ASP.NET Interview preparation

Explain the ASP.NET Page Directives?

Page directives configure the runtime environment that will execute the page. The complete list of directives is as follows:

@ Assembly - Links an assembly to the current page or user control declaratively. 

@ Control - Defines control-specific attributes used by the ASP.NET page parser and compiler and can be included only in .ascx files (user controls).

@ Implements - Indicates that a page or user control implements a specified .NET Framework interface declaratively. 

@ Import - Imports a namespace into a page or user control explicitly.

@ Master - Identifies a page as a master page and defines attributes used by the ASP.NET page parser and compiler and can be included only in .master files.

@ MasterType - Defines the class or virtual path used to type the Master property of a page.

 @ OutputCache - Controls the output caching policies of a page or user control declaratively.

 @ Page - Defines page-specific attributes used by the ASP.NET page parser and compiler and can be included only in .aspx files.

 @ PreviousPageType - Creates a strongly typed reference to the source page from the target of a cross-page posting.

 @ Reference - Links a page, user control, or COM control to the current page or user control declaratively.

 @ Register - Associates aliases with namespaces and classes, which allow user controls and custom server controls to be rendered when included in a requested page or user control.

• Life cycle of an ASP .NET page.? 

Following are the events occur during ASP.NET Page Life Cycle:

1)Page_PreInit
2)Page_Init
3)Page_InitComplete
4)Page_PreLoad
5)Page_Load
6)Control Events
7)Page_LoadComplete
8)Page_PreRender
9)SaveViewState
10)Page_Render
11)Page_Unload

Among above events Page_Render is the only event which is raised by page. So we can't write code for this event. 

What is the difference between Server.Transfer and Response.Redirect?

Response.Redirect involves a roundtrip to the server whereas Server.Transfer conserves server resources by avoiding the roundtrip. It just changes the focus of the webserver to a different page and transfers the page processing to a different page.

Response.Redirect can be used for both .aspx and html pages whereas Server.Transfer can be used only for .aspx pages.

Response.Redirect can be used to redirect a user to an external websites. Server.Transfer can be used only on sites running on the same server. You cannot use Server.Transfer to redirect the user to a page running on a different server.

Response.Redirect changes the url in the browser. So they can be bookmarked. Whereas Server.Transfer retains the original url in the browser. It just replaces the contents of the previous page with the new one.

What method do you use to explicitly kill a users session?

Session.Abandon().

• how does the cookies work in asp.net? 

we know Http is an state-less protocol which is required for interaction between clinet and server .

so there is an need to remeber state of request raised by an web browser so that 
web server can recognize you have already previously visited or not.

There are two types of state management techniques:
a) Client side state management
b) Server - side statemanagement

Using cookies comes under clinet side statemanagement .In HttpResponse we write 
Cookie containing sessionId and other information within it.

when a browser made a request to the web server the same cookie is sent to the server where server recognize the session id and get other information stored to it previously. 

• what is the difference between application state and caching? 

Application Object and Cached Object both falls under Server side State Management.

Application object resides in InProc i.e. on the same server where we hosted our application.
Cache Object resides on server side/ DownStream/Client Side.

Application Object will be disposed once application will stop.
Cache Object can be disposed using Time based cache dependency.

Only one user can access Application Object at a time hence we have to lock it every time we modify it. 

• what is boxing and unboxing?

Boxing is what happens when a value-type object is assigned to a reference-type variable.
Unboxing is what happens when a reference-type variable is assigned to a value-type variable.

• What is the use of AutoWireup in asp.net?

AutoEventWireup attribute is used to set whether the events needs to be automatically generated or not.
In the case where AutoEventWireup attribute is set to false (by default) event handlers are automatically required for Page_Load or Page_Init. However when we set the value of the AutoEventWireup attribute to true the ASP.NET runtime does not require events to specify event handlers like Page_Load or Page_Init. 

• what events will occur when a page is loaded?

Below are the events occures during page load.

1) Page_PreInit
2) Page_Init
3) Page_InitComplete
4) Page_PreLoad 

• Where is the View state Data stored?

ViewState data is stored in the hidden field. When the page is submitted to the server the data is sent to the server in the form of hidden fields for each control. If the viewstate of the control is enable true the value is retained on the post back to the client when the page is post backed. 

• Where do the Cookie State and Session State information be stored?

Cookie Information will be stored in a txt file on client system under a
folder named Cookies. Search for it in your system you will find it.

Coming to Session State
As we know for every process some default space will be allocated by OS.

In case of InProc Session Info will be stored inside the process where our
application is running.
In case of StateServer Session Info will be stored using ASP.NET State Service.
In case of SQLServer Session info will be stored inside Database. Default DB
which will be created after running InstallSQLState Script is ASPState.

•  What are the different types of sessions in ASP.Net? Name them.?

Session Management can be achieved in two ways

1)InProc
2)OutProc

OutProc is again two types
1)State Server
2)SQL Server

InProcAdv.:
1) Faster as session resides in the same process as the application
2) No need to serialize the data

DisAdv.:
1) Will degrade the performance of the application if large chunk of data is stored
2) On restart of IIS all the Session info will be lost

State ServerAdv.:
1) Faster then SQL Server session management
2) Safer then InProc. As IIS restart
won't effect the session data

DisAdv.:
1) Data need to be serialized
2) On restart of ASP.NET State Service session info will be lost
3)Slower as compared to InProc

SQL ServerAdv.:
1) Reliable and Durable
2) IIS and ASP.NET State Service
restart won't effect the session data
3) Good place for storing large chunk of data

DisAdv.:
1) Data need to be serialized
2) Slower as compare to InProc and State Server
3)Need to purchase Licensed version of SQL Server

• How can exception be handled with out the use of try catch?

using Exception Management application block

or
Page_error
Application_error objects

• What is the difference between Response.Redirect and Server.Transfer.

Server.Transfer transfers page processing from one page directly to the next page without making a round-trip back to the client's browser. This provides a faster response with a little less overhead on the server.Server.Transfer does not update the clients url history list or current url.

Response.Redirect is used toredirect the user's browser to another page or site. This performs a trip back to the client where the client's browser is redirected to the new page. The user's browser history list is updated to reflect the new address.

• How we implement Web farm and Web Garden concept in ASP.NET?.

A web farm is a multi-server scenario. So we may have a server in each state of US. If the load on one server is in excess then the other servers step in to bear the brunt.
How they bear it is based on various models.
1. RoundRobin. (All servers share load equally)
2. NLB (economical)
3. HLB (expensive but can scale up to 8192 servers)
4. Hybrid (of 2 and 3).
5. CLB (Component load balancer).
A web garden is a multi-processor setup. i.e. a single server (not like the multi server above).
How to implement webfarms in .Net:
Go to web.config and
Here for mode you have 4 options.
a) Say mode inproc (non web farm but fast when you have very few customers).
b) Say mode StateServer (for webfarm)
c) Say mode SqlServer (for webfarm)
Whether to use option b or c depends on situation. StateServer is faster but SqlServer is more reliable and used for mission critical applications.
How to use webgardens in .Net:
Go to web.config and
Change the false to true. You have one more attribute that is related to webgarden in the same tag called cpuMask.

• Is there any limit for query string? means what is the maximum size?..

Servers should be cautious about depending on URI lengths above 255 bytes because some older client or proxy implementations may not properly support these lengths.

Query string length depends on browser compatability

IE supports upto 255
Firefox supports upto 4000

• What is the exact purpose of http handlers?

ASP.NET maps HTTP requests to HttpHandlers. Each HttpHandler enables processing of individual HTTP URLs or groups of URL extensions within an application. HttpHandlers have the same functionality as ISAPI extensions with a much simpler programming model

Ex
1.Default HttpHandler for all ASP.NET pages ->ASP.NET Page Handler (*.aspx)
2.Default HttpHandler for all ASP.NET service pages->ASP.NET Service Handler (*.asmx)

An HttpHandler can be either synchronous or asynchronous. A synchronous handler does not return until it finishes processing the HTTP request for which it is called. An asynchronous handler usually launches a process that can be lengthy and returns before that process finishes
After writing and compiling the code to implement an HttpHandler you must register the handler using your application's Web.config file.

• How information about the user's locale can be accessed?

The information regarding a user's locale can be accessed by using the System.Web.UI.Page.Culture property.

• What is the difference between SQL notification and SQL invalidation?

The SQL cache notification generates notifications when the data of a database changes, on which your cache item depends. The SQL cache invalidation makes a cached item invalid when the data stored in a SQL server database changes.

• What is Cross Page Posting? How is it done?

By default, ASP.NET submits a form to the same page. In cross-page posting, the form is submitted to a different page. This is done by setting the ‘PostBackUrl’ property of the button(that causes postback) to the desired page. In the code-behind of the page to which the form has been posted, use the ‘FindControl’ method of the ‘PreviousPage’ property to reference the data of the control in the first page.

• I have created a configuration setting in my web.config and have kept it at the root level. How do I prevent it from being overridden by another web.config that appears lower in the hierarchy?

By setting the element's Override attribute to false.

• How do you exclude an ASP.NET page from using Themes?

To remove themes from your page, use the EnableTheming attribute of the Page directive.

• What is use of the AutoEventWireup attribute in the Page directive ?

The AutoEventWireUp is a boolean attribute that allows automatic wireup of page events when this attribute is set to true on the page. It is set to True by default for a C# web form whereas it is set as False for VB.NET forms. Pages developed with Visual Studio .NET have this attribute set to false, and page events are individually tied to handlers.

• What happens when you change the web.config file at run time?

ASP.NET invalidates the existing cache and assembles a new cache. Then ASP.NET automatically restarts the application to apply the changes.

• Can you programmatically access IIS configuration settings?

Yes. You can use 

ADSI - Active Directory Service Interfaces

WMI - Windows Management Instrumentation

COM - Component Object model interfaces to configure IIS programmatically.

• What is an application server?

As defined in Wikipedia, an application server is a software engine that delivers applications to client computers or devices. The application server runs your server code. Some well known application servers are IIS (Microsoft), WebLogic Server (BEA), JBoss (Red Hat), WebSphere (IBM).