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 ASP.Net Interview Questions
 
Explain the page life cycle in ASP.NET 2.0

ASP.NET 2.0 Page Life Cycle - The lifetime of an ASP.NET page is filled with events. A series of processing steps takes place during this page life cycle. Following tasks are performed:

* Initialization
* Instantiation of controls
* Restoration & Maintainence of State
* Running Event Handlers
* Rendering of data to the browser

The life cycle may be broken down into Stages and Events. The stages reflect the broad spectrum of tasks performed. The following stages take place

1) Page Request - This is the first stage, before the page life cycle starts. Whenever a page is requested, ASP.NET detects whether the page is to be requested, parsed and compiled or whether the page can be cached from the system.
2) Start - In this stage, properties such as Request and Response are set. Its also determined at this stage whether the request is a new request or old, and thus it sets the IsPostBack property in the Start stage of the page life cycle.
3) Page Initialization - Each control of the page is assigned a unique identification ID. If there are themes, they are applied. Note that during the Page Initialization stage, neither postback data is loaded, nor any viewstate data is retrieved.
4) Load - If current request is a postback, then control values are retrieved from their viewstate.
5) Validation - The validate method of the validation controls is invoked. This sets the IsValid property of the validation control.
6) PostBack Event Handling - Event handlers are invoked, in case the request is a postback.
7) Rendering - Viewstate for the page is saved. Then render method for each control is called. A textwriter writes the output of the rendering stage to the output stream of the page's Response property.
8) Unload - This is the last stage in the page life cycle stages. It is invoked when the page is completely rendered. Page properties like Respone and Request are unloaded.

Note that each stage has its own events within it. These events may be used by developers to handle their code. Listed below are page events that are used more frequently.

PreInit - Checks the IsPostBack property. To create or recreate dynamic controls. To set master pages dynamically. Gets and Sets profile propety values.
Init - Raised after all controls are initialized, and skin properties are set.
InitComplete - This event may be used, when we need to be sure that all initialization tasks are complete.
PreLoad - If processing on a control or a page is required before the Load event.
Load - invokes the OnLoad event on the page. The same is done for each child control on the page. May set properties of controls, create database connections.
Control Events - These are the control specific events, such as button clicks, listbox item selects etc.
LoadComplete - To execute tasks that require that the complete page has been loaded.
PreRender - Some methods are called before the PreRenderEvent takes place, like EnsureChildControls,

Acronyms in .NET.. Explained..

ADO - ActiveX Data Object - Microsoft ActiveX Data Objects (ADO) is a collection of Component Object Model objects for accessing different types of data sources.

AJAX - Asynchronouse Javascript and XML - Ajax is a web development technology used for creating interactive web pages with fast data rendering by enabling partial postbacks on a web page (That means a section of the web page is rendered again, instead of the complete web page. This is achieved using Javascript, XML, JSON (Javascript Notation Language) and the XMLHttpRequest object in javascript.

ASP - Active Server Pages - Microsoft's Server side script engine for creating dynamic web page.

C# - C Sharp - Microsoft Visual C# is an object oriented programming language based on the .NET Framework. It includes features of powerful languages like C++, Java, Delphi and Visual Basic.

CAO - Client Activated Object - Objects created on the server upon the client's request. This is used in Remoting.

CCW - COM Callable Wrapper - This component is used when a .NET component needs to be used in COM.

CIL - Common Intermediate Language - Its actually a low level human readable language implementation of CLI. All .NET-aware languages compile the source oode to an intermediate language called Common Intermediate Language using the language specific compiler.

CLI - Common Language Infrastructure - This is a subset of 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.

CLR - Common Language Runtime - It is the main runtime machine of the Microsoft .NET Framework. It includes the implementation of CLI. The CLR runs code in the form of bytes, called as bytecode and this is termed MSIL in .NET.

CLS - Common Language Specification - A type that is CLS compliant, may be used across any .NET language. CLS is a set of language rules that defines language standards for a .NET language and types declared in it. While declaring a new type, if we make use of the [CLSCompliant] attribute, the type is forced to conform to the rules of CLS.

COFF - Common Object File Format - It is a specification format for executables.

COM - Component Object Model - reusable software components. The tribe of COM components includes COM+, Distributed COM (DCOM) and ActiveX® Controls.

CSC.exe - C Sharp Compiler utility

CTS - Common Type System - It is at the core of .NET Framework's cross-language integration, type safety, and high-performance code execution. It defines a common set of types that can be used with many different language syntaxes. Each language (C#, VB.NET, Managed C++, and so on) is free to define any syntax it wishes, but if that language is built on the CLR, it will use at least some of the types defined by the CTS.

DBMS - Database Management System - a software application used for management of databases.

DISCO - Discovery of Web Services. A Web Service has one or more. DISCO<

Whats the difference between MSIL and CIL?

MSIL is the name given to the intermediate language in .NET Framework Beta, 1.0 and 1.1. From version 2.0 onwards, the intermediate language is called CIL. We can say, MSIL is the old name. MSIL stands for Microsoft Intermediate Language. CIL stands for Common Intermediate Language. Its actually a low level human readable language implementation of CLI.

There is not much difference between the two. Compilers like vbc.exe and csc.exe compile the code into intermediate language. CIL is the name submitted by Microsoft to the European Computer Manufacturer's Association(ECMA) as a standard.

What is the difference between Overriding and Shadowing?

Both Overriding and Shadowing are ways to alter the behaviour of members of a base class. Shadowing is a VB.NET concept. In C#, this concept is called Hiding, though there is a difference between the two.

When we do shadowing, we provide a new implementation to the base class member without overriding it. We may shadow a base class member in a derived class, by using the keyword shadows. The access level, return type, and the signature (means the datatypes of the arguments passed & the order of the types) of the derived class members which are shadowed, may differ from the base class.

In C#, we may achieve shadowing using the keyword new. However, when Hiding in C#, the access level, the signature, return type of the derived class must be same as the base class.

Overriding is the concept of providing a new implementation of derived class member as compared to its based class. In VB.NET, we do overriding using the overrides keyword, while in C#, overriding is achieved using the override keyword. For a class member to be overridable, we use the keyword virtual while defining it (in C#), and we use the keyword overridable (in VB.NET), though if we leave out specifying the overridable keyword, the member is overridable by default.

Whats the difference betweeen Structure, Class and Enumeration

Structures and Enumerations are Value-Types. This means, the data that they contain is stored as a stack on the memory. Classes are Reference-Types, means they are stored as a heap on the memory.
Structures are implicitly derived from a class called System.ValueType. The purpose of System.ValueType is to override the virtual methods defined by System.Object. So when the runtime encounters a type derived from System.ValueType, then stack allocation is achieved. When we allocate a structure type, we may also use the new keyword. We may even make a constructor of a structure, but, remember, A No-argument constructor for a structure is not possible. The structure's constructor should always have a parameter.

So if we define the following structure

struct MyStruct
{
  public int y,z;
}
and we create a structure type
MyStruct st = new MyStruct();
In case of a class, no-argument constructors are possible. Class is defined using the class keyword.
A struct cannot have an instance field, whereas a class can.
class A
{
int x = 5; //No error
...
}

struct
{
int x = 5; //Syntax Error
}
A class can inherit from one class (Multiple inheritance not possible). A Structure cannot inherit from a structure.
Enum is the keyword used to define an enumeration. An enumeration is a distinct type consisting of a set of named constants called the enumerator list. Every enumeration has an underlying type. The default type is "int". Note: char cant be the underlying data type for enum. First value in enum has value 0, each consequent item is increased by 1.
enum colors {red, green, blue, yellow};

Here, red is 0, green is 1, blue is 2 and so on.
An explicit casting is required to convert an enum value to its underlying type

int x = (int)colors.yellow;
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