ASP.NET Interview Questions

ASP.NET Interview Questions

This is a list of questions I have gathered and created over a period of time from my experience, many of which I felt where incomplete or simply wrong.  I have finally taken the time to go through each question and correct them to the best of my ability.  However, please feel free to post feedback to challenge, improve, or suggest new questions.  I want to thank those of you that have contributed quality questions and corrections thus far.

There are some questions in this list that I do not consider to be good questions for an interview.  However, they do exist on other lists available on the Internet so I felt compelled to keep them here for easy access.

1. Describe the role of inetinfo.exe, aspnet_isapi.dll andaspnet_wp.exe in the page loading process.
   inetinfo.exe is theMicrosoft IIS server running, handling ASP.NET requests among other things.When an ASP.NET request is received (usually a file with .aspx extension), the ISAPI filter aspnet_isapi.dll takes care of it by passing the request tothe actual worker process aspnet_wp.exe.
    
2. What’s the difference between Response.Write() andResponse.Output.Write()?Response.Output.Write() allows you to write formatted output.
    
3. What methods are fired during the page load?Init() - when the page is instantiated
   Load() - when the page is loaded into server memory
   PreRender() - the brief moment before the page is displayed to the user as HTML
   Unload() - when page finishes loading.
    
4. When during the page processing cycle is ViewState available?
   After the Init() and before the Page_Load(), or OnLoad() for a control.
    
5. What namespace does the Web page belong in the .NET Framework class hierarchy?System.Web.UI.Page
    
6. Where do you store the information about the user’s locale?System.Web.UI.Page.Culture
    
7. What’s the difference between Codebehind="MyCode.aspx.cs" andSrc="MyCode.aspx.cs"?CodeBehind is relevant to Visual Studio.NET only.
    
8. What’s a bubbled event?When you have a complex control, like DataGrid, writing an event processing routine for each object (cell, button, row, etc.) is quite tedious. The controls can bubble up their eventhandlers, allowing the main DataGrid event handler to take care of its constituents.
    
9. Suppose you want a certain ASP.NET function executed on MouseOver for a certain button.  Where do you add an event handler?Add an OnMouseOver attribute to the button.  Example: btnSubmit.Attributes.Add("onmouseover","someClientCodeHere();");
    
10. What data types do the RangeValidator control support?Integer, String, and Date.
     
11. Explain the differences between Server-side and Client-side code?Server-side code executes on the server.  Client-side code executes in the client's browser.
     
12. What type of code (server or client) is found in a Code-Behind class?The answer is server-side code since code-behind is executed on the server.  However, during the code-behind's execution on the server, it can render client-side code such as JavaScript to be processed in the clients browser.  But just to be clear, code-behind executes on the server, thus making it server-side code.
     
13. Should user input data validation occur server-side or client-side?  Why?All user input data validation should occur on the server at a minimum.  Additionally, client-side validation can be performed where deemed appropriate and feasable to provide a richer, more responsive experience for the user.
     
14. What is the difference between Server.Transfer and Response.Redirect?  Why would I choose one over the other?Server.Transfer transfers page processing from one page directly to the next page without making a round-trip back to the client's browser.  This provides a faster response with a little less overhead on the server.  Server.Transfer does not update the clients url history list or current url.  Response.Redirect is used to redirect the user's browser to another page or site.  This performas a trip back to the client where the client's browser is redirected to the new page.  The user's browser history list is updated to reflect the new address.
     
15. Can you explain the difference between an ADO.NET Dataset and an ADO Recordset?Valid answers are:
    ·  A DataSet can represent an entire relational database in memory, complete with tables, relations, and views.·  A DataSet is designed to work without any continuing connection to the original data source.·  Data in a DataSet is bulk-loaded, rather than being loaded on demand.·  There's no concept of cursor types in a DataSet.·  DataSets have no current record pointer You can use For Each loops to move through the data.·  You can store many edits in a DataSet, and write them to the original data source in a single operation.·  Though the DataSet is universal, other objects in ADO.NET come in different versions for different data sources.
     
16. What is the Global.asax used for?The Global.asax (including the Global.asax.cs file) is used to implement application and session level events.
     
17. What are the Application_Start and Session_Start subroutines used for?This is where you can set the specific variables for the Application and Session objects.
     
18. Can you explain what inheritance is and an example of when you might use it?When you want to inherit (use the functionality of) another class.  Example: With a base class named Employee, a Manager class could be derived from the Employee base class.
     
19. Whats an assembly?Assemblies are the building blocks of the .NET framework. Overview of assemblies from MSDN
     
20. Describe the difference between inline and code behind.Inline code written along side the html in a page. Code-behind is code written in a separate file and referenced by the .aspx page.
     
21. Explain what a diffgram is, and a good use for one?The DiffGram is one of the two XML formats that you can use to render DataSet object contents to XML.  A good use is reading database data to an XML file to be sent to a Web Service.
     
22. Whats MSIL, and why should my developers need an appreciation of it if at all?MSIL is the Microsoft Intermediate Language. All .NET compatible languages will get converted to MSIL.  MSIL also allows the .NET Framework to JIT compile the assembly on the installed computer.
     
23. Which method do you invoke on the DataAdapter control to load your generated dataset with data?The Fill() method.
     
24. Can you edit data in the Repeater control?No, it just reads the information from its data source.
     
25. Which template must you provide, in order to display data in a Repeater control?ItemTemplate.
     
26. How can you provide an alternating color scheme in a Repeater control?Use the AlternatingItemTemplate.
     
27. What property must you set, and what method must you call in your code, in order to bind the data from a data source to the Repeater control?You must set the DataSource property and call the DataBind method.
     
28. What base class do all Web Forms inherit from?The Page class.
     
29. Name two properties common in every validation control?ControlToValidate property and Text property.
     
30. Which property on a Combo Box do you set with a column name, prior to setting the DataSource, to display data in the combo box?DataTextField property.
     
31. Which control would you use if you needed to make sure the values in two different controls matched?CompareValidator control.
     
32. How many classes can a single .NET DLL contain?It can contain many classes.
     

Web Service Questions

1. What is the transport protocol you use to call a Web service?SOAP (Simple Object Access Protocol) is the preferred protocol.
    
2. True or False: A Web service can only be written in .NET?False
    
3. What does WSDL stand for?Web Services Description Language.
    
4. Where on the Internet would you look for Web services?http://www.uddi.org
    
5. True or False: To test a Web service you must create a Windows application or Web application to consume this service?False, the web service comes with a test page and it provides HTTP-GET method to test.
    

State Management Questions

1. What is ViewState?ViewState allows the state of objects (serializable) to be stored in a hidden field on the page.  ViewState is transported to the client and back to the server, and is not stored on the server or any other external source.  ViewState is used the retain the state of server-side objects between postabacks.
    
2. What is the lifespan for items stored in ViewState?Item stored in ViewState exist for the life of the current page.  This includes postbacks (to the same page).
    
3. What does the "EnableViewState" property do?  Why would I want it on or off?It allows the page to save the users input on a form across postbacks.  It saves the server-side values for a given control into ViewState, which is stored as a hidden value on the page before sending the page to the clients browser.  When the page is posted back to the server the server control is recreated with the state stored in viewstate.
    
4. What are the different types of Session state management options available with ASP.NET?
   ASP.NET provides In-Process and Out-of-Process state management.  In-Process stores the session in memory on the web server.  This requires the a "sticky-server" (or no load-balancing) so that the user is always reconnected to the same web server.  Out-of-Process Session state management stores data in an external data source.  The external data source may be either a SQL Server or a State Server service.  Out-of-Process state management requires that all objects stored in session are serializable.

3-Tire Architecture Overview

Introduction

As a developer, the .NET framework and Visual Studio present many choices for choosing the right architecture, from placing the data access code directly in the UI through datasets and data source controls, to creating a data access layer that talks to the database, all the way to creating an n-tier architecture approach that consists of multiple layers, and use data-transfer objects to pass data back and forth.
If you’ve ever wondered why you should use layers and what the benefits are, this article is for you. This article delves into the use of layers and how they can benefit any application.

What is a Layer?

A layer is a reusable portion of code that performs a specific function. In the .NET environment, a layer is usually setup as a project that represents this specific function. This specific layer is in charge of working with other layers to perform some specific goal. In an application where the presentation layer needs to extract information from a backend database, the presentation would utilize a series of layers to retrieve the data, rather than having the database calls embedded directly within itself. Let’s briefly look at the latter situation first.

Two-Tier Architecture

When the .NET 2.0 framework became available to the world, there were some neat features that allowed the developer to connect the framework’s GUI controls directly to the database. This approach is very handy when rapidly developing applications. However, it’s not always favorable to embed all of the business logic and data access code directly in the web site, for several reasons:

• Putting all of the code in the web site (business logic and data access) can make the application harder to maintain and understand.
• Reusing database queries in the presentation layer often isn’t done, because of the typical data source control setup in the ASP.NET framework.
• Relying on the data source controls can make debugging more difficult, often due to vague error messages.

So in looking for an alternative, we can separate the data access code and business logic into separate “layers”, which we’ll discuss next.

The Data Layer

The key component to most applications is the data. The data has to be served to the presentation layer somehow. The data layer is a separate component (often setup as a separate single or group of projects in a .NET solution), whose sole purpose is to serve up the data from the database and return it to the caller. Through this approach, data can be logically reused, meaning that a portion of an application reusing the same query can make a call to one data layer method, instead of embedding the query multiple times. This is generally more maintainable.
But the question is how is the data returned? Multiple frameworks employ different techniques, and below is a summary:

• ADO.NET – Built into the .NET framework, ADO.NET contains a mechanism to query data out of the database and return it to the caller in a connected or disconnected fashion. This is the most common approach to working with data, because it’s already readily available. See more at: http://en.wikipedia.org/wiki/ADO.NET.
• Table Adapters/Strongly-Typed Datasets – Strongly-typed datasets and table adapters provide a similar means to querying the data through ADO.NET, but add strong-typing features, meaning custom objects are generated for you to work with. See more here.
• Enterprise Library – Enterprise library Data Access Application Block provides a flexible way to connect to databases of multiple types, without having to know anything about that database, through an abstract approach. See more at: http://msdn2.microsoft.com/en-us/magazine/cc188705.aspx (read part one first).
• LINQ-to-SQL – LINQ to SQL is an ORM tool that uses a DataContext object as the central point to query data from the database. See more here. (read parts one through eight first).
• Auto-Generated Code – Tools like CodeSmith Studio automatically generate the code for you based upon a database schema. Simply writing a script to output the code you want to use and the backend is generated in a short amount of time. See more at: http://community.codesmithtools.c om/blogs/tutorials/archive/2006/02/13/nettiers.aspx.

Most (if not all) options above take advantage of the CRUD (create, read, update, or delete) operations that databases support, so all of that is available as shown above. There are plenty of resources online to help you get started. To see an overview of some of the options, please read this.

Business Layer

Though a web site could talk to the data access layer directly, it usually goes through another layer called the business layer. The business layer is vital in that it validates the input conditions before calling a method from the data layer. This ensures the data input is correct before proceeding, and can often ensure that the outputs are correct as well. This validation of input is called business rules, meaning the rules that the business layer uses to make “judgments” about the data.
However, business rules don’t only apply to data validation; these rules apply to any calculations or any other action that takes place in the business layer. Normally, it’s best to put as much logic as possible in the business layer, which makes this logic reusable across applications.
One of the best reasons for reusing logic is that applications that start off small usually grow in functionality. For instance, a company begins to develop a web site, and as they realize their business needs, they later decide to add a smart client application and windows service to supplement the web site. The business layer helps move logic to a central layer for “maximum reusability.”

Presentation Layer

The ASP.NET web site or windows forms application (the UI for the project) is called the presentation layer. The presentation layer is the most important layer simply because it’s the one that everyone sees and uses. Even with a well structured business and data layer, if the presentation layer is designed poorly, this gives the users a poor view of the system.
It’s best to remove as much business logic out of the UI and into the business layer. This usually involves more code, but in my mind, the excess time (which ranges from minimal to moderate, depending on the size of the application) pays off in the end.
However, a well-architected system leaves another question: how do you display it in an ASP.NET or windows application? This can be more of a problem in ASP.NET, as the controls are more limited to the type of inputs they can receive. If you use certain architectures, like passing datasets from the data to the presentation layer, this isn’t as much of a challenge; however, the challenge can come with business objects that support drill-through business object references.

Why Separating Logic Is Useful

You may wonder why it is important to move as much logic outside the presentation layer and into the business layer. The biggest reason is reuse: logic placed in a business layer increases the reusability of an application. As applications grow, applications often grow into other realms. Applications may start out as a web application, but some of the functionality may later be moved to a smart client application. Portions of an application may be split between a web site and a web or windows service that runs on a server. In addition, keeping logic helps aid in developing a good design (sometimes code can get sloppier in the UI).
However, there are some caveats to this: it takes a little longer to develop applications when most of the logic resides in the business layer. The reason is this often involves creating several sets of objects (data layer and access code, plus business objects) rather than embedding it in the application. The extra time that it takes to do this can be a turnoff for some managers and project leads, especially because it often requires you to be knowledgeable about object-oriented programming, more than most people are comfortable with.
Although embedding code in the UI is easier, in most cases I don’t believe it’s the best approach. A layered approach is often a better approach because it pays dividends down the road. This is because as more and more code is developed, the following happens:

• Code is copied and pasted frequently, or code is reused in classes that could easily be moved to a business layer.
• Code that is very similar is often copied and pasted with slight modification, making duplication harder to track down.
• It’s harder to maintain; even though applications with business objects are larger applications, they usually are structured better.
• Code is harder to unit test, if unit testing is available at all. Web applications and windows forms projects are hard to use unit testing with.

A good architecture is often harder to implement, but is easier to maintain because it often reduces the volume of code. This means that hours spent supporting an application are reduced.

Distributed Applications

Using a separation of layers can aid in development of distributed applications. Because the code is broken up into layers, a layer that facilitates the use of remoting or web services can be added to the project, with a minimal amount of work.

Development Techniques

When developing a business object architecture, it’s good to know about the many design patterns that are out there. There are many websites, blogs, and books related to the subject of design patterns. One of the more well-known books on the subject is titled “Design Patterns,” whom the authors are often referred to as the Gang of Four.
Another useful development technique is called Refactoring, or improving the quality of your code by making small changes to the way it works. This involves moving code into a method, or moving a method from one object to another, in a systematic, logical way. Martin Fowler has written a great book on this subject, called “Refactoring, Improving the Design of Existing Code.” There are plenty of books on the subject; this one is the source that helped me to understand refactoring the most.
There are also tools on the market that can help you refactor in a faster way. One of those tools is Resharper by Jet Brains, which looks for a lot of code patterns and refactors them in a way that is useful. Some of the other refactoring tools that I heard about are Refactor Pro by DevExpress (free for VB.NET and ASP.NET), Visual Assist X by Whole Tomato Software, and Just Code by OmniCore.

Conclusion

This article reviewed the use of layers in an application, and discussed the fundamentals of their use. It also discussed the purpose of each layer, why using layers is important, and some other techniques useful for developing applications.