ASP.NET Questions For Experts and Developers, Part-II

ASP.NET Questions For Experts, Part-II

1. Whats an assembly?

Assemblies are the building blocks of .NET Framework applications; they form the fundamental unit of deployment, version control, reuse, activation scoping, and security permissions. An assembly is a collection of types and resources that are built to work together and form a logical unit of functionality. An assembly provides the common language runtime with the information it needs to be aware of type implementations. To the runtime, a type does not exist outside the
context of an assembly.

2. Describe the difference between inline and code behind - which is best in a loosely coupled
   solution?

ASP.NET supports two modes of page development: Page logic code that is written inside <script runat=server> blocks within an .aspx file and dynamically compiled the first time the page is requested on the server. Page logic code that is written within an external class that is compiled prior to deployment on a server and linked "behind" the .aspx file at run time.

3. Explain what a diffgram is, and a good use for one?
   A DiffGram is an XML format that is used to identify current and original versions of data elements. The DataSet uses the DiffGram format to load and persist its contents, and to serialize its contents for transport across a network connection. When a DataSet is written as a DiffGram, it populates the DiffGram with all the necessary information to accurately recreate the contents, though not the schema, of the DataSet, including column values from both the Original and Current row versions, row error information, and row order.
4. Where would you use an iHTTPModule, and what are the limitations of anyapproach you might take in implementing one?
   One of ASP.NET’s most useful features is the extensibility of the HTTP pipeline, the path that data takes between client and server. You can use them to extend your ASP.NET applications by adding pre- and post-processing to each HTTP request coming into your application. For example, if you wanted custom authentication facilities for your application, the best technique would be to intercept the request when it comes in and process the request in a custom HTTP module.
5. What are the disadvantages of viewstate/what are the benefits?
   
   
6. Describe session handling in a webfarm, how does it work and what are the limits?
7. How would you get ASP.NET running in Apache web servers - why would you even do this?
8. Whats MSIL, and why should my developers need an appreciation of it if at all?
9. In what order do the events of an ASPX page execute. As a developer is it important to understand these events

 Every Page object (which your .aspx page is) has nine events, most of which you will not have to
worry about in your day to day dealings with ASP.NET. The three that you will deal with the most are: Page_Init, Page_Load, Page_PreRender.

10. Which method do you invoke on the DataAdapter control to load your generated dataset with data?

System.Data.Common.DataAdapter.Fill(System.Data.DataSet);
If my DataAdapter is sqlDataAdapter and my DataSet is dsUsers then it is called
this way:

sqlDataAdapter.Fill(dsUsers);

11. ata in the Repeater control?
12. Which template must you provide, in order to display data in a Repeater control? ItemTemplate
13. How can you provide an alternating color scheme in a Repeater control?
    
    AlternatingItemTemplate Like the ItemTemplate element, but rendered for every other
    
    row (alternating items) in the Repeater control. You can specify a different appearance
    
    for the AlternatingItemTemplate element by setting its style properties.
    
    
14. What property must you set, and what method must you call in your code, in order to bind the data from some data source to the Repeater control?
    You must set the DataMember property which Gets or sets the specific
    table in the DataSource to bind to the control and the DataBind method
    to bind data from a source to a server control. This method is commonly
    used after retrieving a data set through a database query.

15. What base class do all Web Forms inherit from?

              System.Web.UI.Page

16. What method do you use to explicitly kill a user’s session?
    
    The Abandon method destroys all the objects stored in a Session object
    and releases their resources.
    
    If you do not call the Abandon method explicitly, the server destroys
    these objects when the session times out.
    
    
    
    Syntax: Session.Abandon
17. How do you turn off cookies for one page in your site?
    
    Use the Cookie.Discard Property which Gets or sets the discard flag set by the server. When true, this property instructs the client application not to save the Cookie on the user’s hard disk when a session ends.
18. Which two properties are on every validation control?
    ControlToValidate & ErrorMessage properties
19. What tags do you need to add within the asp:datagrid tags to bind columns manually?
20. How do you create a permanent cookie?

Setting the Expires property to MinValue means that the Cookie never expires.

21. What tag do you use to add a hyperlink column to the DataGrid?
    
    
22. What is the standard you use to wrap up a call to a Web service?
23. Which method do you use to redirect the user to another page without performing a round trip to the client?

Server.transfer()

24. What is the transport protocol you use to call a Web service?

SOAP. Transport Protocols: It is essential for the acceptance of Web Services that they are based on established Internet infrastructure. This in fact imposes the usage of of the HTTP, SMTP and FTP protocols based on the TCP/IP family of transports. Messaging Protocol: The format of messages exchanged between Web Services clients and Web Services should be vendor neutral and should not carry details about the technology used to implement the service. Also, the message format should allow for extensions and different bindings to specific transport protocols. SOAP and ebXML Transport are specifications which fulfill these requirements. We expect that the W3C XML Protocol Working Group defines a successor standard.

25. True or False: A Web service can only be written in .NET. False.
26. What does WSDL stand for?

Web Services Description Language

27. What property do you have to set to tell the grid which page to go to when using the Pager object?
28. Where on the Internet would you look for Web services?
    UDDI repositaries like uddi.microsoft.com, IBM UDDI node, UDDI Registries in Google
    Directory, enthusiast sites like XMethods.net.
29. What tags do you need to add within the asp:datagrid tags to bind columns manually? Column tag and an ASP:databound tag.
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?
    
    
31. How is a property designated as read-only?

In VB.NET:

<![if !supportLists]>32.<![endif]>Public ReadOnly Property PropertyName As ReturnType

<![if !supportLists]>33.<![endif]> Get ‘Your Property Implementation goes in here

<![if !supportLists]>34.<![endif]> End Get

End Property

in
C#

public returntype PropertyName

{

get{

//property
implementation goes here

}

// Do not write
the set implementation

}

35. Which control would you use if you needed to make sure the values in two different controls matched?

Use the CompareValidator control to compare the values of 2 different controls.

36. True or False: To test a Web service you must create a windows application or Web application to consume this service?

False.

How many classes can a single .NET DLL contain?
Unlimited

ASP.NET Interview Questions For Experts, Part- I

ASP.NET questions For Experts, Part- I

1. Explain the differences between Server-side and Client-side code?

Server side scripting means that all the script will be executed by the server and interpreted as
needed. ASP doesn’t have some of the functionality like sockets, uploading, etc. For these you have to make a custom components usually in VB or VC++. Client side scripting means that the script will be executed immediately in the browser such as form field validation, clock, email validation, etc. Client side scripting is usually done in VBScript or JavaScript. Download time, browser compatibility, and visible code - since JavaScript and VBScript code is included in the HTML page, then anyone can see the code by viewing the page source. Also a possible security hazards for the client computer.

2. What type of code (server or client) is found in a Code-Behind class? C#
3. Should validation (did the user enter a real date) occur server-side or client-side? Why? Client-side validation because there is no need to request a server side date when you could
   obtain a date from the client machine.
4. What does the "EnableViewState" property do? Why would I want it on or off? Enable ViewState turns on the automatic state management feature that enables server controls to
   re-populate their values on a round trip without requiring you to write any code. This feature is not free however, since the state of a control is passed to and from the server in a hidden form field. You should be aware of when ViewState is helping you and when it is not. For example, if you are binding a control to data on every round trip (as in the datagrid example in tip #4), then you do not need the control to maintain it’s view state, since you will wipe out any re-populated data
   in any case. ViewState is enabled for all server controls by default. To disable it, set the EnableViewState property of the control to false.
5. What is the difference between Server.Transfer and Response.Redirect? Why would I choose one over the other?
   Server.Transfer() : client is shown as it is on the requesting page only, but the all the content is of the requested page. Data can be persist accros the pages using Context.Item collection, which is one of the best way to transfer data from one page to another keeping the page state alive. Response.Dedirect() :client know the physical loation (page name and query string as well). Context.Items loses the persisitance when nevigate to destination page. In earlier versions of IIS, if we wanted to send a user to a new Web page, the only option we had was Response.Redirect. While this method does accomplish our goal, it has several important drawbacks. The biggest problem is that this method causes each page to be treated as a separate transaction. Besides making it difficult to maintain your transactional integrity, Response.Redirect introduces some additional headaches. First, it prevents good encapsulation of code. Second, you lose access to all of the properties in the Request object. Sure, there are workarounds, but they’re difficult. Finally, Response.Redirect necessitates a round trip to the client, which, on high-volume sites, causes scalability problems. As you might suspect, Server.Transfer fixes all of these problems. It does this by performing the transfer on the server without requiring a roundtrip to the client.
6. Can you give an example of when it would be appropriate to use a web service as opposed to a non-serviced .NET component?
   When to Use Web Services:
• Communicating through a Firewall -When building a distributed application with 100s/1000s of users spread over multiple locations, there is always the problem of communicating between client and server because of firewalls and proxy servers. Exposing your middle tier components as Web Services and invoking the directly from a Windows UI
  is a very valid option.
• Application Integration- When integrating applications written in various languages and running on disparate systems. Or even applications running on the same platform that have
  been written by separate vendors.
• Business-to-Business Integration - This is an enabler for B2B intergtation which allows one to expose vital business processes to authorized supplier and customers. An example would be exposing electronic ordering and invoicing, allowing customers to send you
  purchase orders and suppliers to send you invoices electronically.
• Software Reuse This takes place at multiple
  levels. Code Reuse at the Source code level or binary componet-based resuse. The limiting factor here is that you can reuse the code but not the data behind it. Webservice overcome this limitation. A scenario could be when you are building an app that aggregates the functionality of serveral other Applicatons. Each of these functions could be performed by individual apps, but there is value in perhaps combining the the multiple apps to present a unifiend view in a Portal or Intranet.
• When not to use Web
  Services: Single machine Applicatons When the apps are running on the same machine and need to communicate with each other use a native
  API. You also have the options of using component technologies such as COM or .NET Componets as there is very little overhead.
• Homogeneous Applications on a LAN

If you have Win32 or Winforms apps that want to communicate to their server counterpart. It is much more efficient to use DCOM in the case of Win32 apps and .NET Remoting in the case of .NET Apps.

7. Let’s say I have an existing application written using Visual Studio (VBInterDevand this application utilizes WindowsCOM+ transaction services. How would you approach
   migrating this application to .NET?
8. Can you explain the difference between an ADO.NET Dataset and an ADO Recordset?

In ADO, the in-memory representation of data is the recordset. In ADO.NET, it is the dataset.
There are important differences between them.

• A recordset looks like a single table. If a recordset is to contain data from multiple database tables, it must use a JOIN query, which assembles the data from the various database tables into a single result table. In contrast, a dataset is a collection of one or more tables. The tables within a dataset are called data tables; specifically, they are DataTable objects. If a
  dataset contains data from multiple database tables, it will typically contain multiple DataTable objects. That is, each DataTable object typically corresponds to a single database table or view. In this way, a dataset can mimic the structure of the underlying database. A dataset usually also contains relationships. A relationship within a dataset is analogous to a foreign-key relationship in a database —that is, it associates rows of the tables with each other. For example, if a dataset contains a table about investors and another table about each investor’s stock purchases, it could also contain a relationship connecting each row of the investor table with the corresponding rows of the purchase table. Because the dataset can hold multiple, separate tables and maintain information about relationships between them, it can hold much richer data structures than a recordset, including self-relating tables and tables with many-to-many relationships.
• In ADO you scan sequentially through the rows of the recordset using the ADO MoveNext method. In ADO.NET, rows are represented as collections, so you can loop through a table as you would through any collection, or access particular rows via ordinal or primary key index. DataRelation objects maintain information about master and detail records and provide a method that allows you to get records related to the one you are working with. For example, starting from the row of the Investor table for "Nate Sun," you can navigate to the set of rows of the Purchase table describing his purchases. A cursor is a database element that controls record navigation, the ability to update data, and the visibility of
  changes made to the database by other users. ADO.NET does not have an inherent cursor object, but instead includes data classes that provide the functionality of a traditional cursor. For example, the functionality of a forward-only, read-only cursor is available in the
  ADO.NET DataReader object. For more information about cursor functionality, see Data Access Technologies.
• Minimized Open Connections: In ADO.NET you open connections only long enough to perform a database operation, such as a Select or Update. You can read rows into a dataset and then work with them without staying connected to the data source. In ADO the recordset can provide disconnected access, but ADO is designed primarily for connected access. There is one significant difference between disconnected processing in ADO and ADO.NET. In ADO you communicate with the database by making calls to an OLE DB provider. In ADO.NET you communicate with the database through a data adapter (an OleDbDataAdapter, SqlDataAdapter, OdbcDataAdapter, or OracleDataAdapter object), which makes calls to an OLE DB provider or the APIs provided by the underlying data source. The important difference is that in ADO.NET the data adapter allows you to control
  how the changes to the dataset are transmitted to the database — by optimizing for performance, performing data validation checks, or adding any other extra processing. Data adapters, data connections, data commands, and data readers are the components that make up a .NET Framework data provider. Microsoft and third-party providers can make available other .NET Framework data providers that can be integrated into Visual Studio.
• Sharing Data Between Applications. Transmitting an ADO.NET dataset between applications is much easier than transmitting an ADO disconnected recordset. To transmit an ADO disconnected recordset from one component to another, you use COM marshalling. To transmit data in ADO.NET, you use a dataset, which can transmit an XML stream.
• Richer data types.COM marshalling provides a limited set of data types — those defined by the COM standard. Because the transmission of datasets in ADO.NET is based on an XML format, there is no restriction on data types. Thus, the components sharing the dataset can use whatever rich set of data types they would ordinarily use.
• Performance. Transmitting a large ADO recordset or a large ADO.NET dataset can consume network resources; as the amount of data grows, the stress placed on the network also rises. Both ADO and ADO.NET let you minimize which data is transmitted. But ADO.NET offers another performance advantage, in that ADO.NET does not require data-type conversions. ADO, which requires COM marshalling to transmit records sets among components, does require that ADO data types be converted to COM data types.
• Penetrating Firewalls.A firewall can interfere with two components trying to transmit disconnected ADO recordsets. Remember, firewalls are typically configured to allow HTML
  text to pass, but to prevent system-level requests (such as COM marshalling) from passing.
8. Can you give an example of what might be best suited to place in the Application_Start and
   Session_Start subroutines?
   The Application_Start event is guaranteed to occur only once throughout the lifetime of the application. It’s a good place to initialize global variables. For example, you might want to retrieve a list of products from a database table and place the list in application state or the Cache object. SessionStateModule exposes both Session_Start and Session_End events.
9. If I’m developing an application that must accomodate multiple security levels though secure login and my ASP.NET web appplication is spanned across three web-servers (using round-robbin load balancing) what would be the best approach to maintain login-in state for the users?
10. What are ASP.NET Web Forms? How is this technology different than what is available though ASP? Web Forms are the heart and
    soul of ASP.NET.
    Web Forms are the User Interface (UI) elements that give your Web
    applications their look and feel. Web Forms are similar to Windows Forms
    in that they provide properties, methods, and events for the controls
    that are placed onto them. However, these UI elements render themselves
    in the appropriate markup language required by the request, e.g. HTML.
    If you use Microsoft Visual Studio .NET, you will also get the familiar
    drag-and-drop interface used to create your UI for your Web application.
    
    
11. How does VB.NET/C# achieve polymorphism?
    By using Abstract classes/functions.
12. Can you explain what inheritance is and an example of when you might use it?

 Inheritance is a fundamental feature of an object oriented system and it is simply the ability to
inherit data and functionality from a parent object. Rather than developing new objects from scratch, new code can be based on the work of other programmers, adding only new features that are needed.

How would you implement inheritance using VB.NET/C#?
When we set out to implement a class using inheritance, we must first start with an existing class from which we will derive our new subclass. This existing class, or base class, may be part of the .NET system class library framework, it may be part of some other application or .NET assembly,
or we may create it as part of our existing application. Once we have a base class, we can then implement one or more subclasses based on that base class. Each of our subclasses will automatically have all of the methods, properties, and events of that base class ? including the
implementation behind each method, property, and event. Our subclass can add new methods, properties, and events of its own - extending the original interface with new functionality. Additionally, a subclass can replace the methods and properties of the base class with its own new
implementation - effectively overriding the original behavior and replacing it with new behaviors. Essentially inheritance is a way of merging functionality from an existing class into our new subclass. Inheritance also defines rules for how these methods, properties, and events can be merged.