an object has been assigned a value if it is having null value it will return false and the else part will be executed.

To get the value of i using the nullable type you have to use GetValueOrDefault() method to get the actual value.

static void Main(string[] args)
{
   Nullable<int> i = null;
   Console.WriteLine(i.GetValueOrDefault());
}

Extension methods allow you to add our own custom method in any custom class without modifying into it and in our custom class and it will be available throughout the application by specifying namespace only where it is defined.

Example: 

namespace ExtensionMethod
{
   public static class IntExtension
    {
       public static bool IsGreaterThan(this int i, int value)
       {
           return i > value;
       }
   }
}

Here the first parameter specifies the type on which the extension method is applicable. We are going to use this extension method on int type. So the first parameter must be int preceded with the modifier.

using ExtensionMethod;
class Program
{
   static void Main(string[] args)
   {
       int i = 10;
       bool result = i.IsGreaterThan(100);
       Console.WriteLine(result);
   }
}

Output:

False

In Throw, the original exception stack information is retained.

Example:

For Throw :

try

{
//  some operation that can fail
}
catch (Exception ex)
{
throw;
}

For Throw Ex:

In Throw Ex the original information is overridden by the External information and you will lose the original information.

try
{
// do some operation that can fail
}
catch (Exception ex)
{
// do some local cleanup
throw;
}