Thursday, July 17, 2008

Microsoft .NET Faq's

.NET Framework:
.NET framework is an environment that facilitates Object Oriented Programming Model for multiple languages. It wraps Operating System and insulates Software Development from many Operating System specific tasks such as file handling, memory allocation & management.
It has two main components CLR (Common Language Runtime) and .Net BCL (Base Class Libraries).

As you can see in Figure, the .NET Framework sits on top of the operating system, which can be a few different flavors of Windows and consists of a number of components. .NET is essentially a system application that runs on Windows.

The most important component of the Framework is something called the CLR. The CLR activates objects, performs security checks on them, lays them out in memory, executes them, and garbage-collects them. The CLR supports all languages that can be represented in the Common Intermediate Language (CIL). A conceptual difference between the two infrastructures is that Java code runs on multiple platforms with a JVM, whereas .NET code runs only on the Windows platforms with the CLR (at the time of this writing).

An assembly is the basic unit of deployment and versioning, consisting of a manifest, a set of one or more modules, and an optional set of resources.

Metadata is machine -readable information about a resource, or "data about data." Such information might include details on content, format, size, or other characteristics of a data source. In .NET, metadata includes type definitions, version information, external assembly references, and other standardized information.

In order for two components, systems, or objects to interoperate with one another, at least one must know something about the other. In COM, this "something" is an interface specification, which is implemented by a component provider and used by its consumers.

In .NET, metadata is a common mechanism or dialect that the .NET runtime, compilers, and tools can all use. Microsoft .NET uses metadata to describe all types that are used and exposed by a particular .NET assembly. Metadata includes descriptions of an assembly and modules, classes, interfaces, methods, properties, fields, events, global methods, and so forth.

.NET assemblies are deployable units and manifests are the metadata that describes the assemblies.

IL Code:
An assembly contains the IL code that the CLR executes at runtime. The IL code typically uses types defined within the same assembly.

There are four types of assemblies in .NET:
Static assemblies: These are the .NET PE files that you create at compile time. You can create static assemblies using your favorite compiler: csc, cl, or vbc.
Dynamic assemblies: These are PE-formatted, in-memory assemblies that you dynamically create at runtime using the classes in the System.Reflection.Emit namespace.
Private assemblies: These are static assemblies used by a specific application.
Public or shared assemblies: These are static assemblies that must have a unique shared name and can be used by any application.

Side-by-Side Execution:
The CLR allows any versions of the same-shared DLL (shared assembly) to execute at the same time, on the same system, and even in the same process. This concept is known as side-by-side execution.

Manifests: Assembly Metadata
An assembly manifest is metadata that describes everything about the assembly, including its identity, a list of files belonging to the assembly, references to external assemblies, exported types, exported resources, and permission requests. In short, it describes all the details that are required for component plug-and-play. Since an assembly contains all these details, there's no need for storing this type of information in the registry, as in the COM world.

An assembly can be a single-module assembly or a multi-module assembly. In a single-module assembly, everything in a build is clumped into one EXE or DLL, an example of which is the hello.exe application that we developed earlier. This is easy to create because a compiler takes care of creating the single -module assembly for you.

A multi-module assembly is one that contains many modules and resource files. To create it you have to use the Assembly Linker (al.exe) that is provided by the .NET SDK. This tool takes one or more IL or resource files and spits out a file with an assembly manifest.

Any .NET language may be converted into IL, so .NET supports multiple languages and perhaps multiple platforms in the future (as long as the target platforms have a CLR).

Interfaces support exactly the same concept as a C++ abstract base class (ABC) with only pure virtual functions. An ABC is a class that declares one or more pure virtual functions and thus cannot be instantiated. If you know COM or Java, interfaces in .NET are conceptually equivalent to a COM or Java interface. You specify them, but you don't implement them. A class that derives from your interface must implement your interface. An interface may contain methods, properties, indexers, and events. In .NET, a class can derive from multiple interfaces.

The Common Language Specification (CLS):
The CLS specifies a series of basic rules that are required for language integration.

CLR Execution:
The JIT compilers convert IL to native code so that it can execute on the target operating system. The compiled, native code lies in memory until the process shuts down and until the garbage collector clears off all references and memory associated with the process.

You can treat each .NET assembly as a component that you can plug into another component or application, without the need for source code, since all the metadata for the component is stored inside the .NET assembly. While you have to perform a ton of plumbing to build a component in COM, you need to perform zero extra work to get a component in .NET, as all .NET assemblies are components by nature. Remember, we're using the term "component" as a binary, deployable unit, not as a COM class.

Shared Components:
Unlike private assemblies, if shared assemblies used once, they must be published or registered in the system Global Assembly Cache (GAC). When you register your assemblies against the GAC, they act as system components. Again, unlike COM, we don't have to store any information in the system registry for clients to use these shared assemblies.

Object Pooling:
A pool is technical term that refers to a group of resources, such as connections, threads, and objects. Putting a few objects into a pool allows hundreds of clients to share these few objects. Pooling is a technique that minimizes the use of system resources, improves performance, and helps system scalability.

A data reader is a new object providing fast, forward-only, and read-only access to data. This is similar to an ADO Record set with server-side, forward - only, and read-only cursor types.

Even though each Data Adapter maps only one Data Table in the Dataset, you can have multiple adapters to fill the Data Set object with multiple Data Tables.

Managed Code:
The .Net framework provides several core run-time services to the programs that run within it. For example exception handling and security.

What is an Assembly?
Assemblies are fundamental building blocks of .Net Framework. They contain the type and resources that are useful to make an application. Assemblies enables code reuse, version control, security and deployment. An assembly consists of: Manifest, Type Metadata, MSIL and resource file.

Assemblies are Private and Shared. Private are used for a single application and installed in application’s install directory or its sub-directory. Shared assembly is one that can be referenced by multiple applications and resides in GAC.

Metadata and Manifest:
Manifest describes the assembly itself. Assembly name, version, culture, strong name, list of files, type reference and reference assembly. While Metadata describes contents within the assembly like classes, namespaces, interfaces, scope, properties, methods and their parameters etc.

Application Domain:
It is a virtual process that serves to isolate an application. All object created within the same application scope are created within same application domain.

Garbage Collection:
It is Automatic Memory Manager for .Net Framework. It manages the memory allocated to .Net Framework.
When a variable is defined it gets a space in memory (stack) and when an object is created memory for the object is allocated in heap. When an object is assigned to a variable it increments the reference counts for the object and when program control comes out of the function the scope of variable gets ended Or NULL is assigned to variable it decrements the reference count of object by 1. When reference count of one object becomes zero GC acts call destructor of object and then releases the memory acquired by the object.

Can .Net Components can be used from a COM? Yes.
How does .NET Remoting work?
It involves sending messages along channels. Two of the standard channels are HTTP and TCP. TCP is for LANs only and HTTP can be used on LANs or WANs (internet). TCP uses binary serialization and HTTP uses SOAP (.Net Runtime Serialization SOAP Formatter).

There are 3 styles of remote access:
SingleCall: Each incoming request is handled by new instance.
Singleton: All requests are served by single server object.
Client-Activated Object: This is old state-full DCOM model. Where client receives reference to the remote object and keep until it finished with it.

Situations where we have to put same name Dlls in single directory where are Dlls are of different versions.

Boxing and Un-Boxing:
Implicit (automatic) conversion of value type to reference type is known as Boxing And Explicit (manual) conversion of Reference type to value type is said to be Un-boxing. (conversion of Integer variable to object type)

.Net Object Oriented Programming Concepts

Class is concrete representation of an entity. It represents a group of objects, which posses similar attributes and behavior.
Provides Abstraction and Encapsulations. A category name that can be given to group of objects of similar kind.

Object represents/resembles a Physical/real entity. An object is simply something you can give a name.

Object Oriented Programming:
It is a Style of programming that represents a program as a system of objects and enables code-reuse.

Binding of attributes and behaviors. Hiding the implementation and exposing the functionality.

Hiding the complexity. Defining communication interface for the functionality and hiding rest of the things.
In .Net destructor can not be abstract. Can define Either Finalize / Destructor. For Destructor access specifiers can not be assigned. It is Private.

Adding a new method with the same name in same/derived class but with different number/types of parameters. Implements Polymorphism.

When we need to provide different implementation than the provide by base class, We define the same method with same signatures in the derived class. Method must be Protected/Protected-Friend/Public for this purpose. (Base class routine can be called by Mybase.Method, base.Method).

When the method is defined as Final/sealed in base class and not overridable and we need to provide different implementation for the same. We define method with Shadows/new.

Mean by more than one form. Ability to provide different implementation based on different no./type of parameters. A method behaves differently based on the different input parameters. Does not depend on the Return-Type.

Make an method abstract/virtual in base class. Override it in Derived Class. Declare a variable of type base class and assign an object of derived class to it. Now call the virtual/abstract method. The actual method to be called is decided at runtime.

Calling an non-virtual method decides the method to call at compile time is known as Early-Binding.

Identifiers/Access Specifies and scope:
VB.NET: Private, Protected, Friend, Protected Friend, Public.
C#: private, protected, internal, protected internal, public.

What is a Delegate?
A strongly typed function pointer. A delegate object encapsulates a reference to a method. When actual function needs to be called will be decided at run-time.

Static Variable and Its Life-Time:
VB.NET: Public Shared VAR As Type.
C#: public static Type VAR;
Life time is till the class is in memory.

Special Method Always called whenever an instance of the class is created.

Called by GC just before object is being reclaimed by GC.


Different Types of Caching?
Output Caching: stores the responses from an page.
Fragment Caching: Only caches/stores the portion of page (User Control)
Data Caching: is Programmatic way to Cache objects for performance.

Authentication and Authorization:
Authentication is identifying/validating the user against the credentials (username and password) and Authorization performs after authentication. Authorization allowing access of specific resource to user.

Different Types of Directives:
Page, Register, Control, OutputCache, Import, Implements, Assembly, Reference

Difference between Server-Side and Client-Side:
Server-Side code is executed on web-server and does not transmitted to client, while client-side code executed on client(browser) and is rendered to client along with the content.

Difference Server.Transfer and Response.Redirect:
Both ends the processing for the current request immediately. Server.Transfer start executing the another resource specified as parameter without acknowledgement to client(browser) while Response.Redirect intimate client that your requested resource is available at this location and then client request for that resource.

Different Types of Validators and Validation Controls:
RequiredFieldValidator, RangeValidator, RegularExpressionValidator, CompareValidator, CustomValidator, ValidationSummary

How to Manage State in ASP.Net?
Client based: ViewState, QueryString and Cookies Server based: Session, Application.

Difference between User Control and Custom Control:
CUSTOM Controls are compiled code (Dlls), easier to use, difficult to create, and can be placed in toolbox. Drag and Drop controls. Attributes can be set visually at design time. Can be used by Multiple Applications (If Shared Dlls), Even if Private can copy to bin directory of webApp add reference and use. Normally designed to provide common functionality independent of consuming Application.

3 Types of Session State Modes?
InProc(cookieless, timeout),
StateServer (Server, Port stateConnectionString="tcpip=server:port"),
SQLServer (sqlconnectionstring) and Off.

What is ViewState and How it is managed, Its Advantages/Benefits?
ViewState is a special object that ASP.NET uses to maintain the state of page and all webcontrols/ServerControls within it. It is in this object preserves the states of various FORM elements during post-backs. It is rendered to client(browser) as a Hidden variable __VIEWSTATE under

tag. We can also add custom values to it.

What is web.config and machine.config:
machine.config is default configuration for all applications running under this version, located in %WinDir%\Microsfot.Net\Framework\Version. Settings can be overridden by Web.Config for an specific application Web.Config resides in application’s root/virtual root and exists in sub-sequent folders.

Role of Global.asax:
Optional file contains the code to handle Application level events raised by ASP.Net or By HttpModule. This file resides in application root directory. Application_Start, _End, _AuthenticateRequest, _Error, Session_Start, _End, BeginRequest, EndRequest. This file is parsed and compiled into dynamically generated class derived from HttpApplication.

Page Life Cycle:
Init, LoadViewState, LoadPostBackData, Load, RaisePostBackDataChangedEvent, RaisePostBackEvents, Pre-Render, SaveViewState, Render, Unload, (IpostBackDataChangedEventHandler and IpostBackEventHandler) Error, CommitTransaction, AbortTransaction, Abort
inetinfo.exe, aspnet_isapi.dll aspnet_wp.exe, HttpModules (OutputCache, Session, Authentication, Authorization, Custom Modules Specified) and Then HttpHandlers PageHandlerFactory for *.aspx

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 to a subsequent Page?
No assigning value will not work because will be overwritten at the time of rendering. We can assign value to it by register a startup script which will set the action value of form on client-side. Rest are Server.Transfer and Response.Redirect.

ASP.Net List Controls and differentiate between them?
RadioButtonList, CheckBoxList, DropDownList, Repeater, DataGrid, DataList

Type Of Code in Code-Behind class: Server-Side Code.
What might be best suited to place in the Application_Start and Session_Start:
Application level variables and settings initialization in App_Start
User specific variables and settings in Session_Start

Difference between inline and code-behind. Which is best?
Inline is mixed with html and code-behind is separated. Use code-behind, Because Inline pages are loaded, parsed, compiled and processed at each first request to page and remains in compiled code remains in cache until it expires, If expires it again load, parse and compile While code-behind allows to be pre-compiled and provide better performance.

Which Template must provide to display data in Repeater? ItemTemplate.
What method do you use to explicitly kill a user’s Session?

How do you turn off cookies in one page of your application?
We will not use it. But can not turn off cookies from server. To allow or not is a client side functionality.

Which two properties are on every validation control?
ControlToValidate and Text, ErrorMessage
What is the standard you use to wrap up a call to a Web Service? Ans : SOAP
Which method do you use to redirect to user to another page without performing a round trip to Client?

What is transport protocol you use to call a Web-Service SOAP? HTTP-POST

How many classes can a single .NET DLL contain? Unlimited
What is a bubbled event?
When you have a complex control like DataGrid. Writing an event processing routine for each object (cell, button, row etc.). DataGrid handles the events of its constituents and will raise its own defined custom events.

Layouts of ASP.NET Pages: GridLayout and FlowLayout

Web User Control:
Combines existing Server and HTML controls by using VS.Net. to create functional units that encapsulate some aspects of UI. Resides in Content Files, which must be included in project in which the controls are used.

Composite Custom Control : combination of existing HTML and Server Controls.

should Validation occur on Client/Server Side for Date Input?
Both. Client-side reduces extra round-trip. Server-Side ensures prevention against hacking and failure against automated requests.

As their names imply, both HTTP GET and HTTP POST use HTTP as their underlying protocol. Both of these methods encode request parameters as name/value pairs in the HTTP request. The GET method creates a query string and appends it to the script's URL on the server that handles the request. For the POST method, the name/value pairs are passed in the body of the HTTP request message.

Lifecycle Of A Web Form:
In ASP .NET, the web page starts its life when a client requests a particular page. IIS parses and runs the scripts on the ASP page to render HTML content. As soon as the page rendering is complete, the page's life ceases; only the view states of the page persist between requests to the page. These view states allow the controls on the server to appear as if they are still present to handle server events.

ASP.NET Session-State Management:
ASP.NET improves upon ASP session-state management by moving to an out-of-process model. By having all web servers in the farm pointing to a common server that hosts the out-of-process state manager, the web client can be redirected around the farm without losing the session states. By using an out-of-process model, we no longer have the problem of losing session states when the IIS process is cycled. This means that if the web server application crashed for whatever reason and restarted within the session time-out duration, the web clients could still have all their session states intact. Of course, if the out-of-process state manager crashed, that is a whole different issue. This leads to the next improvement of ASP.NET—the ability to persist session state to a database.

There are two levels of configuration: machine and application. Machine-level configuration associates with the machine.config file stored in WinNT\Microsoft.NET\ Framework\\CONFIG\machine.config, while the application-level configuration uses the web.config file in the application root directory. The application-level configuration overrides the machine -level configuration.



COM Callable Wrapper


Common Language Infrastructure. This is a subset of the CLR and base class libraries that Microsoft has submitted to ECMA so that a third-party vendor can build a .NET runtime on another platform.


Common Object File Format


Discovery of Web Services. A Web Service has one or more. DISCO files that contain information on how to access its WSDL.


Distributed interNet Applications Architecture.


Globally Unique Identifier


Interface Definition Language


Microsoft Distributed Transaction Coordinator


Online Transaction Processing


Online Analytical Processing


Portable Executable


Rapid Application Development


Runtime Callable Wrapper


Simple Mail Transfer Protocol


Transport Control Protocol


Type Library


Uniform Data Format


User Interface


Uniform Resource Locator


Universal Description, Discovery and Integration


Wireless Access Protocol


Web Services Definition Language


Wireless Markup Language

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