ASP.NET Interview Questions.

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.Ul.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, theResponse.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 asTextBox, 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?

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.

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.

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.

73. What does the "EnableViewState" property do? Why do we want it On or Off?
The EnableViewState property enables the ViewState property on the page. It is set to On to allow the page to save the users input between postback requests of a Web page; that is, between the Request and corresponding Response objects. When this property is set to Off, the page does not store the users input during postback.

74. Which event determines that all the controls are completely loaded into memory?
The Page_Load event determines that all the controls on the page are fully loaded. You can also access the controls in the Page_Init event; however, the ViewState property does not load completely during this event.

75. What is the function of the CustomValidator control?
It provides the customize validation code to perform both client-side and server-side validation.

76. What is Role-based security?
In the Role-based security, you can assign a role to every user and grant the privilege according to that role. A role is a group of principal that restricts a user's privileges. Therefore, all the organization and applications use role-based security model to determine whether a user has enough privileges to perform a requested task.

77. Which data type does the RangeValidator control support?
The data types supported by the RangeValidator control are Integer, Double, String, Currency, and Date.

78. What are the HTML server controls in ASP.NET?
 HTML server controls are similar to the standard HTML elements, which are normally used in HTML pages. They expose properties and events that can be used programmatically. To make these controls programmatically accessible, you need to specify that the HTML controls act as a server control by 

adding the runat="server"attribute.

79. Why a SiteMapPath control is referred to as breadcrumb or eyebrow navigation control?
The SiteMapPath control displays a hierarchical path to the root Web page of the Web site. Therefore, it is known as the breadcrumb or eyebrow navigation control.

 80. Where is the ViewState information stored?
The ViewState information is stored in the HTML hidden fields.

81. Which namespaces are necessary to create a localized application?
The System.Globalization and System.Resources namespaces are essential to develop a localized application.

82. What is the difference between an HtmlInputCheckBox control and an HtmlInputRadioButton control?
You can select more than one HtmlInputCheckBox control from a group of HtmlInputCheckBox controls; whereas, you can select only a single HtmllnputRadioButton control from a group of HtmlInputRadioButton controls.

83. What is the difference between HTML and Web server controls?
HTML controls are client-side controls; therefore, all the validations for HTML controls are performed at the client side. On the other hand, Web server controls are server-side controls; therefore, all the validations for Web server controls are performed at the server side.

84. Explain the AdRotator Control.
The AdRotator is an ASP.NET control that is used to provide advertisements to Web pages. The AdRotatorcontrol associates with one or many advertisements, which randomly displays one by one at a time when the Web page is refreshed. The AdRotator control advertisements are associated with links; therefore, when you click on an advertisement, it redirects you to other pages. 

The AdRotator control is associated with a data source, which is normally an xml file or a database table. A data source contains all the information, such as advertisement graphics reference, link, and alternate text. Therefore, when you use the AdRotator control, you should first create a data source and then associate it with the AdRotator control.

85. What do you understand by the culture?

The culture denotes a combination of a language and optionally a region or a country. The contents of a Web page of a multilingual Web site are changed according to the culture defined in the operating system of the user accessing the Web page.

86. What is the difference between absolute expiration and sliding-time expiration?

The absolute expiration expires a cached item after the provided expiration time. The sliding time does not expire the cached items because it increments the specified time.

87. What is the code-behind feature in ASP.NET?

The code-behind feature of ASP.NET enables you to divide an ASP.NET page into two files - one consisting of the presentation data, and the second, which is also called the code-behind file, consisting of all the business logic. The presentation data contains the interface elements, such as HTML controls and Web server controls, and the code-behind contains the event-handling process to handle the events that are fired by these controls. The file that contains the presentation data has the .aspx extension. The code behind file has either the .cs extension (if you are using the programming language C#) or the .vb (if you are using the programming language Visual Basic .NET) extension.

88. How can you check if all the validation controls on a Web page are valid and proper?

You can determine that all the validation controls on a Web page are properly working by writing code in the source file of the Web page using a scripting language, such as VBScript or JavaScript. To do this task, you have to loop across validators collection of pages and check the IsValid property of each validation control on the Web page to check whether or not the validation test is successful.

89. Explain the validation controls. How many validation controls in ASP.NET 4.0?

Validation controls are responsible to validate the data of an input control. Whenever you provide any input to an application, it performs the validation and displays an error message to user, in case the validation fails.

ASP.NET 4.0 contains the following six types of validation controls:

• CompareValidator - Performs a comparison between the values contained in two controls.
• CustomValidator - Writes your own method to perform extra validation.
• RangeValidator- Checks value according to the range of value.
• RegularExpressionValidator - Ensures that input is according to the specified pattern or not.
• RequiredFieldValidator - Checks either a control is empty or not.
• ValidationSummary - Displays a summary of all validation error in a central location.

90. What is difference between a Label control and a Literal control?

The Label control's final html code has an HTML tag; whereas, the Literal control's final html code contains only text, which is not surrounded by any HTML tag.

91. How many types of Cookies are available in ASP.NET?

There are two types of Cookies available in ASP.NET:

• Session Cookie - Resides on the client machine for a single session until the user does not log out.
• Persistent Cookie - Resides on a user's machine for a period specified for its expiry, such as 10 days, one month, and never.

The user can set this period manually.

92. What is the use of the Global.asax file?

The Global.asax file executes application-level events and sets application-level variables.

93. What are the Culture and UICulture values?

The Culture value determines the functions, such as Date and Currency, which are used to format data and numbers in a Web page. The UICulture value determines the resources, such as strings or images, which are loaded for a Web page in a Web application.

94. What is the difference between ASP session and ASP.NET session?

ASP does not support cookie-less sessions; whereas, ASP.NET does. In addition, the ASP.NET session can span across multiple servers.

95. Which control will you use to ensure that the values in two different controls match?

You should use the CompareValidator control to ensure that the values in two different controls match.

96. What is the difference between a page theme and a global theme?

A page theme is stored inside a subfolder of the App_Themes folder of a project and applied to individual Web pages of that project. Global themes are stored inside the Themes folder on a Web server and apply to all the Web applications on the Web server.

97. What do you mean by a neutral culture?

When you specify a language but do not specify the associated country through a culture, the culture is called as a neutral culture.

98. What is the use of the <sessionState> tag in the web.config file?

The <sessionState> tag is used to configure the session state features. To change the default timeout, which is 20 minutes, you have to add the following code snippet to the web.config file of an application:<sessionState timeout="40"/>

99. Can you post and access view state in another application?

Yes, you can post and access a view state in other applications. However, while posting a view state in another application, the PreviousPage property returns null.

100. Which method do you use to kill explicitly a users session?

The Session.Abandon() method kills the user session explicitly.

101. Which class is inherited when an ASP.NET server control is added to a Web form?

The System.Web.UI.WebControls class is inherited when an ASP.NET server control is added to a Web form.

102. What events are fired when a page loads?

The following events fire when a page loads:

• Init() - Fires when the page is initializing.
• LoadViewState() - Fires when the view state is loading.
• LoadPostData() - Fires when the postback data is processing.
• Load() - Fires when the page is loading.
• PreRender() - Fires at the brief moment before the page is displayed to the user as HTML.
• Unload() - Fires when the page is destroying the instances of server controls.

103. Write three common properties of all validation controls.

Three common properties of validation controls are as follows:

• ControlToValidate - Provides a control to validate
• ErrorMessage - Displays an error message
• IsValid - Specifies if the control's validation has succeeded or not
• Text - Displays a text for validation control before validation

104. What are navigation controls? How many navigation controls are there in ASP.NET 4.0?

Navigation controls help you to navigate in a Web application easily. These controls store all the links in a hierarchical or drop-down structure; thereby facilitating easy navigation in a Web application.

There are three navigation controls in ASP.Net 4.0.

• SiteMapPath
• Menu
• TreeView

105. What happens if an ASP.NET server control with event-handling routines is missing from its definition?

The compilation of the application fails.

106. What are server-side comments?

Server-side comments are included in an ASP.NET page for the purpose of documentations as shown in the following code snippet:

<%--This is an example of server-side comments --%> 

The server-side comments begin with <%-- and end with --%>.

107. How can we provide the WebParts control functionality to a server control?

We can provide the WebParts controls functionality to a server control by setting the CreateWebPart property of WebPartManger.

108. How do you prevent a validation control from validating data at the client end?

You can prohibit a validation control to validate data at the client side by setting the EnableClientScript property to False.

109. What is cross-page posting in ASP.NET?

The Server.Transfer() method is used to post data from one page to another. In this case, the URL remains the same. However, in cross page posting, data is collected from different Web pages and is displayed on a single page. To do so, you need to set the PostBackUrl property of the control, which specifies the target page. In the target page, you can access the PreviousPage property. For this, you need to use the @PreviousPageType directive. You can access the controls of previous page by using the FindControl()method.

110. Which ASP.NET configuration options are supported in the ASP.NET implementation on the shared Web hosting platform?

There are many ASP.NET configuration choices, which are not able to configure at the site, application, or child directory level on the shared hosting environment. Some options can produce security, performance, and stability problem to the server and therefore cannot be changed. 

The following settings are the only ones that can be changed in the web.config file(s) of your Web site:

• browserCaps
• clientTarget
• pages
• customErrors
• globalization
• authorization
• authentication
• webControls
• webServices

111. Explain the Application and Session objects in ASP.NET.

Application state is used to store data corresponding to all the variables of an ASP.NET Web application. The data in an application state is stored once and read several times. Application state uses theHttpApplicationState class to store and share the data throughout the application. You can access the information stored in an application state by using the HttpApplication class property. Data stored in the application state is accessible to all the pages of the application and is the same for all the users accessing the application. The HttpApplicationState class provides a lock method, which you can use to ensure that only one user is able to access and modify the data of an application at any instant of time.

Each client accessing a Web application maintains a distinct session with the Web server, and there is also some specific information associated with each of these sessions. Session state is defined in the<sessionState> element of the web.config file. It also stores the data specific to a user session in session variables. Different session variables are created for each user session. In addition, session variables can be accessed from any page of the application. When a user accesses a page, a session ID for the user is created. The session ID is transferred between the server and the client over the HTTP protocol using cookies.

112. How will you differentiate a submaster page from a top-level master page?

Similar to a content page, a submaster page also does not have complete HTML source code; whereas, a top-level master page has complete HTML source code inside its source file.

113. What are Web server controls in ASP.NET?

The ASP.NET Web server controls are objects on the ASP.NET pages that run when the Web page is requested. Many Web server controls, such as button and text box, are similar to the HTML controls. In addition to the HTML controls, there are many controls, which include complex behavior, such as the controls used to connect to data sources and display data.

114. What is the difference between a HyperLink control and a LinkButton control?

A HyperLink control does not have the Click and Command events; whereas, the LinkButton control has these events, which can be handled in the code-behind file of the Web page.

115. What are the various ways of authentication techniques in ASP.NET?

There are various techniques in ASP.NET to authenticate a user. You can use one of the following ways of authentication to select a built-in authentication provider:

• Windows Authentication - This mode works as the default authentication technique. It can work with any form of Microsoft Internet Information Services (IIS) authentication, such as Basic, Integrated Windows authentication (NTLM/Kerberos), Digest, and certificates. The syntax of Windows authentication mode is given as follows: <authentication mode="windows" />
• Forms Authentication - You can specify this mode as a default authentication mode by using the following code snippet: <authentication mode="Forms"/>
• Passport - This mode works with Microsoft Passport authentication, as shown in the following code snippet: <authentication mode = "Passport"/>

116. What are the different ways to send data across pages in ASP.NET?

The following two ways are used to send data across pages in ASP.NET:

• Session
• Public properties

117. What does the WebpartListUserControlPath property of a DeclarativeCatalogPart control do?

The WebpartListUserControlPath property sets the route of the user defined control to aDeclarativeCatalogPart control.

118. What do you mean by the Web Part controls in ASP.NET?

The Web Part controls are the integrated controls, which are used to create a Web site. These controls allow the users to change the content, outlook, and state of Web pages in a Web browser.

119. What type of the CatalogPart control enables users to restore the Web Parts that have been removed earlier by the user?

The PageCatalogPart control.

120. What is the use of web.config? What is the difference between machine.config and web.config?

ASP.NET configuration files are XML-based text files for application-level settings and are saved with the name web.config. These files are present in multiple directories on an ASP.NET Web application server. Theweb.config file sets the configuration settings to the directory it is placed in and to all the virtual sub folders under it. The settings in sub directories can optionally override or change the settings specified in the base directory.

The difference between the web.config and machine.config files is given as follows:

• <WinDir>\Microsoft.NET\Framework\<version>\config\machine.config provides default configuration settings for the entire machine. ASP.NET configures IIS to prohibit the browser directly from accessing the web.config files to make sure that their values cannot be public. Attempts to access those files cause ASP.NET to return the 403: Access Forbidden error.
• ASP.NET uses these web.config configuration files at runtime to compute hierarchically a sole collection of settings for every URL target request. These settings compute only once and cached across further requests. ASP.NET automatically checks for changing file settings and do not validate the cache if any of the configuration changes made.

121. Explain the concept of states in ASP.NET.

State is quite an innovative concept in Web development because it eliminates the drawback of losing state data due to reloading of a Web page. By using states in a Web application, you can preserve the state of the application either at the server or client end. The state of a Web application helps you to store the runtime changes that have been made to the Web application. For example, as already described earlier, a change in the data source of the Web application might be initiated by a user when he/she selects and saves some products in the shopping cart. 

If you are not using states, these changes are discarded and are not saved. You may think that the whole concept of storing states is optional. However, under certain circumstances, using states with applications is imperative. For example, it is necessary to store states for Web applications, such as an e-commerce shopping site or an Intranet site of a company, to keep track of the requests of the users for the items they have selected on the shopping site or the days requested for vacation on the Intranet site.

122. Can we validate a DropDownList by RequiredFieldValidator?

Yes, we can validate a DropDownList by RequiredFieldValidator. To perform this validation, we have to set the InitialValue property of RequiredFieldValidator control.

123. List the features of the Chart control.

The following are the features of the Chart control:

• Bounds a chart with any data source.
• Simple manipulation of chart data, such as copying, merging, grouping, sorting, searching, and filtering.
• Support many statistical and financial formulas for data analysis.
• Provide advanced chart outlook, such as 2-D, 3-D, lighting, and perspective.
• Support events and customizations.
• Includes interactivity with Microsoft AJAX.
• Supports AJAX Content Delivery Network (CDN).

Understanding the Basics of Web Service in ASP.NET

Introduction

This article aims at understanding the need for a web service, the benefits of having a web service and how we can create a basic web service and consume it.

Background

Connectivity between applications is very important. Connectivity in any case is very important for that matter but it specially is very important between applications. Connecting web application used to be a big challenge before the advent of technologies like SOAP (Simple Object Access Protocol). The reason it was so difficult was, there were so many technologies people were working in. The applications were hosted on different types of servers, etc. But these things should not be a barrier to facilitate the communication between applications. The only requirement was to have some standards to follow and standard ways of doing things so that the applications become capable of communicating with other applications irrespective of the technologies used.

SOAP and Web Services

SOAP and XML created the solution for the problem that developers were facing before. SOAP is a standard XML based protocol that communicated over HTTP. We can think of SOAP as message format for sending messaged between applications using XML. It is independent of technology, platform and is extensible too.

We have SOAP and XML to give us connectivity between applications. Does it mean that I have to write XML and SOAP specific things myself to facilitate this communications? I could do that but that will be very time consuming and sometimes error prone too.

Where does Web Services come in picture? Well, Web services is the mechanism that ASP.NET framework provides to make it easy for us to write code to facilitate connectivity between applications. As ASP.NET developer, If I need an application that will be used by many other applications then I can simply decide to write a web service for it and ASP.NET framework will take care of doing the low level SOAP and XML work for us.

The other side of the coin is, if our ASP.NET application wants to use a web service, i.e., an application that is providing me SOAP based interface for communication. So what we are going to do now is write a small Web service to see how we can have our application communication-ready for other applications and secondly, we will try to consume a webservice to understand how we can use other applications from our application.

Creating a Web Service

Let us write a simple module that will provide basic arithmetic operations to other applications. The user of our application will have to provide us 2 numbers and we will perform the requested operation like Addition, Subtraction and Multiplication.

So, the first thing we need to do is to create our web service. We can do this by creating a website of type ASP.NET Web service. This will give us a skeleton to write our web service code in.

[WebService(Namespace = "http://tempuri.org/")]


[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]


public class Service : System.Web.Services.WebService
{

public Service () 

{

        //Uncomment the following line if using designed components

        //InitializeComponent();

  }

 [WebMethod]

public string HelloWorld()

 {

       return "Hello World";

  }


}

The attribute WebService tells that this class contains the code for web service. The namespace is what is used to identify the web service. The WebMethod attribute specifies the methods which our web service is providing.

Let us now go ahead and write code to have our functions in this webservice.

[WebService(Namespace = "http://tempuri.org/")]

[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]




public class Service : System.Web.Services.WebService
{

    public Service ()
    {

        //Uncomment the following line if using designed components

        //InitializeComponent();

    }

    [WebMethod]

    public int Add(int x, int y)

    {

        return x+y;
    }

    [WebMethod]

    public int Subtract(int x, int y)

    {

        return x - y;
    }

    [WebMethod]

    public int Multiply(int x, int y)

    {

        return x * y;
    }

}

We have a very basic web service implemented which can let the user have some basic arithmetic operations. Now to create the WebService binary, we will have to use the following command on Visual Studio Command Prompt.

>CSC /t:library /out:ArithmeticServiceImpl.dll App_code\Service.cs

This will create a DLL file for our web service. This DLL file can be used by any client by using the SOAP protocol. If we need to test our web service for how it works over the SOAP protocol, we can view the service.asmx file in the browser and see what functions our web service is exposing.

We can even test these methods here and see the XML file that contains the service description.

Consuming a WebService

There are three ways we can consume a WebService:

1. Using HTTP-POST method.
2. Using XMLHttp that will use SOAP to call our the service
3. Using WSDL generated proxy class

The HTTP-Post method can be used by calling .asmx file directly from client. We can directly use the method name and the parameter names will be taken from our input fields on form.

<html>

    <body>

        <form action="http://localhost/.../Service.asmx/Multiply"  method="POST">

                <input name="x"></input>

                <input name="y"></input>

                <input type="submit" value="Enter"> </input>

        </form>

    </body>

</html>

When this form get submitted, the web service's method will be called. The second method where we can use the XMLHttp over SOAP to access the webservice is used when we want to use the web service using full capability of SOAP.

The third way of using the web service is by generating a Proxy class for the web service and then using that proxy class. This method is, to me, more type safe and less error prone as once we have the proxy class generated, it can take care of SOAP messages, serialization and ensure that all the problems can be handled at compile time instead of runtime.

To use this service, we need to do "Add Web reference" and add the webservice reference. Alternatively I can also use WSDL.exe, a command line tool, to generate the proxy classes and use them. "Add web Reference" is also using the same WSDL.exe to generate the proxy classes.

Now let us write some code to use the proxy class to perform the operations, the proxy class will then communicate to the web service using SOAP and get back the results to us.

protected void Button1_Click(object sender, EventArgs e)
{

    if (txtX.Text != string.Empty && txtY.Text != string.Empty)
    {

        try

        {

            int x = Convert.ToInt32(txtX.Text);

            int y = Convert.ToInt32(txtY.Text);

            ArithmeticService.Service service = new ArithmeticService.Service();

            Label1.Text = "Sum: " + service.Add(x, y).ToString();

            Label2.Text = "Difference: " + service.Subtract(x, y).ToString();

            Label3.Text = "Multiplication: " + service.Multiply(x, y).ToString();
        }

        catch(Exception)
        {

            throw;

        }
    }

}

Let us run the website to see the results

SQL Interview

ADO: ActiveX Data Objects and ADO.Net are two different ways to access database in Microsoft.

ADO	ADO.Net
ADO is base on COM: Component Object Modelling based.	ADO.Net is based on CLR: Common Language Runtime based.
ADO stores data in binary format.	ADO.Net stores data in XML format i.e. parsing of data.
ADO can’t be integrated with XML because ADO have limited access of XML.	ADO.Net can be integrated with XML as having robust support of XML.
In ADO, data is provided by RecordSet.	In ADO.Net data is provided by DataSet or DataAdapter.
ADO is connection oriented means it requires continuous active connection.	ADO.Net is disconnected, does not need continuous connection.
ADO gives rows as single table view, it scans sequentially the rows using MoveNext method.	ADO.Net gives rows as collections so you can access any record and also can go through a table via loop.
In ADO, You can create only Client side cursor.	In ADO.Net, You can create both Client & Server side cursors.
Using a single connection instance, ADO cannot handle multiple transactions.	Using a single connection instance, ADO.Net can handle multiple transactions.

Drop Down list operations

1) Display a text at its index in drop down list.
ddl_idtype.SelectedIndex = ddl_idtype.Items.IndexOf(ddl_idtype.Items.FindByText("String"));

Top 10 Most Used SQL Query

Create a table: We start by creating an empty table by firing the following query:

1. CREATE TABLE student  
2. (  
3.     id INTEGER PRIMARY KEY,  
4.     name varchar(20),  
5.     address varchar(50),  
6.     age INTEGER  
7. );  

This will create a table called “student” with 0 rows in it. This table will store records of students. It will have student id, student name, student address & student age. Its structure will be like this:

Now we will start taking most used 10 queries one by one.

1. Insert Query:
   To insert the records in a table we use Insert Command. The SQL INSERT INTO Statement is used to add new rows of data to a table in the database.
   
   Syntax:
   INSERT INTO TABLE_NAME (column1, column2, column3,...columnN)] VALUES (value1, value2, value3,...valueN);
   Here, column1, column2,...columnN are the names of the columns in the table into which you want to insert data.
   
   You may not need to specify the column(s) name in the SQL query if you are adding values for all the columns of the table. But make sure the order of the values is in the same order as the columns in the table. The SQL INSERT INTO syntax would be as follows:
   
   Syntax:
   INSERT INTO TABLE_NAME VALUES (value1,value2,value3,...valueN);
   Example:
   Specify the column names in order after the table name in INSERT INTO statement and then the values you want after VALUES keyword.
   
   
   1. INSERT INTO student (id, name, age) VALUES (‘1’, ‘Nitin’, ‘Noida’, 28);  
   After firing this query, our table will look like:
   
   ID Name Address Age
   
     1     Nitin  Noida     26
   
   We can fire more such queries to fill records in our table:
   
   1. Insert into student (id, name, address, age) values (‘2’, 'Amit', ‘New Delhi ‘23’);  
   2. Insert into student (id, name, address, age) values (‘3’, 'Rohit', ‘Bareilly’ ‘27’);  
   
   So the table now becomes:
   
   ID Name Address Age
   
   1    Nitin Noida       26
   2    Amit New Delhi 23
   3    Rohit Bareilly    27
   
2. Select Query: Viewing all records from a table. These results tables are called result-sets.
   
   Syntax: The basic syntax of SELECT statement is as follows:
   
   SELECT column1, column2, columnN FROM table_name;
   Here, column1, column2...are the fields of a table whose values you want to fetch. If you want to fetch all the fields available in the field, then you can use the following syntax:
   
   SELECT * FROM table_name;
   Example:
   1. SELECT * FROM student;  
   The result of this query will be a display of all rows present in the table.
   
   ID Name Address Age
   
   1 Nitin Noida 26
   2 Amit New Delhi 23
   3 Rohit Bareilly 27
   
   We can also use ORDER BY clause in our select statement to arrange the displayed result in a particular order. For example,
   
   SELECT * FROM student ORDER BY age;
   Result is:
   ID Name Address Age
   
   2 Amit New Delhi 23
   1 Nitin Noida 26
   3 Rohit Bareilly 27
   
   The output is arranged in increasing order of age. We can use DESC keyword after the column name in query if we want to arrange the display in decreasing order.
   
3. Viewing only selected records from a table:
   If there are a huge number of rows in a table and we do not want all the records to fill our display screen, then SQL gives us an option to view only selected rows. Count is useful in counting the number of records.
   
   Syntax: SELECT COUNT(1) FROM table_name;
   Example: SELECT COUNT(1) FROM student;
   The output of this query will be:
   ID Name Address Age 
   
     1 Nitin Noida 26
   
   If we fire: 
   SELECT COUNT * FROM student;
   It will return the number of rows our table has. We can also use MAX & MIN function in our query. For example, if we want to retrieve details of a student with maximum age, we can fire:
   
   SELECT id , name , MAX(age) FROM student;
   We will get:
   ID Name Address Age
   3 Rohit Bareilly 27
   
   We can also check sum of a numeric column. 
   
   For example: SELECT sum(age)FROM student;
   
   It will give 76 as output.
   
   Remember, we can use MAX, MIN, SUM functions only with numeric columns. Using these functions with text column will throw an error.
   
4. Deleting records from a table: To delete the selected rows from a table, just fire the following query,
   
   Syntax: DELETE FROM student WHERE [condition];
   
   Example: DELETE FROM student WHERE name = ‘Rohit’;
   This query will delete the entire row, or more than one row, from table ‘student’ where ‘name’ column have value ‘Rohit’.
   In our case, the result of this query will will look like the following table:
   
   ID Name Address Age
   
   1 Nitin Noida 26
   
   2 Amit New Delhi 23
   
5. Changing data in existing records in a table:
   Suppose we want to change the age of a student named ‘Rohit’ in our table. We would fire this query:
   
   Syntax:The basic syntax of UPDATE query with WHERE clause is as follows:
   
   UPDATE table_nameSET column1 = value1, column2 = value2...., columnN = valueNWHERE [condition];
   Example: 
   UPDATE student SET age = 28 WHERE name = ‘Rohit’;
   You might have observed that we are specifying name in ‘’ where values are characters. This is a must.
   
   Now if we fire:
   SELECT * FROM student;
   We will get the following table as output:
   
   ID Name Address Age
   
   1 Nitin Noida 26
   2 Amit New Delhi 23
   3 Rohit Bareilly 28
   
   Be careful while you are firing UPDATE or DELETE queries with the help of the WHERE clause. Suppose in our table ‘student’ there is more than one student with name ‘Rohit’. In this case, age of all students with the name ‘Rohit’ will be updated to 28. That is why it is always preferred to use PRIMARY KEY in WHERE clause while updating or deleting.
   
   We also need to take care of datatypes in a column while we are changing data in it. A numeric column can have only numbers in it while a text column can have text. This means that if we try to put age = ‘Rohit’ in age column using UPDATE statement, SQL will throw an exception. You can learn more about types of errors and exceptions that occur in SQL. 
   
6. Viewing records from a table without knowing exact details:
   In real life, when we interact with database, there are major chances that we do not know any of the column values exactly. For example, if I am a data operator in a company, I may be aware of the fact that there is an employee called Nitin in our Company as I might have heard other managers talking about him. Now I want to see entire records of Nitin but I am not sure how he spells his name. Whether it is ‘Nitin’ OR ‘Netin’. In this case we can use ‘LIKE’ operator provided by SQL.
   
   We will fire the following query:
   SELECT * FROM student WHERE name LIKE ‘n%n’;
   Output of this query will be:
   ID Name Address Age
   
     1 Nitin Noida 26
   
7. Using more than one condition in WHERE clause to retrieve records:
   To understand the requirement of using this parameter, let us first insert two more rows in our table. Try adding two rows in our table ‘student’ with ID as 4 and 5, name as ‘Suchi’ and age as 22 and 24.
   
   Our table now becomes as:
   ID Name Address Age
   
   1 Nitin Noida 26
   2 Amit New Delhi 23
   3 Rohit Bareilly 27
   4 Suchi Lucknow 22
   5 Suchi Patna 24
   
   Now if we fire our query as:
   SELECT * FROM student WHERE name = ‘suchi’;
   Then output will be:
   ID Name Address Age
   
   4 Suchi Lucknow 22
   5 Suchi Patna 24
   
   So now, we have observed that we were unable to fetch a unique record just by using the name value in WHERE clause. Here arises a need to combine more than one condition in WHERE clause which can be easily done using conditional keywords like AND and OR. For example, if we fire:
   
   SELECT * FROM student WHERE name = ‘suchi’ AND age = 24;
   We get the following output:
   ID Name Address Age
   
     5 Suchi Patna 24
   
   You can also combine AND & OR conditions in WHERE clause to refine your search further more. For example, if we fire
   
   SELECT * FROM student WHERE name = ‘suchi’ OR age > 23
   Output will be:
   ID Name Address Age
   
   1 Nitin Noida 26
   3 Rohit Bareilly 27
   4 Suchi Lucknow 22
   5 Suchi Patna 24
   
   You can use different conditions like AND, OR , <, > in a combination or individually in WHERE clause to fetch the desired rows. 
   
8. Viewing only selected columns from a table:
   If we fire a query like:
   
   SELECT name FROM student WHERE age > 25;
   The following output is displayed:
   Name
   
   Nitin 
   Rohit
   
   We can observe that only names of students are printed. Here we got names of only those students whose age is greater than 25 because of a specified condition in WHERE clause.
   
   We can also use more than one column names in SELECT statement separating them with a,
   
   For example:
   SELECT name, address FROM student;
   Gives this as output:
   Name Address
   
   Nitin Noida 
   Amit New Delhi 
   Rohit Bareilly
   Suchi Lucknow
   Suchi Patna
   
   You can also change the sequence of columns to be displayed on your screen. 
   
   For example:
   SELECT age, name FROM student;
   It will give the following output:
   Age Name
   
   26 Nitin 
   23 Amit
   27 Rohit
   22 Suchi
   24 Suchi
   
9. Know the structure of table:
   It happens with me quite often that I create a table in my database and forget what all columns it has and which column is primary key. With the help of a simple query you can know complete details about the structure of the table you created. Different SQL engines have different commands for it. For example, in SQLite3 the command is:
   
   .schema student;
   • Where as in PostgreSQL it is \d student
   • MySQL uses the following command: describe student;
   • Where ‘student’ is our table’s name.
   
10. Checking performance of query:
    This is an advanced query. It’s particularly useful if you need to figure out why a query is so slow.
    
    Just fire the query:
    EXPLAIN QUERY PLAN SELECT * FROM student;
    This query gives the Query Cost of all operations.
    
    You can use EXPLAIN before a SQL statement to obtain breakup of the timings of the various parts of query. It’s useful for digging up the reason behind a slow query.