ASP.NET - .NET Interview Questions and Answers

1. What is ASP?

Active Server Pages (ASP), also known as Classic ASP, is a Microsoft's server-side technology, which helps in creating dynamic and user-friendly Web pages. It uses different scripting languages to create dynamic Web pages, which can be run on any type of browser. The Web pages are built by using either VBScript or JavaScript and these Web pages have access to the same services as Windows application, including ADO (ActiveX Data Objects) for database access, SMTP (Simple Mail Transfer Protocol) for e-mail, and the entire COM (Component Object Model) structure used in the Windows environment. ASP is implemented through a dynamic-link library (asp.dll) that is called by the IIS server when a Web page is requested from the server.

2. What is ASP.NET?

ASP.NET is a specification developed by Microsoft to create dynamic Web applications, Web sites, and Web services. It is a part of .NET Framework. You can create ASP.NET applications in most of the .NET compatible languages, such as Visual Basic, C#, and J#. The ASP.NET compiles the Web pages and provides much better performance than scripting languages, such as VBScript. The Web Forms support to create powerful forms-based Web pages. You can use ASP.NET Web server controls to create interactive Web applications. With the help of Web server controls, you can easily create a Web application.

3. What is the basic difference between ASP and ASP.NET?

The basic difference between ASP and ASP.NET is that ASP is interpreted; whereas, ASP.NET is compiled. This implies that since ASP uses VBScript; therefore, when an ASP page is executed, it is interpreted. On the other hand, ASP.NET uses .NET languages, such as C# and VB.NET, which are compiled to Microsoft Intermediate Language (MSIL).

4. In which event are the controls fully loaded?

Page load event guarantees that all controls are fully loaded. Controls are also accessed in Page_Init events but you will see that view state is not fully loaded during this event

5. How can we identify that the Page is Post Back?

Page object has an "IsPostBack" property, which can be checked to know that is the page posted back.

6. What is the lifespan for items stored in ViewState?

The items stored in ViewState live until the lifetime of the current page expires including the postbacks to the same page.

7. 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.

8. 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.

9. Which is the parent class of the Web server control?

The System.Web.UI.Control class is the parent class for all Web server controls.

10. Can you set which type of comparison you want to perform by the CompareValidator control?

Yes, by setting the Operator property of the CompareValidator control.

11. What is the behavior of a Web browser when it receives an invalid element?

The behavior of a Web browser when it receives an invalid element depends on the browser that you use to browse your application. Most of the browsers ignore the invalid element; whereas, some of them display the invalid elements on the page.

12. What are the advantages of the code-behind feature?

The code-behind feature of ASP.NET offers a number of advantages:

• Makes code easy to understand and debug by separating application logic from HTML tags
• Provides the isolation of effort between graphic designers and software engineers
• Removes the problems of browser incompatibility by providing code files to exist on the Web server and supporting Web pages to be compiled on demand. 

13. How do you sign out from forms authentication?

The FormsAuthentication.Signout() method is used to sign out from the forms authentication.

14. What is AutoPostBack?

If you want a control to postback automatically when an event is raised, you need to set the AutoPostBack property of the control to True.

15. What is the function of the ViewState property?

The ASP.NET 4.0 introduced a new property called ViewStateMode for the Control class. Now you can enable the view state to an individual control even if the view state for an ASP.NET page is disabled.

16. Why do you use the App_Code folder in ASP.NET?

The App_Code folder is automatically present in the project. It stores the files, such as classes, typed data set, text files, and reports. If this folder is not available in the application, you can add this folder. One of the important features of the App_Code folder is that only one dll is created for the complete folder, irrespective of how many files it contains.

17. Define a multilingual Web site.

A multilingual Web site serves content in a number of languages. It contains multiple copies for its content and other resources, such as date and time, in different languages.

18. What is an ASP.NET Web Form?

ASP.NET Web forms are designed to use controls and features that are almost as powerful as the ones used with Windows forms, and so they are called as Web forms. The Web form uses a server-side object model that allows you to create functional controls, which are executed on the server and are rendered as HTML on the client. The attribute, runat="server", associated with a server control indicates that the Web form must be processed on the server.

19. What is the difference between a default skin and a named skin?

The default skin is applied to all the Web server controls in a Web form, which are of similar type, and it does not provide a Skin ID attribute. The named skin provides a Skin ID attribute and users have to set the Skin ID property to apply it.

20. What is IIS? Why is it used?

Internet Information Services (IIS) is created by Microsoft to provide Internet-based services to ASP.NET Web applications. It makes your computer to work as a Web server and provides the functionality to develop and deploy Web applications on the server. IIS handles the request and response cycle on the Web server. It also offers the services of SMTP and FrontPage server extensions. The SMTP is used to send emails and use FrontPage server extensions to get the dynamic features of IIS, such as form handler.

21. What is Query String? What are its advantages and limitations?

The Query String helps in sending the page information to the server.

The Query String has the following advantages:

• Every browser works with Query Strings.
• It does not require server resources and so does not exert any kind of burden on the server.

The following are the limitations of Query String:

• Information must be within the limit because URL does not support many characters.
• Information is clearly visible to the user, which leads to security threats.

22. What is actually returned from server to the browser when a browser requests an .aspx file and the file is displayed?

When a browser requests an .aspx file then the server returns a response, which is rendered into a HTML string.

23. How can you display all validation messages in one control?

The ValidationSummary control displays all validation messages in one control.

24. Which two new properties are added in ASP.NET 4.0 Page class?

The two new properties added in the Page class are MetaKeyword and MetaDescription.

25. What is tracing? Where is it used?

Tracing displays the details about how the code was executed. It refers to collecting information about the application while it is running. Tracing information can help you to troubleshoot an application. It enables you to record information in various log files about the errors that might occur at run time. You can analyze these log files to find the cause of the errors.

In .NET, we have objects called Trace Listeners. A listener is an object that gets the trace output and stores it to different places, such as a window, a file on your locale drive, or a SQL Server.

The System.Diagnostics namespace contains the predefined interfaces, classes, and structures that are used for tracing. It supplies two classes, Trace and Debug, which allow you to write errors and logs related to the application execution. Trace listeners are objects that collect the output of tracing processes.

26. What is the difference between authentication and authorization?

Authentication verifies the identity of a user and authorization is a process where you can check whether or not the identity has access rights to the system. In other words, you can say that authentication is a procedure of getting some credentials from the users and verify the user's identity against those credentials. Authorization is a procedure of granting access of particular resources to an authenticated user. You should note that authentication always takes place before authorization.

27. How can you register a custom server control to a Web page?

You can register a custom server control to a Web page using the @Register directive.

28. Which ASP.NET objects encapsulate the state of the client and the browser?

The Session object encapsulates the state of the client and browser.

29. Differentiate globalization and localization.

The globalization is a technique to identify the specific part of a Web application that is different for different languages and make separate that portion from the core of the Web application. The localization is a procedure of configuring a Web application to be supported for a specific language or locale.

30. What is ViewState?

The ViewState is a feature used by ASP.NET Web page to store the value of a page and its controls just before posting the page. Once the page is posted, the first task by the page processing is to restore the ViewState to get the values of the controls.

31. Which method is used to force all the validation controls to run?

The Page.Validate() method is used to force all the validation controls to run and to perform validation.

32. Which method has been introduced in ASP.NET 4.0 to redirect a page permanently?

The RedirectPermanent() method added in ASP.NET 4.0 to redirect a page permanently. The following code snippet is an example of the RedirectPermanent() method:
RedirectPermanent("/path/Aboutus.aspx");

33. How can you send an email message from an ASP.NET Web page?

You can use the System.Net.Mail.MailMessage and the System.Net.Mail.SmtpMail classes to send an email in your Web pages. In order to send an email through your mail server, you need to create an object of the SmtpClient class and set the server name, port, and credentials.

34. What is the difference between the Response.Write() and Response.Output.Write() methods?

The Response.Write() method allows you to write the normal output; whereas, the Response.Output.Write() method allows you to write the formatted output.

35. What does the Orientation property do in a Menu control?

Orientation property of the Menu control sets the horizontal or vertical display of a menu on a Web page. By default, the orientation is vertical.

36. Differentiate between client-side and server-side validations in Web pages.

Client-side validations take place at the client end with the help of JavaScript and VBScript before the Web page is sent to the server. On the other hand, server-side validations take place at the server end.

37. How does a content page differ from a master page?

A content page does not have complete HTML source code; whereas a master page has complete HTML source code inside its source file.

38. Suppose you want an ASP.NET function (client side) executed on the MouseOver event of a button. Where do you add an event handler?

The event handler is added to the Add() method of the Attributes property.

39. What is the default timeout for a Cookie?

The default time duration for a Cookie is 30 minutes.

40. What are HTTP handlers in ASP.NET?

HTTP handlers, as the name suggests, are used to handle user requests for Web application resources. They are the backbone of the request-response model of Web applications. There is a specific event handler to handle the request for each user request type and send back the corresponding response object.

Each user requests to the IIS Web server flows through the HTTP pipeline, which refers to a series of components (HTTP modules and HTTP handlers) to process the request. HTTP modules act as filters to process the request as it passes through the HTTP pipeline. The request, after passing through the HTTP modules, is assigned to an HTTP handler that determines the response of the server to the user request. The response then passes through the HTTP modules once again and is then sent back to the user.

You can define HTTP handlers in the <httpHandlers> element of a configuration file. The <add> element tag is used to add new handlers and the <remove> element tag is used to remove existing handlers. To create an HTTP handler, you need to define a class that implements the IHttpHandler interface.

41. What are the events that happen when a client requests an ASP.NET page from IIS server?

The following events happen when a client requests an ASP.NET page from the IIS server:

1. User requests for an application resource.
2. The integrated request-processing pipeline receives the first user request.
3. Response objects are created for each user request.
4. An object of the HttpApplication class is created and allocated to the Request object.
5. The HttpApplication class processes the user request.

42. Explain file-based dependency and key-based dependency.

In file-based dependency, you have to depend on a file that is saved in a disk. In key-based dependency, you have to depend on another cached item.

43. How can you implement the postback property of an ASP.NET control?

You need to set the AutoPostBack property to True to implement the PostBack property of controls.

44. Explain how Cookies work. Give an example of Cookie abuse.

The server tells the browser to put some files in a cookie, and the client then sends all the cookies for the domain in each request. An example of cookie abuse is large cookies affecting the network traffic.

45. Explain login controls.

Login controls are built-in controls in ASP.Net for providing a login solution to ASP.NET application. The login controls use the membership system to authenticate a user credentials for a Web site.

There are many controls in login controls.

• ChangePassword control - Allows users to change their password.
• CreateUserWizard control - Provides an interface to the user to register for that Web site.
• Login control - Provides an interface for user authentication. It consists of a set of controls, such as TextBox, Label, Button, CheckBox, HyperLink.
• LoginView control - Displays appropriate information to different users according to the user's status.
• LoginStatus control - Shows a login link to users, who are not authenticated and logout link, who are authenticated
• LoginName control - Displays a user name, if the user logs in.
• PasswordRecovery control - Allows users to get back the password through an e-mail, if they forget.

46. What is the use of PlaceHolder control? Can we see it at runtime?

The PlaceHolder control acts as a container for those controls that are dynamically generated at runtime. We cannot see it at runtime because it does not produce any visible output. It used only as a container.

47. What setting must be added in the configuration file to deny a particular user from accessing the secured resources?

To deny a particular user form accessing the secured resources, the web.config file must contain the following code:

<authorization >
<deny users="username" />
</authorization>

48. What are the event handlers that can be included in the Global.asax file?

The Global.asax file contains some of the following important event handlers:

• Application_Error
• Application_Start
• Application_End
• Session_Start
• Session_End

 
  49. What is the difference between page-level caching and fragment caching?

50. Make a list of all templates of the Repeater control.

The Repeater control contains the following templates:

• ItemTemplate
• AlternatingltemTemplate
• SeparatorTemplate
• HeaderTemplate
• FooterTemplate

51. Describe the complete lifecycle of a Web page.

When we execute a Web page, it passes from the following stages, which are collectively known as Web page lifecycle:

• Page request - During this stage, ASP.NET makes sure the page either parsed or compiled and a cached version of the page can be sent in response
• Start - During this stage sets the Request and Response page properties and the page check the page request is either a postback or a new request
• Page Initialization - During this stage, the page initialize and the control's Unique Id property are set
• Load - During this stage, if the request is postback, the control properties are loaded without loading the view state and control state otherwise loads the view state
• Validation - During this stage, the controls are validated
• Postback event handling - During this stage, if the request is a postback, handles the event
• Rendering - During this stage, the page invokes the Render method to each control for return the output
• Unload - During this stage, when the page is completely rendered and sent to the client, the page is unloaded.

52. How can you assign page specific attributes in an ASP.NET application?

The @Page directive is responsible for this.

53. Which method is used to post a Web page to another Web page?

The Respose.Redirect method is used to post a page to another page, as shown in the following code snippet: Response.Redirect("DestinationPageName.aspx");

54. What is a Cookie? Where is it used in ASP.NET?

Cookie is a lightweight executable program, which the server posts to client machines. Cookies store the identity of a user at the first visit of the Web site and validate them later on the next visits for their authenticity. The values of a cookie can be transferred between the user's request and the server's response.

 
In the page-level caching, an entire Web page is cached; whereas, in the fragment caching, a part of the Web page, such as a user control added to the Web page, is cached.

55. What are Custom User Controls in ASP.NET?

The custom user controls are the controls that are defined by developers. These controls are a mixture of custom behavior and predefined behavior. These controls work similar to other Web server controls.

56. What does the .WebPart file do?

The .WebPart file explains the settings of a Web Parts control that can be included to a specified zone on a Web page.

57. How can you enable impersonation in the web.config file?

To enable impersonation in the web.confing file, you need to include the <identity> element in the web.config file and set the impersonate attribute to true as shown in the following code snippet:
<identity impersonate = "true" />

58. How can you identify that the page is PostBack?

The Page object uses the IsPostBack property to check whether the page is posted back or not. If the page is postback, this property is set to true.

59. In which database is the information, such as membership, role management, profile, and Web parts personalization, stored?

The aspnetdb database stores all information.

60. What is State Management? How many ways are there to maintain a state in .NET?

State management is used to store information requests. The state management is used to trace the information or data that affect the state of the applications.

There are two ways to maintain a state in .NET, Client-Based state management and Server-Based state management.

The following techniques can be used to implement the Client-Based state management:

• View State
• Hidden Fields
• Cookies
• Query Strings
• Control State

The following techniques can be used to implement Server-Based state management:

• Application State
• Session State
• Profile Properties 

61. What do you understand by aggregate dependency?

Aggregate dependency allows multiple dependencies to be aggregated for content that depends on more than one resource. In such type of dependency, you need to depend on the sum of all the defined dependencies to remove a data item from the cache.

62. How can you ensure that no one has tampered with ViewState in a Web page?

To ensure that no one has tampered with ViewState in a Web page, set the EnableViewStateMac property to True.

63. What is the difference between adding items into cache through the Add() method and through the Insert() method?

Both methods work in a similar way except that the Cache.Add() function returns an object that represents the item you added in the cache. The Cache.Insert() function can replace an existing item in the cache, which is not possible using the Cache.Add() method.

64. Explain the cookie less session and its working.

ASP.NET manages the session state in the same process that processes the request and does not create a cookie. It is known as a cookie less session. If cookies are not available, a session is tracked by adding a session identifier to the URL. The cookie less session is enabled using the following code snippet: <sessionState cookieless="true" />

65. What is a round trip?

The trip of a Web page from the client to the server and then back to the client is known as a round trip.

66. What are the major built-in objects in ASP.NET?

The major built-in objects in ASP.NET are as follows:

• Application
• Request
• Response
• Server
• Session
• Context
• Trace
  
  

  67. Where should the data validations be performed-at the client side or at the server side and why?

  Data validations should be done primarily at the client side and the server-side validation should be avoided because it makes server task overloaded. If the client-side validation is not available, you can use server-side validation. When a user sends a request to the server, the validation controls are invoked to check the user input one by one.
  
  68. Why do we need nested master pages in a Web site?

  When we have several hierarchical levels in a Web site, then we use nested master pages in the Web site.
  
  69. How can you dynamically add user controls to a page?

  User controls can be dynamically loaded by adding a Web User Control page in the application and adding the control on this page.
  
  70. What is the appSettings Section in the web.config file?

  The web.config file sets the configuration for a Web project. The appSettings block in configuration file sets the user-defined values for the whole application.
  
  For example, in the following code snippet, the specified ConnectionString section is used throughout the project for database connection:
  
  <configuration>
  <appSettings>
  <add key="ConnectionString" value="server=indiabixserver; pwd=dbpassword; database=indiabix" />
  </appSettings>
  ...
  71. What type of code, client-side or server-side, is found in a code-behind file of a Web page?

  A code-behind file contains the server-side code, which means that the code contained in a code-behind file is executed at the server.
  72. To which class a Web form belongs to in the .NET Framework class hierarchy?

  A Web form belongs to the System.Web.UI.Page class.