ASP. NET Interview Questions

ASP. NET Interview Questions

Describe the role of inetinfo.exe, aspnet_isapi.dll andaspnet_wp.exe in the page loading process.

inetinfo.exe is the Microsoft 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 to the actual worker process aspnet_wp.exe.

What’s the difference between Response. Write() and Response. Output. Write()?

Response.Output.Write() allows you to write formatted output.

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.

When during the page processing cycle is View State available?

After the Init() and before the Page_Load(), or OnLoad() for a control.

What namespace does the Web page belong in the .NET Framework class hierarchy?

System.Web.UI.Page

Where do you store the information about the user’s locale?

System.Web.UI.Page.Culture

What’s the difference between Codebehind="MyCode.aspx.cs" and Src="MyCode.aspx.cs"?

Code Behind is relevant to Visual Studio.NET only.

What’s a bubbled event?

When you have a complex control, like Data Grid, writing an event processing routine for each object (cell, button, row, etc.) is quite tedious. The controls can bubble up their event handlers, allowing the main Data Grid event handler to take care of its constituents.

Suppose you want a certain ASP. NET function executed on Mouse Over for a certain button. Where do you add an event handler?

Add an OnMouseOver attribute to the button.
Example: btnSubmit.Attributes.Add("onmouseover","someClientCodeHere();");

What data types do the RangeValidator control support?

Integer, String, and Date.

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.

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.

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 feasible to provide a richer, more responsive experience for the user.

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 performs 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.

Can you explain the difference between an ADO. NET Dataset and an ADO Record set?

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.

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.

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.

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.

Whats an assembly?

Assemblies are the building blocks of the .NET framework. Overview of assemblies from MSDN

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.

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.

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.

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

The Fill() method.

Can you edit data in the Repeater control?

No, it just reads the information from its data source.

Which template must you provide, in order to display data in a Repeater control?

ItemTemplate.

How can you provide an alternating color scheme in a Repeater control?

Use the AlternatingItemTemplate.

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.

What base class do all Web Forms inherit from?

The Page class.

Name two properties common in every validation control?

ControlToValidate property and Text property.

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

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

CompareValidator control.

How many classes can a single .NET DLL contain?

It can contain many classes.

True or False: A Web service can only be written in .NET?

False

What does WSDL stand for?

Web Services Description Language

Where on the Internet would you look for Web services?

http://www.uddi.org

Which property on a Combo Box do you set with a column name, prior to setting the Data Source, to display data in the combo box?

DataTextField property

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.

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

SOAP (Simple Object Access Protocol) is the preferred protocol.

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


What is View State?

View State allows the state of objects (serializable) to be stored in a hidden field on the page. View State is transported to the client and back to the server, and is not stored on the server or any other external source. View State is used the retain the state of server-side objects between postabacks.

What is the lifespan for items stored in View State?

Item stored in View State exist for the life of the current page. This includes post backs (to the same page).

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 post backs. It saves the server-side values for a given control into View State, 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 view state.

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.

Explain the code behind wors and contrast that using the inline style.

Different types of HTML,Web and server controls (also how Server control validation controls work)

Difference btn user and server controls

Server controls are built-in. User controls are created by the developer to allow for the reuse of controls that need specific functionality.

How server form post-back works (perhaps ask about view state as well).

By default all pages in .NET post back to themselves. The view state keeps the users input updated on the page.

Can the action attribute of a server-side

tag be set to a value and if not how can you possibly pass data from a form page to a subsequent page.

No, You have to use Server. Transfer to pass the data to another page.

What is the role of global.asax.

Store global information about the application

How would ASP and ASP. NET apps run at the same time on the same server?

What are good ADO. NET object's) to replace the ADO Record set object.

What is view state and use of it?

The current property settings of an ASP. NET page and those of any ASP. NET server controls contained within the page. ASP. NET can detect when a form is requested for the first time versus when the form is posted (sent to the server), which allows you to program accordingly.

What are user controls and custom controls?

Custom controls: A control authored by a user or a third-party software vendor that does not belong to the .NET Framework class library. This is a generic term that includes user controls. A custom server control is used in Web Forms (ASP. NET pages). A custom client control is used in Windows Forms applications.

User Controls: In ASP. NET: A user-authored server control that enables an ASP. NET page to be re-used as a server control. An ASP. NET user control is authored declaratively and persisted as a text file with an .ascx extension. The ASP. NET page framework compiles a user control on the fly to a class that derives from the System.Web.UI.UserControl class.


What are the validation controls?

A set of server controls included with ASP. NET that test user input in HTML and Web server controls for programmer-defined requirements. Validation controls perform input checking in server code. If the user is working with a browser that supports DHTML, the validation controls can also perform validation using client script

What's the difference between Response. Write() and Response.Output.Write()?

The latter one allows you to write formatted output

Where does the Web page belong in the .NET Framework class hierarchy?

System.Web.UI.Page

Where do you store the information about the user's locale?

System.Web.UI.Page.Culture

What's the difference between Code behind="MyCode.aspx.cs" and Src="MyCode.aspx.cs"? Code Behind is relevant to Visual Studio.NET only.

What's a bubbled event?

When you have a complex control, likeDataGrid, writing an event processing routine for each object (cell, button, row, etc.) is quite tedious. The controls can bubble up their event handlers, allowing the main Data Grid event handler to take care of its constituents. Suppose you want a certain ASP. NET function executed on Mouse Over over a certain button.

Where do you add an event handler?

It's the Attributes property, the Add function inside that property. e.g. btnSubmit.Attributes.Add("onMouseOver","some Client Code();")

What data type does the RangeValidator control support?

Integer, String and Date.

Describe the difference between a Thread and a Process?

Thread - is used to execute more than one program at a time.

process - executes single program

What is a Windows Service and how does its lifecycle differ from a “standard” EXE?

Windows Service applications are long-running applications that are ideal for use in server environments. The applications do not have a user interface or produce any visual output; it is instead used by other programs or the system to perform operations. Any user messages are typically written to the Windows Event Log. Services can be automatically started when the computer is booted. This makes services ideal for use on a server or whenever you need long-running functionality that does not interfere with other users who are working on the same computer. They do not require a logged in user in order to execute and can run under the context of any user including the system. Windows Services are controlled through the Service Control Manager where they can be stopped, paused, and started as needed.

How does the lifecycle of Windows services differ from Standard EXE?

Windows services lifecycle is managed by “Service Control Manager” which is responsible for starting and stopping the service and the applications do not have a user interface or produce any visual output, but “Standard executable” doesn’t require Control Manager and is directly related to the visual output

What is the difference between a.Equals(b) and a == b?

a == b is used to compare the references of two objects

a.Equals(b) is used to compare two objects

What is the maximum amount of memory any single process on Windows can address? Is this different than the maximum virtual memory for the system? How would this affect a system design?

What is the difference between an EXE and a DLL?

An EXE can run independently, whereas DLL will run within an EXE. DLL is an in-process file and EXE is an out-process file

What is strong-typing versus weak-typing? Which is preferred? Why?

Strong type is checking the types of variables as soon as possible, usually at compile time. While weak typing is delaying checking the types of the system as late as possible, usually to run-time. Which is preferred depends on what you want. For scripts & quick stuff you’ll usually want weak typing, because you want to write as much less (is this a correct way to use Ensligh?) code as possible. In big programs, strong typing can reduce errors at compile time.

What’s wrong with a line like this? DateTime.Parse(myString)

the result returned by this function is not assigned to anything, should be something like
varx = DateTime.Parse(myString)

What are PDBs? Where must they be located for debugging to work?

A program database (PDB) file holds debugging and project state information that allows incremental linking of a Debug configuration of your program.

The linker creates project.PDB, which contains debug information for the project’s EXE file. The project.PDB contains full debug information, including function prototypes, not just the type information found in VCx0.PDB. Both PDB files allow incremental updates.

They should be located at bin\Debug directory

To debug precompiled components such as business objects and code-behind modules, you need to generate debug symbols. To do this, compile the components with the debug flags by using either Visual Studio .NET or a command line compiler such as Csc.exe (for Microsoft Visual C# .NET) or Vbc.exe (for Microsoft Visual Visual Basic .NET).

Using Visual Studio .NET1. Open the ASP. NET Web Application project in Visual Studio .NET.
2. Right-click the project in the Solution Explorer and click Properties.
3. In the Properties dialog box, click the Configuration Properties folder.
4. In the left pane, select Build.
5. Set Generate Debugging Information to true.
6. Close the Properties dialog box.
7. Right-click the project and click Build to compile the project and generate symbols (.pdb files).
What is cyclomatic complexity and why is it important?

Cyclomatic complexity is a computer science metric (measurement) developed by Thomas McCabe used to generally measure the complexity of a program. It directly measures the number of linearly independent paths through a program’s source code.

The concept, although not the method, is somewhat similiar to that of general text complexity measured by the Flesch-Kincaid Readability Test.

Cyclomatic complexity is computed using a graph that describes the control flow of the program. The nodes of the graph correspond to the commands of a program. A directed edge connects two nodes, if the second command might be executed immediately after the first command. By definition,

CC = E - N + P

where
CC = cyclomatic complexity
E = the number of edges of the graph
N = the number of nodes of the graph
P = the number of connected components.

Write a standard lock() plus double check to create a critical section around a variable access.


What is FullTrust? Do GAC’ed assemblies have FullTrust?

Your code is allowed to do anything in the framework, meaning that all (.Net) permissions are granted. The GAC has FullTrust because it’s on the local HD, and that has FullTrust by default, you can change that using caspol


What benefit does your code receive if you decorate it with attributes demanding specific Security permissions?

What does this do? gacutil /l | find /i “about”

This command is used to install strong typed assembly in GAC

What does this do? sn -t foo.dll

What ports must be open for DCOM over a firewall? What is the purpose of Port 135?

Contrast OOP and SOA. What are tenets of each

Service Oriented Architecture. In SOA you create an abstract layer that your applications use to access various “services” and can aggregate the services. These services could be databases, web services, message queues or other sources. The Service Layer provides a way to access these services that the applications do not need to know how the access is done. For example, to get a full customer record, I might need to get data from a SGL Server database, a web service and a message queue. The Service layer hides this from the calling application. All the application knows is that it asked for a full customer record. It doesn’t know what system or systems it came from or how it was retrieved.


How does the XmlSerializer work? What ACL permissions does a process using it require?

XmlSerializer requires write permission to the system’s TEMP directory.

Why is catch(Exception) almost always a bad idea?


Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies some design flaws in the project.

What is the difference between Debug.Write and Trace.Write? When should each be used?

The Debug.Write call won’t be compiled when the DEBUG symbol is not defined (when doing a release build). Trace.Write calls will be compiled. Debug.Write is for information you want only in debug builds, Trace.Write is for when you want it in release build as well. And in any case, you should use something like log4net because that is both faster and better

What is the difference between a Debug and Release build? Is there a significant speed difference? Why or why not?

Debug build contain debug symbols and can be debugged while release build doesn’t contain debug symbols, doesn’t have [Contional(”DEBUG”)] methods calls compiled, can’t be debugged (easily, that is), less checking, etc. There should be a speed difference, because of disabling debug methods, reducing code size etc but that is not a guarantee (at least not a significant one)

Does JITting occur per-assembly or per-method? How does this affect the working set?

Contrast the use of an abstract base class against an interface?

In the interface all methods must be abstract, in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes

In the context of a comparison, what is object identity versus object equivalence?

How would one do a deep copy in .NET?

System.Array.CopyTo() - Deep copies an Array

Explain current thinking around IClonable.

IClonable interface is used to clone objects like constructor copy in c++

What is boxing?

Boxing is an implicit conversion of a value type to the type object
int i = 123; // A value type
Object box = i // Boxing
Unboxing is an explicit conversion from the type object to a value type
int i = 123; // A value type
object box = i; // Boxing
int j = (int)box; // Unboxing
Convertion of value type to ref type

Is string a value type or a reference type?

string is actually ref Type but some difference with other ref object
Value type - bool, byte, chat, decimal, double, enum , float, int, long, sbyte, short,strut, uint, ulong, ushort
Value types are stored in the Stack
Reference type - class, delegate, interface, object, string
Reference types are stored in the Heap