What is an interface and what is an abstract class?

26. What is an interface and what is an abstract class?

In an interface, all methods must be abstract (must not be defined). In an abstract class, some methods can be defined. In an interface, no accessibility modifiers are allowed, whereas it is allowed in abstract classes.

27. Session state vs. View state:

In some cases, using view state is not feasible. The alternative for view state is session state. Session state is employed under the following situations:

1.     Large amounts of data - View state tends to increase the size of both the HTML page sent to the browser and the size of form posted back. Hence session state is used.

2.     Secure data - Though the view state data is encoded and may be encrypted, it is better and secure if no sensitive data is sent to the client. Thus, session state is a more secure option.

3.     Problems in serializing of objects into view state - View state is efficient for a small set of data. Other types like DataSet are slower and can generate a very large view state.

28. Can two different programming languages be mixed in a single ASPX file?

ASP.NET’s built-in parsers are used to remove code from ASPX files and create temporary files. Each parser understands only one language. Therefore mixing of languages in a single ASPX file is not possible.

29. Is it possible to see the code that ASP.NET generates from an ASPX file?

By enabling debugging using a <%@ Page Debug="true" %> directive in the ASPX file or a <compilation debug="true"> statement in Web.config, the generated code can be viewed. The code is stored in a CS or VB file (usually in the \%SystemRoot%\Microsoft.NET\Framework\v1.0.nnnn\Temporary ASP.NET Files).

30. Can a custom .NET data type be used in a Web form?

This can be achieved by placing the DLL containing the custom data type in the application root's bin directory and ASP.NET will automatically load the DLL when the type is referenced.

31. List the event handlers that can be included in Global.asax?

1. Application starts and end event handlers

2. Session start and end event handlers

3. Per-request event handlers

4. Non-deterministic event handlers

32. Can the view state be protected from tampering?

This can be achieved by including an @ Page directive with an EnableViewStateMac="true" attribute in each ASPX file that has to be protected. Another way is to include the <pages enableViewStateMac="true" /> statement in the Web.config file.

33. Can the view state be encrypted?

The view state can be encrypted by setting EnableViewStateMac to true and either modifying the <machineKey> element in Machine.config to <machineKey validation="3DES” /> or by adding the above statement to Web.config.

38. When during the page processing cycle is ViewState available?

The view state is available after the Init() and before the Render() methods are called during Page load.

39. Do Web controls support Cascading Style Sheets?

All Web controls inherit a property named CssClass from the base class System.Web.UI.WebControls.WebControl which can be used to control the properties of the web control.

40. What namespaces are imported by default in ASPX files?

The following namespaces are imported by default. Other namespaces must be imported manually using @ Import directives.

1.     System

2.     System.Collections

3.     System.Collections.Specialized

4.     System.Configuration

5.     System.Text

6.     System.Text.RegularExpressions

7.     System.Web

8.     System.Web.Caching

9.     System.Web.Security

10. System.Web.SessionState

11. System.Web.UI

12. System.Web.UI.HtmlControls

13. System.Web.UI.WebControls

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