ASP.NET AJAX Interview Questions

The ASP.NET AJAX Interview Questions contains the most frequently asked questions in ASP.NET AJAX. These lists of questions will gauge your familiarity with the ASP.NET AJAX platform.

What is Ajax?

The term Ajax was coined by Jesse James Garrett and is a short form for "Asynchronous Javascript and XML". Ajax represents a set of commonly used techniques, like HTML/XHTML, CSS, Document Object Model(DOM), XML/XSLT, Javascript and the XMLHttpRequest object, to create RIA's (Rich Internet Applications).

Ajax gives the user, the ability to dynamically and asynchronously interact with a web server, without using a plug-in or without compromising on the user’s ability to interact with the page. This is possible due to an object found in browsers called the XMLHttpRequest object.

What is ASP.NET AJAX?

‘ASP.NET AJAX’ is a terminology coined by Microsoft for ‘their’ implementation of AJAX, which is a set of extensions to ASP.NET. These components allow you to build rich AJAX enabled web applications, which consists of both server side and client side libraries.

Which is the current version of ASP.NET AJAX Control Toolkit?

As of this writing, the toolkit version is Version 1.0.20229 (if you are targeting Framework 2.0, ASP.NET AJAX 1.0 and Visual Studio 2005) and Version 3.0.20229 (if targeting .NET Framework 3.5 and Visual Studio 2008).

What role does the ScriptManager play?

The ScriptManager manages all ASP.NET AJAX resources on a page and renders the links for the ASP.NET AJAX client libraries, which lets you use AJAX functionality like PageMethods, UpdatePanels etc. It creates the PageRequestManager and Application objects, which are prominent in raising events during the client life cycle of an ASP.NET AJAX Web page. It also helps you create proxies to call web services asynchronously.

Can we use multiple ScriptManager on a page?

No. You can use only one ScriptManager on a page.

What is the role of a ScriptManagerProxy?

A page can contain only one ScriptManager control. If you have a Master-Content page scenario in your application and the MasterPage contains a ScriptManager control, then you can use the ScriptManagerProxy control to add scripts to content pages.

Also, if you come across a scenario where only a few pages in your application need to register to a script or a web service, then its best to remove them from the ScriptManager control and add them to individual pages, by using the ScriptManagerProxy control. That is because if you added the scripts using the ScriptManager on the Master Page, then these items will be downloaded on each page that derives from the MasterPage, even if they are not needed, which would lead to a waste of resources.

What are the requirements to run ASP.NET AJAX applications on a server?

You would need to install ‘ASP.NET AJAX Extensions’ on your server. If you are using the ASP.NET AJAX Control toolkit, then you would also need to add the AjaxControlToolkit.dll in the /Bin folder.

Note: ASP.NET AJAX 1.0 was available as a separate downloadable add-on for ASP.NET 2.0. With ASP.NET 3.5, the AJAX components have been integrated into ASP.NET.

Explain the UpdatePanel?

The UpdatePanel enables you to add AJAX functionality to existing ASP.NET applications. It can be used to update content in a page by using Partial-page rendering. By using Partial-page rendering, you can refresh only a selected part of the page instead of refreshing the whole page with a postback.

Can I use ASP.NET AJAX with any other technology apart from ASP.NET?

To answer this question, check out this example of using ASP.NET AJAX with PHP, to demonstrate running ASP.NET AJAX outside of ASP.NET. Client-Side ASP.NET AJAX framework can be used with PHP and Coldfusion.

How can you cancel an Asynchronous postback?

Yes you can. Read my article over here.

Difference between Server-Side AJAX framework and Client-side AJAX framework?

ASP.NET AJAX contains both a server-side Ajax framework and a client-side Ajax framework. The server-side framework provides developers with an easy way to implement Ajax functionality, without having to possess much knowledge of JavaScript. The framework includes server controls and components and the drag and drop functionality. This framework is usually preferred when you need to quickly ajaxify an asp.net application. The disadvantage is that you still need a round trip to the server to perform a client-side action.

The Client-Side Framework allows you to build web applications with rich user-interactivity as that of a desktop application. It contains a set of JavaScript libraries, which is independent from ASP.NET. The library is getting rich in functionality with every new build released.

 How can you debug ASP.NET AJAX applications?

Explain about two tools useful for debugging: Fiddler for IE and Firebug for Mozilla.

Can you nest UpdatePanel within each other?

Yes, you can do that. You would want to nest update panels to basically have more control over the Page Refresh.

How can you to add JavaScript to a page when performing an asynchronous postback?

Use the ScriptManager class. This class contains several methods like the RegisterStartupScript(), RegisterClientScriptBlock(), RegisterClientScriptInclude(), RegisterArrayDeclaration(),RegisterClientScriptResource(), RegisterExpandoAttribute(), RegisterOnSubmitStatement() which helps to add javascript while performing an asynchronous postback.

Explain differences between the page execution lifecycle of an ASP.NET page and an ASP.NET AJAX page?

In an asynchronous model, all the server side events occur, as they do in a synchronous model. The Microsoft AJAX Library also raises client side events. However when the page is rendered, asynchronous postback renders only the contents of the update panel, where as in a synchronous postback, the entire page is recreated and sent back to the browser.

Is the ASP.NET AJAX Control Toolkit(AjaxControlToolkit.dll) installed in the Global Assembly Cache?

No. You must copy the AjaxControlToolkit.dll assembly to the /Bin folder in your application.

 Those were some frequently asked questions you should have knowledge about. In one of the coming articles, we will cover some more ASP.NET AJAX FAQ’s which were not covered in this article. I hope this article was useful and I thank you for viewing it.

General .NET Interview Questions

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).

Compare C# and VB.NET

A detailed comparison can be found over here.

What is a base class and derived class?

A class is a template for creating an object. The class from which other classes derive fundamental functionality is called a base class. For e.g. If Class Y derives from Class X, then Class X is a base class.

The class which derives functionality from a base class is called a derived class. If Class Y derives from Class X, then Class Y is a derived class.

What is an extender class?

An extender class allows you to extend the functionality of an existing control. It is used in Windows forms applications to add properties to controls.

A demonstration of extender classes can be found over here.

What is inheritance?

Inheritance represents the relationship between two classes where one type derives functionality from a second type and then extends it by adding new methods, properties, events, fields and constants.

C# support two types of inheritance:

·         Implementation inheritance

·         Interface inheritance

What is implementation and interface inheritance?

When a class (type) is derived from another class(type) such that it inherits all the members of the base type it is Implementation Inheritance.

When a type (class or a struct) inherits only the signatures of the functions from another type it is Interface Inheritance.

In general Classes can be derived from another class, hence support Implementation inheritance. At the same time Classes can also be derived from one or more interfaces. Hence they support Interface inheritance.

Source: Exforsys.

What is inheritance hierarchy?

The class which derives functionality from a base class is called a derived class. A derived class can also act as a base class for another class. Thus it is possible to create a tree-like structure that illustrates the relationship between all related classes. This structure is known as the inheritance hierarchy.

How do you prevent a class from being inherited?

In VB.NET you use the NotInheritable modifier to prevent programmers from using the class as a base class. In C#, use the sealed keyword.

When should you use inheritance?

Read this.

Define Overriding?

Overriding is a concept where a method in a derived class uses the same name, return type, and arguments as a method in its base class. In other words, if the derived class contains its own implementation of the method rather than using the method in the base class, the process is called overriding.

Can you use multiple inheritance in .NET?

.NET supports only single inheritance. However the purpose is accomplished using multiple interfaces.

Why don’t we have multiple inheritance in .NET?

There are several reasons for this. In simple words, the efforts are more, benefits are less. Different languages have different implementation requirements of multiple inheritance. So in order to implement multiple inheritance, we need to study the implementation aspects of all the languages that are CLR compliant and then implement a common methodology of implementing it. This is too much of efforts. Moreover multiple interface inheritance very much covers the benefits that multiple inheritance has.

What is an Interface?

An interface is a standard or contract that contains only the signatures of methods or events. The implementation is done in the class that inherits from this interface. Interfaces are primarily used to set a common standard or contract.

When should you use abstract class vs interface or What is the difference between an abstract class and interface?

I would suggest you to read this. There is a good comparison given over here.

What are events and delegates?

An event is a message sent by a control to notify the occurrence of an action. However it is not known which object receives the event. For this reason, .NET provides a special type called Delegate which acts as an intermediary between the sender object and receiver object.

What is business logic?

It is the functionality which handles the exchange of information between database and a user interface.

What is a component?

Component is a group of logically related classes and methods. A component is a class that implements the IComponent interface or uses a class that implements IComponent interface.

What is a control?

A control is a component that provides user-interface (UI) capabilities.

What are the differences between a control and a component?

The differences can be studied over here.

What are design patterns?

Design patterns are common solutions to common design problems.

What is a connection pool?

A connection pool is a ‘collection of connections’ which are shared between the clients requesting one. Once the connection is closed, it returns back to the pool. This allows the connections to be reused.

What is a flat file?

A flat file is the name given to text, which can be read or written only sequentially.

What are functional and non-functional requirements?

Functional requirements defines the behavior of a system whereas non-functional requirements specify how the system should behave; in other words they specify the quality requirements and judge the behavior of a system.

E.g.

Functional - Display a chart which shows the maximum number of products sold in a region.

Non-functional – The data presented in the chart must be updated every 5 minutes.

What is the global assembly cache (GAC)?

GAC is a machine-wide cache of assemblies that allows .NET applications to share libraries. GAC solves some of the problems associated with dll’s (DLL Hell).

What is a stack? What is a heap? Give the differences between the two?

Stack is a place in the memory where value types are stored. Heap is a place in the memory where the reference types are stored.

Check this link for the differences.

What is instrumentation?

It is the ability to monitor an application so that information about the application’s progress, performance and status can be captured and reported.

What is code review?

The process of  examining the source code generally through a peer, to verify it against best practices.

What is logging?

Logging is the process of persisting information about the status of an application.

What are mock-ups?

Mock-ups are a set of designs in the form of screens, diagrams, snapshots etc., that helps verify the design and acquire feedback about the application’s requirements and use cases, at an early stage of the design process.

What is a Form?

A form is a representation of any window displayed in your application. Form can be used to create standard, borderless, floating, modal windows.

What is a multiple-document interface(MDI)?

A user interface container that enables a user to work with more than one document at a time. E.g. Microsoft Excel.

What is a single-document interface (SDI) ?

A user interface that is created to manage graphical user interfaces and controls into single windows. E.g. Microsoft Word

What is BLOB ?

A BLOB (binary large object) is a large item such as an image or an exe  represented in binary form.

What is ClickOnce?

ClickOnce is a new deployment technology that allows you to create and publish self-updating applications that can be installed and run with minimal user interaction.

What is object role modeling (ORM) ?

It is a logical model for designing and querying database models. There are various ORM tools in the market like CaseTalk, Microsoft Visio for Enterprise Architects, Infagon etc.

What is a private assembly?

A private assembly is local to the installation directory of an application and is used only by that application.

What is a shared assembly?

A shared assembly is kept in the global assembly cache (GAC) and can be used by one or more applications on a machine.

What is the difference between user and custom controls?

User controls are easier to create whereas custom controls require extra effort.

User controls are used when the layout is static whereas custom controls are used in dynamic layouts.

A user control cannot be added to the toolbox whereas a custom control can be.

A separate copy of a user control is required in every application that uses it whereas since custom controls are stored in the GAC, only a single copy can be used by all applications.

Where do custom controls reside?

In the global assembly cache (GAC).

What is a third-party control ?

A third-party control is one that is not created by the owners of a project. They are usually used to save time and resources and reuse the functionality developed by others (third-party).

What is a binary formatter?

Binary formatter is used to serialize and deserialize an object in binary format.

What is Boxing/Unboxing?

Boxing is used to convert value types to object.

E.g. int x = 1;

object obj = x ;

Unboxing is used to convert the object back to the value type.

E.g. int y = (int)obj;

Boxing/unboxing is quiet an expensive operation.

What is a COM Callable Wrapper (CCW)?

CCW is a wrapper created by the common language runtime(CLR) that enables COM components to access .NET objects.

What is a Runtime Callable Wrapper (RCW)?

RCW is a wrapper created by the common language runtime(CLR) to enable .NET components to call COM components.

What is a digital signature?

A digital signature is an electronic signature used to verify/gurantee the identity of the individual who is sending the message.

What is garbage collection?

Garbage collection is the process of managing the allocation and release of memory in your applications. Read this article for more information.

What is globalization?

Globalization is the process of customizing applications that support multiple cultures and regions.

What is localization?

Localization is the process of customizing applications that support a given culture and regions.

What is MIME?

The definition of MIME or Multipurpose Internet Mail Extensions as stated in MSDN is “MIME is a standard that can be used to include content of various types in a single message. MIME extends the Simple Mail Transfer Protocol (SMTP) format of mail messages to include multiple content, both textual and non-textual. Parts of the message may be images, audio, or text in different character sets.

ASP.NET 2.0 Interview Questions

What is ASP.NET?

Microsoft ASP.NET is a server side technology that enables programmers to build dynamic Web sites, web applications, and XML Web services. It is a part of the .NET based environment and is built on the Common Language Runtime (CLR) . So programmers can write ASP.NET code using any .NET compatible language.

What are the differences between ASP.NET 1.1 and ASP.NET 2.0?

A comparison chart containing the differences between ASP.NET 1.1 and ASP.NET 2.0 can be found over 

Which is the latest version of ASP.NET? What were the previous versions released?

The latest version of ASP.NET is 2.0. There have been 3 versions of ASP.NET released as of date. They are as follows :

ASP.NET 1.0 – Released on January 16, 2002.

ASP.NET 1.1 – Released on April 24, 2003.

ASP.NET 2.0 – Released on November 7, 2005.

Additionally, ASP.NET 3.5 is tentatively to be released by the end of the 2007.

Explain the Event Life cycle of ASP.NET 2.0?

The events occur in the following sequence. Its best to turn on tracing(<% @Page Trace=”true”%>) and track the flow of events :

PreInit – This event represents the entry point of the page life cycle. If you need to change the Master page or theme programmatically, then this would be the event to do so. Dynamic controls are created in this event.

Init – Each control in the control collection is initialized.

Init Complete* - Page is initialized and the process is completed.

PreLoad* - This event is called before the loading of the page is completed.

Load – This event is raised for the Page and then all child controls. The controls properties and view state can be accessed at this stage. This event indicates that the controls have been fully loaded.

LoadComplete* - This event signals indicates that the page has been loaded in the memory. It also marks the beginning of the rendering stage.

PreRender – If you need to make any final updates to the contents of the controls or the page, then use this event. It first fires for the page and then for all the controls.

PreRenderComplete* - Is called to explicitly state that the PreRender phase is completed.

SaveStateComplete* - In this event, the current state of the control is completely saved to the ViewState.

Unload – This event is typically used for closing files and database connections. At times, it is also used for logging some wrap-up tasks.

The events marked with * have been introduced in ASP.NET 2.0.

You have created an ASP.NET Application. How will you run it?

With ASP.NET 2.0, Visual Studio comes with an inbuilt ASP.NET Development Server to test your pages. It functions as a local Web server. The only limitation is that remote machines cannot access pages running on this local server. The second option is to deploy a Web application to a computer running IIS version 5 or 6 or 7.

Explain the AutoPostBack feature in ASP.NET?

AutoPostBack allows a control to automatically postback when an event is fired. For eg: If we have a Button control and want the event to be posted to the server for processing, we can set AutoPostBack = True on the button.

How do you disable AutoPostBack?

Hence the AutoPostBack can be disabled on an ASP.NET page by disabling AutoPostBack on all the controls of a page. AutoPostBack is caused by a control on the page.

What are the different code models available in ASP.NET 2.0?

There are 2 code models available in ASP.NET 2.0. One is the single-file page and the other one is the code behind page.

Which base class does the web form inherit from?

Page class in the System.Web.UI namespace.

Which are the new special folders that are introduced in ASP.NET 2.0?

There are seven new folders introduced in ASP.NET 2.0 :

\App_Browsers folder – Holds browser definitions(.brower) files which identify the browser and their capabilities.

\App_Code folder – Contains source code (.cs, .vb) files which are automatically compiled when placed in this folder. Additionally placing web service files generates a proxy class(out of .wsdl) and a typed dataset (out of .xsd).

\App_Data folder – Contains data store files like .mdf (Sql Express files), .mdb, XML files etc. This folder also stores the local db to maintain membership and role information.

\App_GlobalResources folder – Contains assembly resource files (.resx) which when placed in this folder are compiled automatically. In earlier versions, we were required to manually use the resgen.exe tool to compile resource files. These files can be accessed globally in the application.

\App_LocalResources folder – Contains assembly resource files (.resx) which can be used by a specific page or control.

\App_Themes folder – This folder contains .css and .skin files that define the appearance of web pages and controls.

 \App_WebReferences folder – Replaces the previously used Web References folder. This folder contains the .disco, .wsdl, .xsd files that get generated when accessing remote web services.

Explain the ViewState in ASP.NET?

Http is a stateless protocol. Hence the state of controls is not saved between postbacks. Viewstate is the means of storing the state of server side controls between postbacks. The information is stored in HTML hidden fields. In other words, it is a snapshot of the contents of a page.

You can disable viewstate by a control by setting the EnableViewState property to false.

What does the EnableViewState property signify?

EnableViewState saves the state of an object in a page between postbacks. Objects are saved in a Base64 encoded string. If you do not need to store the page, turn it off as it adds to the page size.

There is an excellent article by Peter Bromberg to understand Viewstate in depth.

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.

This list has been taken from here.

Explain the Validation Controls used in ASP.NET 2.0?

Validation controls allows you to validate a control against a set of rules. There are 6 different validation controls used in ASP.NET 2.0.

RequiredFieldValidator – Checks if the control is not empty when the form is submitted.

CompareValidator – Compares the value of one control to another using a comparison operator (equal, less than, greater than etc).

RangeValidator – Checks whether a value falls within a given range of number, date or string.

RegularExpressionValidator – Confirms that the value of a control matches a pattern defined by a regular expression. Eg: Email validation.

CustomValidator – Calls your own custom validation logic to perform validations that cannot be handled by the built in validators.

ValidationSummary – Show a summary of errors raised by each control on the page on a specific spot or in a message box.

How do you indentify that the page is post back?

By checking the IsPostBack property. If IsPostBack is True, the page has been posted back.

What are Master Pages?

Master pages is a template that is used to create web pages with a consistent layout throughout your application. Master Pages contains content placeholders to hold page specific content. When a page is requested, the contents of a Master page are merged with the content page, thereby giving a consistent layout.

How is a Master Page different from an ASP.NET page?

The MasterPage has a @Master top directive and contains ContentPlaceHolder server controls. It is quiet similar to an ASP.NET page.

How do you attach an exisiting page to a Master page?

By using the MasterPageFile attribute in the @Page directive and removing some markup.

How do you set the title of an ASP.NET page that is attached to a Master Page?

By using the Title property of the @Page directive in the content page. Eg:

<@Page MasterPageFile="Sample.master" Title="I hold content" %>

What is a nested master page? How do you create them?

A Nested master page is a master page associated with another master page. To create a nested master page, set the MasterPageFile attribute of the @Master directive to the name of the .master file of the base master page.

What are Themes?

Themes are a collection of CSS files, .skin files, and images. They are text based style definitions and are very similar to CSS, in that they provide a common look and feel throughout the website.

What are skins?

A theme contains one or more skin files. A skin is simply a text file with a .skin extension and contains definition of styles applied to server controls in an ASP.NET page. For eg:

<asp:button runat="server" BackColor="blue" BorderColor="Gray" Font-Bold ="true" ForeColor="white"/>

Defines a skin that will be applied to all buttons throughout to give it a consistent look and feel.

What is the difference between Skins and Css files?

Css is applied to HTML controls whereas skins are applied to server controls.

What is a User Control?

User controls are reusable controls, similar to web pages. They cannot be accessed directly.

Explain briefly the steps in creating a user control?

·         Create a file with .ascx extension and place the @Control directive at top of the page.

·         Included the user control in a Web Forms page using a @Register directive

What is a Custom Control?

Custom controls are compiled components that run on the server and that encapsulate user-interface and other related functionality into reusable packages. They can include all the design-time features of standard ASP.NET server controls, including full support for Visual Studio design features such as the Properties window, the visual designer, and the Toolbox.

What are the differences between user and custom controls?

User controls are easier to create in comparison to custom controls, however user controls can be less convenient to use in advanced scenarios.

User controls have limited support for consumers who use a visual design tool whereas custom controls have full visual design tool support for consumers.

A separate copy of the user control is required in each application that uses it whereas only a single copy of the custom control is required, in the global assembly cache, which makes maintenance easier.

A user control cannot be added to the Toolbox in Visual Studio whereas custom controls can be added to the Toolbox in Visual Studio.

User controls are good for static layout whereas custom controls are good for dynamic layout.

Where do you store your connection string information?

The connection string can be stored in configuration files (web.config). 

What is the difference between ‘Web.config’ and ‘Machine.config’?

Web.config files are used to apply configuration settings to a particular web application whereas machine.config file is used to apply configuration settings for all the websites on a web server.

Web.config files are located in the application's root directory or inside a folder situated in a lower hierarchy. The machine.config is located in the Windows directory Microsoft.Net\Framework\Version\CONFIG.

There can be multiple web.config files in an application nested at different hierarchies. However there can be only one machine.config file on a web server.

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().

What is a webservice?

Web Services are applications delivered as a service on the Web. Web services allow for programmatic access of business logic over the Web. Web services typically rely on XML-based protocols, messages, and interface descriptions for communication and access. Web services are designed to be used by other programs or applications rather than directly by end user. Programs invoking a Web service are called clients. SOAP over HTTP is the most commonly used protocol for invoking Web services.

What is XHTML? Are ASP.NET Pages compliant with XHTML?

In simple words, XHTML is a stricter and cleaner version of HTML. XHTML stands for EXtensible Hypertext Markup Language and is a W3C Recommendation.

Yes, ASP.NET 2.0 Pages are XHTML compliant. However the freedom has been given to the user to include the appropriate document type declaration.

Can I deploy the application without deploying the source code on the server?

Yes. You can obfuscate your code by using a new precompilation process called ‘precompilation for deployment’. You can use the aspnet_compiler.exe to precompile a site. This process builds each page in your web application into a single application DLL and some placeholder files. These files can then be deployed to the server.

You can also accomplish the same task using Visual Studio 2005 by using the Build->Publish menu.

Does ViewState affect performance? What is the ideal size of a ViewState? How can you compress a viewstate?

Viewstate stores the state of controls in HTML hidden fields. At times, this information can grow in size. This does affect the overall responsiveness of the page, thereby affecting performance. The ideal size of a viewstate should be not more than 25-30% of the page size.

Viewstate can be compressed to almost 50% of its size. .NET also provides the GZipStream or DeflateStream to compress viewstate. Another option is explained by Scott Hanselmann over .

How can you detect if a viewstate has been tampered?

By setting the EnableViewStateMac to true in the @Page directive. This attribute checks the encoded and encrypted viewstate for tampering.

Can I use different programming languages in the same application?

Yes. Each page can be written with a different programming language in the same application. You can create a few pages in C# and a few in VB.NET.

Can the App_Code folder contain source code files in different programming languages?

No. All source code files kept in the root App_Code folder must be in the same programming language.

Update: However, you can create two subfolders inside the App_Code and then add both C# and VB.NET in the respective subfolders.  You also have to add configuration settings in the web.config for this to work.

How do you secure your connection string information?

By using the Protected Configuration feature.

How do you secure your configuration files to be accessed remotely by unauthorized users?

ASP.NET configures IIS to deny access to any user that requests access to the Machine.config or Web.config files.

How can I configure ASP.NET applications that are running on a remote machine?

You can use the Web Site Administration Tool to configure remote websites.

How many web.config files can I have in an application?

You can keep multiple web.config files in an application. You can place a Web.config file inside a folder or wherever you need (apart from some exceptions) to override the configuration settings that are inherited from a configuration file located at a higher level in the hierarchy.

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.

What is the difference between Response.Write and Response.Output.Write?

As quoted by Scott Hanselman, the short answer is that the latter gives you String.Format-style output and the former doesn't. 

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.

Can you change a Master Page dynamically at runtime? How?

Yes. To change a master page, set the MasterPageFile property to point to the .master page during the PreInit page event.

How do you apply Themes to an entire application?

By specifying the theme in the web.config file.

Eg: <configuration>

<system.web>

<pages theme=”BlueMoon” />

</system.web>

</configuration>

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.

Your client complains that he has a large form that collects user input. He wants to break the form into sections, keeping the information in the forms related. Which control will you use?

The ASP.NET Wizard Control.

To learn more about this control, visit this link.

Do webservices support data reader?

No. However it does support a dataset.

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, WMI, or COM interfaces to configure IIS programmatically.

How does Application Pools work in IIS 6.0?

As explained under the IIS documentation, when you run IIS 6.0 in worker process isolation mode, you can separate different Web applications and Web sites into groups known as application pools. An application pool is a group of one or more URLs that are served by a worker process or set of worker processes. Any Web directory or virtual directory can be assigned to an application pool.

Every application within an application pool shares the same worker process. Because each worker process operates as a separate instance of the worker process executable, W3wp.exe, the worker process that services one application pool is separated from the worker process that services another. Each separate worker process provides a process boundary so that when an application is assigned to one application pool, problems in other application pools do not affect the application. This ensures that if a worker process fails, it does not affect the applications running in other application pools.

Use multiple application pools when you want to help ensure that applications and Web sites are confidential and secure. For example, an enterprise organization might place its human resources Web site and its finance Web site on the same server, but in different application pools. Likewise, an ISP that hosts Web sites and applications for competing companies might run each companys Web services on the same server, but in different application pools. Using different application pools to isolate applications helps prevent one customer from accessing, changing, or using confidential information from another customers site.

In HTTP.sys, an application pool is represented by a request queue, from which the user-mode worker processes that service an application pool collect the requests. Each pool can manage requests for one or more unique Web applications, which you assign to the application pool based on their URLs. Application pools, then, are essentially worker process configurations that service groups of namespaces.

Multiple application pools can operate at the same time. An application, as defined by its URL, can only be served by one application pool at any time. While one application pool is servicing a request, you cannot route the request to another application pool. However, you can assign applications to another application pool while the server is running.