NET Interview Questions

.Net Interview Questions Quick Reference and FAQ General questions specifically from IT and .NET interviews point of view. Best for Fresher and students who want to have a feel of what .NET questions are asked in multinational companies.

2011

Abhishek Goenka CIBERSITES INDIA

Version 1.0

P a g e | 2 Prepared by Abhishek Goenka

Email – [email protected]

.Net Interview Questions 2011

ASP.Net Interview Questions

From constructor to destructor (taking into consideration Dispose() and the concept of non-

deterministic finalization), what are the events fired as part of the ASP.NET System.Web.UI.Page

lifecycle. Why are they important? What interesting things can you do at each?

As all of us know a request comes from Client (Browser) and sends to Server (we call it as Web server) in

turn server process the request and sends response back to the client in according to the client request.

But internally in the web server there is quite interesting process that happens. To get aware of that

process we should first of all know about the architecture of the IIS

It mainly consists of 3 Parts/Files

Inetinfo.exec

ISAPI Filer (Container for Internet Server Application Interface dlls),

Worker Process (aspnet_wp.exe)

Inetinfo.exe is the ASP.Net request handler that handles the requests from the client .If it's for static resources like HTML files or image files inetinfo.exe process the request and sent to client. If the request is with extension aspx/asp, inetinfo.exe processes the request to API filter. ISAPI filter will have several runtime modules called as ISAPI extensions. To process the request ISAPI filter takes the help of these runtime modules. The runtime module loaded for ASP page is asp.dll. And for ASP.NET page it's ASPNET_ISAPI.dll. From here the request is processed to the "worker process". Worker Process will have several application domains.

Worker process sends the request to HTTPPIPE line.(HTTP Pipeline is nonetheless collection of .net framework classes). HTTP Pipeline compiles the request into a library and makes a call to HTTP runtime and runtime creates an instance of page class public class File : System.Web.UI.Page {} ASP.Net web page is a class derived from page class, this page class resides in system.web.dll After creating instance pf page class HTTP Runtime immediately invokes process request method of page class Page Req = new Page(); Req.ProcessRequest();




Page Event Typical Use

PreInit

Raised after the start stage is complete and before the initialization stage begins. Use this event for the following:

Check the IsPostBack property to determine whether this is the first time the page is being processed. The IsCallback and IsCrossPagePostBack properties have also been set at this time.

Create or re-create dynamic controls.

Set a master page dynamically.

Set the Theme property dynamically.

Read or set profile property values.

Init

Raised after all controls have been initialized and any skin settings have been applied. The Init event of individual controls occurs before the Init event of the page. Use this event to read or initialize control properties.

InitComplete

Raised at the end of the page's initialization stage. Only one operation takes place between the Init and InitComplete events: tracking of view state changes is turned on. View state tracking enables controls to persist any values that are programmatically added to the ViewState collection. Until view state tracking is turned on, any values added to view state are lost across postbacks. Controls typically turn on view state tracking immediately after they raise their Init event. Use this event to make changes to view state that you want to make sure are persisted after the next postback.

PreLoad Raised after the page loads view state for itself and all controls, and after it processes postback data that is included with the Request instance.

Load

The Page object calls the OnLoad method on the Page object, and then recursively does the same for each child control until the page and all controls are loaded. The Load event of individual controls occurs after the Load event of the page. Use the OnLoad event method to set properties in controls and to establish database connections.

Control events Use these events to handle specific control events, such as a Button control's Click event or a TextBox control's TextChanged event.

LoadComplete Raised at the end of the event-handling stage. Use this event for tasks that require that all other controls on the page be loaded.

PreRender

Raised after the Page object has created all controls that are required in order to render the page, including child controls of composite controls. (To do this, the Page object calls EnsureChildControls for each control and for the page.) The Page object raises the PreRender event on the Page object, and then recursively does the same for each child control. The PreRender event of individual controls occurs after the PreRender event of the page.




Use the event to make final changes to the contents of the page or its controls before the rendering stage begins.

PreRenderComplete Raised after each data bound control whose DataSourceID property is set calls its DataBind method. For more information, see Data Binding Events for Data-Bound Controls later in this topic.

SaveStateComplete Raised after view state and control state have been saved for the page and for all controls. Any changes to the page or controls at this point affect rendering, but the changes will not be retrieved on the next postback.

Render

This is not an event; instead, at this stage of processing, the Page object calls this method on each control. All ASP.NET Web server controls have a Render method that writes out the control's markup to send to the browser. If you create a custom control, you typically override this method to output the control's markup. However, if your custom control incorporates only standard ASP.NET Web server controls and no custom markup, you do not need to override the Render method. For more information, see Developing Custom ASP.NET Server Controls. A user control (an .ascx file) automatically incorporates rendering, so you do not need to explicitly render the control in code.

Unload

Raised for each control and then for the page. In controls, use this event to do final cleanup for specific controls, such as closing control-specific database connections. For the page itself, use this event to do final cleanup work, such as closing open files and database connections, or finishing up logging or other request-specific tasks.

Although both Init and Load recursively occur on each control, they happen in reverse order. The Init

event (and also the Unload event) for each child control occur before the corresponding event is raised

for its container (bottom-up). However the Load event for a container occurs before the Load events for

its child controls (top-down). Master pages behave like child controls on a page: the master page Init

event occurs before the page Init and Load events, and the master page Load event occurs after the

page Init and Load events.

What is EnableViewStateMAC?

Setting EnableViewStateMac=true is a security measure that allows ASP.NET to ensure that the

viewstate for a page has not been tampered with. If on Postback, the ASP.NET framework detects that

there has been a change in the value of viewstate that was sent to the browser, it raises an error -

Validation of viewstate MAC failed.

Use <%@ Page EnableViewStateMac="true"%> to set it to true (the default value, if this attribute is not

specified is also true) in an aspx page.

But this has a side effect: it also prevents multiple servers from processing the same ViewState. One

solution is to force every server in your farm to use the same key-- generate a hex encoded 64-bit or

128-bit <machineKey> and put that in each server's machine.config :



<machineKey validation="SHA1"

validationKey="F3690E7A3143C185A6A8B4D81FD55DD7A69EEAA3B32A6AE813ECEEC" />

What is the difference between asp:Label and asp:Literal control?

asp:Label control

asp:Label control is used to write text on the page with different formatting options like bold, italic,

underlined etc

asp:Literal control

Ideally Literal control is the rarely used control which is used to put static text on the web page. When it

is rendered on the page, it is implemented just as a simple text.

Unlike asp:Label control, there is no property like BackColor, ForeColor, BorderColor, BorderStyle,

BorderWidth, Height etc. of Literal control. That makes it more powerful, you can even put a pure HTML

contents into it.

What’s a SESSION and APPLICATION object?

Viewstate - Viewstate is a hidden fields in an ASP.NET page, contains state of those controls on a page

whose "EnableViewstate" property is "true".

You can also explicitly add values in it, on an ASP.NET page like:

Viewstate.Add( "TotalStudents", "87" );

Viewstate should be used when you want to save a value between different roundtrips of a single page

as Viewstate of a page is not accessible by another page. Because Viewstate renders with the page, it

consumes bandwidth, so be careful to use it in applications to be run on low bandwidth.

Session Variable - Session variables are usually the most commonly used. When a user visits a site, it's

sessions starts and when the user become idle or leave the site, the session ends. Session variables

should be used to save and retrieve user specific information required on multiple pages. Session

variables consumes server memory, so if your may have a huge amount visitors, use session very

carefully and instead of put large values in it try to put IDs and references

Application variables - Application variables are shared variables among all users of a web application.

Application variables behave like static variables and they are substitute of static variables as static

variables are stateless in web applications. Only shared values should be persisted in Application

variables, and as soon as they are not in use they should be removed explicitly.

Cache - Cache is probably the least used state feature of ASP.NET. Cache is basically a resource specific

state persistence feature, means unlike session it stick with resource instead of user, for instance: pages,




controls etc. Cache should be used or frequently used pages, controls, and data structures. Data cache

can be used to cache frequently used list of values e.g. list of products

Cookies - Cookies are some values saved in browsers by the website to retrievable and use afterwards.

Usually cookies are used to help dynamic websites to identify visitors and retrieve their saved

preferences. Cookies are also used to facilitate auto login by persisting user id in a cookie save in user's

browser. Because cookies have been saved at client side, they do not create performance issues but

may create security issues as they can be hacked from browser.

What are the different types of caching?

CachingOutput Caching - We can use Page output for those page which content are relatively static. So

rather than generating the page on each user request we can cached the page using Page output

caching so that it can be access from cache itself. So, Instead of pages can be generated once and then

cached for subsequent request. Page output caching allows the entire content of a given page to be

stored in the cache.

<%@ Page Language="C#" %>

<%@ OutputCache Duration='300' VaryByParam='none' %>

Fragment caching - ASP.NET provides a mechanism for caching portions of pages, called page fragment

caching. To cache a portion of a page, you must first encapsulate the portion of the page you want to

cache into a user control. In the user control source file, add an OutputCache directive specifying the

Duration and VaryByParam attributes. When that user control is loaded into a page at runtime, it is

cached, and all subsequent pages that reference that same user control will retrieve it from the cache.

<!— UserControl.ascx —>

<%@ OutputCache Duration='60'

VaryByParam='none' %>

<%@ Control Language="'C#'" %>

Data Caching - Caching of data can dramatically improve the performance of an application by reducing

database contention and round-trips. Simply data caching store the required data in cache so that web

server did not send request to DB server every time for each and every request which increase the web

site performance.

There are three Different ways to add data or object into cache. But based upon the situation we have

to access it. These methods are Cache[], Cache.add(), cache.insert(). The following table will show you

the clear difference of these methods.

Is it possible to prevent a browser from caching an ASPX page?

Just call SetNoStore on the HttpCachePolicy object exposed through the Response object's Cache

property, as demonstrated here:




What does AspCompat="true" mean and when should I use it?

The AspCompat attribute forces the page to execute in STA mode. The runtime throws an exception if

the compatibility tag is omitted and an STA component is referenced on the page. If you convert the STA

component to an assembly using Tlbimp.exe, the runtime does not detect that the component uses the

STA model and does not throw an exception, but your application can suffer from poor performance.

<%@Page AspCompat=true Language = VB%>

What are the main event handlers in Global.asax?

ASP.NET provides several modules that participate in each request and expose events you can handle in

Global.asax. You can customize and extend these modules as you like, or develop completely new

custom modules to process information for and about HTTP requests made to your ASP.NET-based

application. Following are important events catered for in the Global.asax file.

Application_Init: Fires when the application initializes for the first time.

Application_Start: Fires the first time an application starts.

Session_Start: Fires the first time when a user’s session is started.

Application_BeginRequest: Fires each time a new request comes in.

Application_EndRequest: Fires when the request ends.

Application_AuthenticateRequest: Indicates that a request is ready to be authenticated.

Application_Error: Fires when an unhandled error occurs within the application.

Session_End: Fires whenever a single user Session ends or times out.

Application_End: Fires when the application ends or times out (Typically used for application

cleanup logic).

What are different types of directives in .NET?

@Page: Defines page-specific attributes used by the ASP.NET page parser and compiler. Can be included

only in .aspx files <%@ Page AspCompat="TRUE" language="C#" %>

@Control: Defines control-specific attributes used by the ASP.NET page parser and compiler. Can be

included only in .ascx files. <%@ Control Language="VB" EnableViewState="false" %>




@Import: Explicitly imports a namespace into a page or user control. The Import directive cannot have

more than one namespace attribute. To import multiple namespaces, use multiple @Import directives.

<% @ Import Namespace="System.web" %>

@Implements: Indicates that the current page or user control implements the specified .NET framework

interface.<%@ Implements Interface="System.Web.UI.IPostBackEventHandler" %>

@Register: Associates aliases with namespaces and class names for concise notation in custom server

control syntax.<%@ Register Tagprefix="Acme" Tagname="AdRotator" Src="AdRotator.ascx" %>

@Assembly: Links an assembly to the current page during compilation, making all the assembly's classes

and interfaces available for use on the page. <%@ Assembly Name="MyAssembly" %><%@ Assembly

Src="MySource.vb" %>

@OutputCache: Declaratively controls the output caching policies of an ASP.NET page or a user control

contained in a page<%@ OutputCache Duration="#ofseconds" Location="Any | Client | Downstream |

Server | None" Shared="True | False" VaryByControl="controlname" VaryByCustom="browser |

customstring" VaryByHeader="headers" VaryByParam="parametername" %>

@Reference: Declaratively indicates that another user control or page source file should be dynamically

compiled and linked against the page in which this directive is declared.

What are ASHX files? What are HttpHandlers? Where can they be configured?

ASP.NET programming supports the creation of custom HttpHandler components, which provide a

flexible and efficient way to process requests that don't return standard HTML-based pages. For

example, HttpHandler components are great for situations in which you want to return simple text,

XML, or binary data to the user.

The easiest way to create a custom HttpHandler component is to create a source file with an .ashx

extension. You must then add a @WebHandler directive to the top of the .ashx file, along with a class

definition that implements the IHttpHandler interface. Any class that implements the IHttpHandler

interface must provide an implementation of the IsReusable method and the ProcessRequest method. <%@ Assembly Name="Microsoft.SharePoint, [full assembly name]" %>

<%@ WebHandler Language="C#" Class="HelloHttpHandler" %>

using System;

using System.Web;

using Microsoft.SharePoint;

public class HelloHttpHandler : IHttpHandler {

public bool IsReusable {

get { return false; }

}

public void ProcessRequest(HttpContext context) {

SPSite siteColl = SPContext.Current.Site;

SPWeb site = SPContext.Current.Web;

context.Response.ContentType = "text/plain"

context.Response.Write("Hello HttpHandler from the site " +

site.Title +

" at " +

site.Url);

}

}




After you deploy your .ashx file within a directory nested within the \LAYOUTS directory, it is accessible

to any site in the farm by using a site-relative path. http://MyWebServer/sites/Sales/_layouts/Litware/HelloHttpHandler.ashx

What is needed to configure a new extension for use in ASP.NET? For example, what if I wanted my

system to serve ASPX files with a *.jsp extension?

It is possible to configure new extension for use in ASP.Net. This as to be configured in IIS actually in

order for IIS to route your pages to the proper ISAPI

Follow this: http://blogs.msdn.com/gduthie/archive/2007/03/14/custom-file-extensions-in-asp-net-2-

0.aspx

What events fire when binding data to a data grid? What are they good for?

ItemCreated: The ItemCreated event is fired when an item in a DataGrid control is created. This means

that at the time the event is fired, the DataGrid does not yet know about the data that will be bound to

it. So, if the logic of your method depends on this data being available to the control, you’re better off

using the ItemDataBound event. Other than that, the ItemCreate event differentiates itself in one other

way from the ItemDataBound event: the ItemCreated event is raised when data is bound to the control

and during round-trips (postbacks). These qualities make the event especially well-suited to add custom

attributes to a DataRow (such as onmouseover or other javascript events) or to control the appearance

in ways that do not depend on the data within the DataRow (such as making every 10th row a different

color).

ItemDataBound: The ItemDataBound event is fired after after an item in a DataGrid control is bound.

This means that (unlike the ItemCreated event) you can add special formatting to a DataRow that is

dependent upon the data contained within that row. Since ItemDataBound is fired after the

ItemCreated event, it is within this event that you are presented with the final opportunity to access the

data before it is rendered to the client. These qualities make the event well-suited for changing the

appearance of a row or cell based on the data within that row or cell (such as highlighting outliers or

other important information).Example:

Assume we have the following DataGrid declared on our .aspx page:

<asp:DataGrid ID="MainDataGrid"

runat="server"

AutoGenerateColumns="true"

OnItemDataBound="MainDataGrid_ItemDataBound"

OnItemCreated="MainDataGrid_ItemCreated" />

On the code behind page then, we can create the following two methods to handle adding

titles to header row, to specify more descriptive headers, and to change the row background color based on an employee’s salary:

http://blogs.msdn.com/gduthie/archive/2007/03/14/custom-file-extensions-in-asp-net-2-0.aspx

http://blogs.msdn.com/gduthie/archive/2007/03/14/custom-file-extensions-in-asp-net-2-0.aspx




protected void MainDataGrid_ItemCreated(object sender, DataGridItemEventArgs e)

{

//If the item is in the header

if (e.Item.ItemType == ListItemType.Header)

{

//Iterate through each cell

foreach(TableCell item in e.Item.Cells)

{

//Add the title attribute — we could just as easily

//add a javascript onmouseover event here

item.Attributes.Add("title", item.Text);

}

//Since the header values are set before we have access

//to the data, we can modify the third column header to

//be a bit more descriptive

e.Item.Cells[2].Text = "Salary (in US$)";

} }

protected void MainDataGrid_ItemDataBound(object sender, DataGridItemEventArgs e)

{

//Since DataGrid differentiates between Items and AlternatingItems, you sometimes

have to check

//for one *or* the other

if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.Alternating

Item)

{

//Here we will modify the row color based on the salary

//We can only do this within ItemDataBound since it relies

//on the data being available from the data source

if (Convert.ToInt32(e.Item.Cells[2].Text) < 10000)

{

e.Item.BackColor = System.Drawing.Color.LightPink;

}

else if (Convert.ToInt32(e.Item.Cells[2].Text) < 1000000)

{

e.Item.BackColor = System.Drawing.Color.LightBlue;

}

else

{

e.Item.BackColor = System.Drawing.Color.LightGreen;

}

}

}




ASP.NET Code Block Types

Interaction with the page from these blocks is limited, since the code is executed during the render

phase of the page life cycle <% Trace.Warn("Embedded Code Block", "Hello World"); %>

Let’s have a look at the different types of syntax we can use for code blocks in ASP.NET pages. There are

really four types of code blocks, and the first one is different from the others:

<%$ %>

<%# %>

<% %>

<%= %>

ASP.NET Expression Syntax

First of all we have ASP.NET expressions which look like <%$ AppSettings:Key %> <asp:Label runat="server" Text="<%$ AppSettings:Key %>" />

ASP.NET Data-Binding syntax

The next code construct is the data-binding syntax: <%# Eval("Value") %> which is used to bind to

properties to data on demand.

Statement and Expression/Evaluated Code Blocks

Display some values <%

string message = "Hello World!";

Response.Write(message);

%>

These are delimited by <%= and %> and the content of this code block becomes the parameter to the

HtmlTextWrite.Write() method. Therefore, the code inside this type of code block should be an

expression, and not a statement. <%= String.Format("The title of this page is: {0}", this.Title ?? "n/a") %>

What method do you use to explicitly kill a user s session?

Session.Abandon

Which two properties are on every validation control?

1. ControlToValidate

2. ErrorMessage

What are the validation controls in asp.net?

There are 5 validation controls in asp.net

1. RequiredFieldValidator

2. RangeValidator

3. RegularExpressionValidator

4. CompareValidator

5. CustomValidator




ValidationSummary is not a validation control but a control that displays summary of all error occurs

while validating the page.

How to load a user control dynamically in runtime?

Control c = (Control)Page.LoadControl("~/usercontrol/MyUserControl.ascx");

Page.Form.Controls.Add(c);

How to get the authentication mode from web.config file programmatically at runtime?

System.Web.Configuration.AuthenticationSection section =

(AuthenticationSection)WebConfigurationManager.GetSection("system.web/authentication");

Label1.Text = section.Mode.ToString();

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

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

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 event handlers, allowing the

main DataGrid event handler to take care of its constituents.

ASP.NET Compilation Tool (Aspnet_compiler.exe)

The ASP.NET Compilation tool (Aspnet_compiler.exe) enables you to compile an ASP.NET Web

application, either in place or for deployment to a target location such as a production server. In-place

compilation helps application performance because end users do not encounter a delay on the first

request to the application while the application is compiled.

Compilation for deployment can be performed in one of two ways: one that removes all source files,

such as code-behind and markup files, or one that retains the markup files.

What is different between WebUserControl and in WebCustomControl?

Web user controls :- Web User Control is Easier to create and another thing is that its support is limited

for users who use a visual design tool one good thing is that its contains static layout one more thing a

separate copy is required for each application.

Web custom controls: - Web Custom Control is typical to create and good for dynamic layout and

another thing is that it has full tool support for user and a single copy of control is required because it is

placed in Global Assembly cache.

What is smart navigation?

Enable smart navigation by using the Page.SmartNavigation property. When you set the

Page.SmartNavigation property to true, the following smart navigation features are enabled:




The scroll position of a Web page is maintained after postback.

The element focus on a Web page is maintained during navigation.

Only the most recent Web page state is retained in the Web browser history folder.

The flicker effect that may occur on a Web page during navigation is minimized.

Note: Smart navigation is deprecated in Microsoft ASP.NET 2.0 and is no longer supported by Microsoft

Product Support Services

How many types of cookies are there in ASP.NET ?

In-memory cookies: An in-memory cookie goes away when the user shuts the browser down.

Persistent cookies: A persistent cookie resides on the hard drive of the user and is retrieved

when the user comes back to the Web page.

If you create a cookie without specifying an expiration date, you are creating an in-memory cookie,

which lives for that browser session only. The following illustrates the script that would be used for an

in-memory cookie: Response.Cookies("SiteArea") = "TechNet"

The following illustrates the script used to create a persistent cookie: Response.Cookies("SiteArea") = "TechNet"

Response.Cookies("SiteArea").Expires = "August 15, 2000"

TODO List

Explain how PostBacks work, on both the client-side and server-side. How do I chain my own JavaScript?

How does ViewState work and why is it either useful or evil?

What is the OO relationship between an ASPX page and its CS/VB code behind file in ASP.NET 1.1? In

2.0?

What happens from the point an HTTP request is received on a TCP/IP port up until the Page fires the

On_Load event?

How does IIS communicate at runtime with ASP.NET? Where is ASP.NET at runtime in IIS5? IIS6?

What is an assembly binding redirect? Where are the places an administrator or developer can affect

how assembly binding policy is applied?

Compare and contrast LoadLibrary(), CoCreateInstance(), CreateObject() and Assembly.Load().




ASP.NET MVC 3 Interview Questions What is MVC?

MVC is a framework methodology that divides an application’s implementation into three component

roles: models, views, and controllers.

“Models” in a MVC based application are the components of the application that are responsible for

maintaining state. Often this state is persisted inside a database (for example: we might have a Product

class that is used to represent order data from the Products table inside SQL).

“Views” in a MVC based application are the components responsible for displaying the application’s

user interface. Typically this UI is created off of the model data (for example: we might create an

Product “Edit” view that surfaces textboxes, dropdowns and checkboxes based on the current state of a

Product object).

“Controllers” in a MVC based application are the components responsible for handling end user

interaction, manipulating the model, and ultimately choosing a view to render to display UI. In a MVC

application the view is only about displaying information – it is the controller that handles and responds

to user input and interaction.

Which are the advantages of using MVC Framework?

MVC is one of the most used architecture pattern in ASP.NET and this is one of those ASP.NET interview

question to test that do you really understand the importance of model view controller.

It provides a clean separation of concerns between UI and model.

1. UI can be unit test thus automating UI testing.

2. Better reuse of views and model. You can have multiple views which can point to the same

model and also vice versa.

3. Code is better organized.

What is Razor View Engine?

Razor view engine is a new view engine created with ASP.Net MVC model using specially designed Razor

parser to render the HTML out of dynamic server side code. It allows us to write Compact, Expressive,

Clean and Fluid code with new syntaxes to include server side code in to HTML.

What is namespace of asp.net MVC?

ASP.NET MVC namespaces and classes are located in the System.Web.Mvc assembly.

System.Web.Mvc namespace

Contains classes and interfaces that support the MVC pattern for ASP.NET Web applications. This

namespace includes classes that represent controllers, controller factories, action results, views, partial

views, and model binders.

System.Web.Mvc.Ajax namespace

Contains classes that support Ajax scripts in an ASP.NET MVC application. The namespace includes

support for Ajax scripts and Ajax option settings.

System.Web.Mvc.Async namespace

Contains classes and interfaces that support asynchronous actions in an ASP.NET MVC application




System.Web.Mvc.Html namespace

Contains classes that help render HTML controls in an MVC application. The namespace includes classes

that support forms, input controls, links, partial views, and validation.

How to identify AJAX request with C# in MVC.NET?

The solution is in depended from MVC.NET framework and universal across server-side technologies.

Most modern AJAX applications utilize XmlHTTPRequest to send async request to the server. Such

requests will have distinct request header:

X-Requested-With = XMLHTTPREQUEST

MVC.NET provides helper function to check for Ajax requests which internally inspects X-Requested-

With request header to set IsAjax flag.

HelperPage.IsAjax Property

Gets a value that indicates whether Ajax is being used during the request of the Web page.

Namespace: System.Web.WebPages

Assembly: System.Web.WebPages.dll

However, same can be achieved by checking requests header directly:

Request["X-Requested-With"] == “XmlHttpRequest”

What is Repository Pattern in ASP.NET MVC?

Repository pattern is useful for decoupling entity operations form presentation, which allows easy

mocking and unit testing.

“The Repository will delegate to the appropriate infrastructure services to get the job done.

Encapsulating in the mechanisms of storage, retrieval and query is the most basic feature of a Repository

implementation”

“Most common queries should also be hard coded to the Repositories as methods.”




Which MVC.NET to implement repository pattern Controller would have 2 constructors on

parameterless for framework to call, and the second one which takes repository as an input:

class myController: Controller

{

private IMyRepository repository;

// overloaded constructor

public myController(IMyRepository repository)

{

this.repository = repository;

}

// default constructor for framework to call

public myController()

{

//concreate implementation

myController(new someRepository());

}

...

public ActionResult Load()

{

// loading data from repository

var myData = repository.Load();

}

}

What is difference between MVC (Model-View-Controller) and MVP(Model-View-Presenter)?

The main difference between the two is how the manager (controller/presenter) sits in the overall

architecture.

All requests go first to the Controller

MVC pattern puts the controller as the main ‘guy’ in charge for running the show. All application request

comes through straight to the controller, and it will decide what to do with the request.

Giving this level of authority to the controller isn’t an easy task in most cases. Users interaction in an

application happen most of the time on the View.

Thus to adopt MVC pattern in a web application, for example, the url need to become a way of

instantiating a specific controller, rather than ‘simply’ finding the right View (webform/ html page) to

render out. Every requests need to trigger the instantiation of a controller which will eventually produce

a response to the user.




This is the reason why it’s alot more difficult to implement pure MVC using Asp.Net Webform. The Url

routing system in Asp.Net webform by default is tied in to the server filesystem or IIS virtual directory

structure. Each of these aspx files are essentially Views which will always get called and instantiated first

before any other classes in the project. (Of course I’m overgeneralizing here. Classes like IHttpModule,

IHttpHandler and Global.asax would be instantiated first before the aspx web form pages).

MVP (Supervising Controller) on the other hand, doesn’t mind for the View to take on a bigger role.

View is the first object instantiated in the execution pipeline, which then responsible for passing any

events that happens on itself to the Presenter.

The presenter then fetch the Models, and pass it back to the view for rendering.

What is the ‘page lifecycle’ of an ASP.NET MVC?

Following process are performed by ASP.Net MVC page:

1) App initialization

2) Routing

3) Instantiate and execute controller

4) Locate and invoke controller action

5) Instantiate and render view

How to call javascript function on the change of Dropdown List in ASP.NET MVC?

Create a java-script function:

<script type="text/javascript">

function selectedIndexChanged() {

}

</script>

Call the function:

<%:Html.DropDownListFor(x => x.SelectedProduct,

new SelectList(Model.Products, "Value", "Text"),

"Please Select a product", new { id = "dropDown1",

onchange="selectedIndexChanged()" })%>

How route table is created in ASP.NET MVC?

When an MVC application first starts, the Application_Start() method is called. This method, in turn, calls

the RegisterRoutes() method. The RegisterRoutes() method creates the route table.

How do you avoid XSS Vulnerabilities in ASP.NET MVC?

Use the syntax in ASP.NET MVC instead of using in .net framework 4.0.




Explain how to access Viewstate values of this page in the next page?

PreviousPage property is set to the page property of the nest page to access the viewstate value of the

page in the next page.

Page poster = this.PreviousPage;

Once that is done, a control can be found from the previous page and its state can be read.

Label posterLabel = poster.findControl("myLabel");

string lbl = posterLabel.Text;

What is difference between Viewbag and Viewdata in ASP.NET MVC?

The basic difference between ViewData and ViewBag is that in ViewData instead creating dynamic

properties we use properties of Model to transport the Model data in View and in ViewBag we can

create dynamic properties without using Model data.

What is Routing?

A route is a URL pattern that is mapped to a handler. The handler can be a physical file, such as an .aspx

file in a Web Forms application. Routing module is responsible for mapping incoming browser requests

to particular MVC controller actions.

Is it possible to combine ASP.NET webforms and ASP.MVC and develop a single web application?

Yes, it is possible to combine ASP.NET webforms and ASP.MVC and develop a single web application.

Is it possible to unit test an MVC application without running the controllers in an ASP.NET process?

Yes, all the features in an asp.net MVC application are interface based and hence mocking is much

easier. So, we don't have to run the controllers in an ASP.NET process for unit testing.

Is it possible to share a view across multiple controllers?

Yes, put the view into the shared folder. This will automatically make the view available across multiple

controllers.

What is the role of a controller in an MVC application?

The controller responds to user interactions, with the application, by selecting the action method to

execute and also selecting the view to render.

Where are the routing rules defined in an asp.net MVC application?

In Application_Start event in Global.asax




Name a few different return types of a controller action method?

The following are just a few return types of a controller action method. In general an action method can

return an instance of a any class that derives from ActionResult class.

1. ViewResult

2. JavaScriptResult

3. RedirectResult

4. ContentResult

5. JsonResult

What is the significance of NonActionAttribute?

In general, all public methods of a controller class are treated as action methods. If you want prevent

this default behavior, just decorate the public method with NonActionAttribute.

What is the significance of ASP.NET routing?

ASP.NET MVC uses ASP.NET routing, to map incoming browser requests to controller action methods.

ASP.NET Routing makes use of route table. Route table is created when your web application first starts.

The route table is present in the Global.asax file.

What are the 3 segments of the default route, that is present in an ASP.NET MVC application?

1st Segment - Controller Name

2nd Segment - Action Method Name

3rd Segment - Parameter that is passed to the action method

Example: http://dotnetcodes.com/Article/id/5

Controller Name = Article

Action Method Name = id

Parameter Id = 5

ASP.NET MVC application makes use of settings at 2 places for routing to work correctly. What are these

2 places?

1. Web.Config File: ASP.NET routing has to be enabled here.

2. Global.asax File: The Route table is created in the application Start event handler, of the

Global.asax file.

What is the advantage of using ASP.NET routing?

In an ASP.NET web application that does not make use of routing, an incoming browser request should

map to a physical file. If the file does not exist, we get page not found error.

An ASP.NET web application that does make use of routing makes use of URLs that do not have to map

to specific files in a Web site. Because the URL does not have to map to a file, you can use URLs that are

descriptive of the user's action and therefore are more easily understood by users.




What are the 3 things that are needed to specify a route?

1. URL Pattern - You can include placeholders in a URL pattern so that variable data can be passed

to the request handler without requiring a query string.

2. Handler - The handler can be a physical file such as an .aspx file or a controller class.

3. Name for the Route - Name is optional.

Is the following route definition a valid route definition?

{controller}{action}/{id}

No, the above definition is not a valid route definition, because there is no literal value or delimiter

between the placeholders. Therefore, routing cannot determine where to separate the value for the

controller placeholder from the value for the action placeholder.

What is the use of the following default route?

{resource}.axd/{*pathInfo}

This route definition, prevent requests for the Web resource files such as WebResource.axd or

ScriptResource.axd from being passed to a controller.

What is the difference between adding routes, to a webforms application and to an MVC application?

To add routes to a webforms application, we use MapPageRoute() method of the RouteCollection class,

where as to add routes to an MVC application we use MapRoute() method.

How do you handle variable number of segments in a route definition?

Use a route with a catch-all parameter. An example is shown below. * is referred to as catch-all

parameter.

controller/{action}/{*parametervalues}

What are the 2 ways of adding constraints to a route?

1. Use regular expressions

2. Use an object that implements IRouteConstraint interface

Give 2 examples for scenarios when routing is not applied?

1. A Physical File is found that Matches the URL Pattern - This default behavior can be overridden

by setting the RouteExistingFiles property of the RouteCollection object to true.

2. Routing Is Explicitly Disabled for a URL Pattern - Use the RouteCollection.Ignore() method to

prevent routing from handling certain requests.

What is the use of action filters in an MVC application?

Action Filters allow us to add pre-action and post-action behavior to controller action methods.




If I have multiple filters implanted, what is the order in which these filters get executed?

Authorization filters

Action filters

Response filters

Exception filters

Give an example for Authorization filters in an asp.net MVC application?

RequireHttpsAttribute

AuthorizeAttribute

Which filter executes first in an asp.net MVC application?

Authorization filter

What are the levels at which filters can be applied in an asp.net MVC application?

Action Method

Controller

Application

Is it possible to create a custom filter?

Yes

What filters are executed in the end?

Exception Filters

Is it possible to cancel filter execution?

Yes

What type of filter does OutputCacheAttribute class represents?

Result Filter

What are the 2 popular asp.net MVC view engines?

1. Razor

2. .aspx

What symbol would you use to denote, the start of a code block in razor views?

@

What symbol would you use to denote, the start of a code block in aspx views?

<%= %>

In razor syntax, what is the escape sequence character for @ symbol?




The escape sequence character for @ symbol, is another @ symbol

When using razor views, do you have to take any special steps to protect your asp.net MVC application

from cross site scripting (XSS) attacks?

No, by default content emitted using a @ block is automatically HTML encoded to protect from cross

site scripting (XSS) attacks.

When using aspx view engine, to have a consistent look and feel, across all pages of the application, we

can make use of asp.net master pages. What is asp.net master pages equivalent, when using razor

views?

To have a consistent look and feel when using razor views, we can make use of layout pages. Layout

pages, reside in the shared folder, and are named as _Layout.cshtml

What are sections?

Layout pages, can define sections, which can then be overridden by specific views making use of the

layout. Defining and overriding sections is optional.

What are the file extensions for razor views?

.cshtml - If the programming language is C#

.vbhtml - If the programming language is VB

How do you specify comments using razor syntax?

Razor syntax makes use of @* to indicate the beginning of a comment and *@ to indicate the end. An

example is shown below.

@* This is a Comment *@




Design Pattern

Command

Encapsulate a request as an object, thereby letting you parameterize clients with different requests,

queue or log requests, and support undoable operations.

/*the Command interface*/

public interface Command {

void execute();

}

/*the Invoker class*/

import java.util.List;

import java.util.ArrayList;

public class Switch {

private List<Command> history = new ArrayList<Command>();

public Switch() {

}

public void storeAndExecute(Command cmd) {

this.history.add(cmd); // optional

cmd.execute();

}

}

/*the Receiver class*/

public class Light {

public Light() {

}

public void turnOn() {

System.out.println("The light is on");

}

public void turnOff() {

System.out.println("The light is off");

}




}

/*the Command for turning on the light - ConcreteCommand #1*/

public class FlipUpCommand implements Command {

private Light theLight;

public FlipUpCommand(Light light) {

this.theLight = light;

}

public void execute(){

theLight.turnOn();

}

}

/*the Command for turning off the light - ConcreteCommand #2*/

public class FlipDownCommand implements Command {

private Light theLight;

public FlipDownCommand(Light light) {

this.theLight = light;

}

public void execute() {

theLight.turnOff();

}

}

/*The test class or client*/

public class PressSwitch {

public static void main(String[] args){

Light lamp = new Light();

Command switchUp = new FlipUpCommand(lamp);

Command switchDown = new FlipDownCommand(lamp);




Switch s = new Switch();

try {

if (args[0].equalsIgnoreCase("ON")) {

s.storeAndExecute(switchUp);

System.exit(0);

}

if (args[0].equalsIgnoreCase("OFF")) {

s.storeAndExecute(switchDown);

System.exit(0);

}

System.out.println("Argument \"ON\" or \"OFF\" is required.");

} catch (Exception e) {

System.out.println("Argument's required.");

}

}

}

Iterator

Provide a way to access the elements of an aggregate object sequentially without exposing its

underlying representation.

Null object

Avoid null references by providing a default object.

/* Null Object Pattern implementation:

*/

using System;

// Animal interface is the key to compatibility for Animal implementations

below.

interface IAnimal

{

void MakeSound();

}

// Dog is a real animal.

class Dog : IAnimal

{

public void MakeSound()

{

Console.WriteLine("Woof!");

}

}




// The Null Case: this NullAnimal class should be instantiated and used in

place of C# null keyword.

class NullAnimal : IAnimal

{

public void MakeSound()

{

// Purposefully provides no behaviour.

}

}

/* =========================

* Simplistic usage example in a Main entry point.

*/

static class Program

{

static void Main()

{

IAnimal dog = new Dog();

dog.MakeSound(); // outputs "Woof!"

/* Instead of using C# null, use a NullAnimal instance.

* This example is simplistic but conveys the idea that if a

NullAnimal instance is used then the program

* will never experience a .NET System.NullReferenceException at

runtime, unlike if C# null was used.

*/

IAnimal unknown = new NullAnimal(); //<< replaces: IAnimal unknown =

null;

unknown.MakeSound(); // outputs nothing, but does not throw a runtime

exception

}

}

Observer or Publish/subscribe

Define a one-to-many dependency between objects where a state change in one object results in all its

dependents being notified and updated automatically.

// Observer pattern -- Structural example

using System;

using System.Collections.Generic;

namespace DoFactory.GangOfFour.Observer.Structural




{

/// <summary>

/// MainApp startup class for Structural

/// Observer Design Pattern.

/// </summary>

class MainApp

{

/// <summary>

/// Entry point into console application.

/// </summary>

static void Main()

{

// Configure Observer pattern

ConcreteSubject s = new ConcreteSubject();

s.Attach(new ConcreteObserver(s, "X"));

s.Attach(new ConcreteObserver(s, "Y"));

s.Attach(new ConcreteObserver(s, "Z"));

// Change subject and notify observers

s.SubjectState = "ABC";

s.Notify();

// Wait for user

Console.ReadKey();

}

}

/// <summary>

/// The 'Subject' abstract class

/// </summary>

abstract class Subject

{




private List<Observer> _observers = new List<Observer>();

public void Attach(Observer observer)

{

_observers.Add(observer);

}

public void Detach(Observer observer)

{

_observers.Remove(observer);

}

public void Notify()

{

foreach (Observer o in _observers)

{

o.Update();

}

}

}

/// <summary>

/// The 'ConcreteSubject' class

/// </summary>

class ConcreteSubject : Subject

{

private string _subjectState;

// Gets or sets subject state

public string SubjectState

{

get { return _subjectState; }

set { _subjectState = value; }




}

}

/// <summary>

/// The 'Observer' abstract class

/// </summary>

abstract class Observer

{

public abstract void Update();

}

/// <summary>

/// The 'ConcreteObserver' class

/// </summary>

class ConcreteObserver : Observer

{

private string _name;

private string _observerState;

private ConcreteSubject _subject;

// Constructor

public ConcreteObserver(

ConcreteSubject subject, string name)

{

this._subject = subject;

this._name = name;

}

public override void Update()

{

_observerState = _subject.SubjectState;

Console.WriteLine("Observer {0}'s new state is {1}",

_name, _observerState);




}

// Gets or sets subject

public ConcreteSubject Subject

{

get { return _subject; }

set { _subject = value; }

}

}

}

Visitor

Represent an operation to be performed on the elements of an object structure. Visitor lets you define a

new operation without changing the classes of the elements on which it operates.

/ Visitor pattern -- Real World example

using System;

using System.Collections.Generic;

namespace DoFactory.GangOfFour.Visitor.RealWorld

{

/// <summary>

/// MainApp startup class for Real-World

/// Visitor Design Pattern.

/// </summary>

class MainApp

{

/// <summary>


/// </summary>

static void Main()

{

// Setup employee collection

Employees e = new Employees();

e.Attach(new Clerk());




e.Attach(new Director());

e.Attach(new President());

// Employees are 'visited'

e.Accept(new IncomeVisitor());

e.Accept(new VacationVisitor());

// Wait for user

Console.ReadKey();

}

}

/// <summary>

/// The 'Visitor' interface

/// </summary>

interface IVisitor

{

void Visit(Element element);

}

/// <summary>

/// A 'ConcreteVisitor' class

/// </summary>

class IncomeVisitor : IVisitor

{

public void Visit(Element element)

{

Employee employee = element as Employee;

// Provide 10% pay raise

employee.Income *= 1.10;

Console.WriteLine("{0} {1}'s new income: {2:C}",

employee.GetType().Name, employee.Name,




employee.Income);

}

}

/// <summary>

/// A 'ConcreteVisitor' class

/// </summary>

class VacationVisitor : IVisitor

{

public void Visit(Element element)

{

Employee employee = element as Employee;

// Provide 3 extra vacation days

Console.WriteLine("{0} {1}'s new vacation days: {2}",

employee.GetType().Name, employee.Name,

employee.VacationDays);

}

}

/// <summary>

/// The 'Element' abstract class

/// </summary>

abstract class Element

{

public abstract void Accept(IVisitor visitor);

}

/// <summary>

/// The 'ConcreteElement' class

/// </summary>

class Employee : Element

{




private string _name;

private double _income;

private int _vacationDays;

// Constructor

public Employee(string name, double income,

int vacationDays)

{

this._name = name;

this._income = income;

this._vacationDays = vacationDays;

}

// Gets or sets the name

public string Name

{

get { return _name; }

set { _name = value; }

}

// Gets or sets income

public double Income

{

get { return _income; }

set { _income = value; }

}

// Gets or sets number of vacation days

public int VacationDays

{

get { return _vacationDays; }

set { _vacationDays = value; }

}




public override void Accept(IVisitor visitor)

{

visitor.Visit(this);

}

}

/// <summary>

/// The 'ObjectStructure' class

/// </summary>

class Employees

{

private List<Employee> _employees = new List<Employee>();

public void Attach(Employee employee)

{

_employees.Add(employee);

}

public void Detach(Employee employee)

{

_employees.Remove(employee);

}

public void Accept(IVisitor visitor)

{

foreach (Employee e in _employees)

{

e.Accept(visitor);

}

Console.WriteLine();

}

}




// Three employee types

class Clerk : Employee

{

// Constructor

public Clerk()

: base("Hank", 25000.0, 14)

{

}

}

class Director : Employee

{

// Constructor

public Director()

: base("Elly", 35000.0, 16)

{

}

}

class President : Employee

{

// Constructor

public President()

: base("Dick", 45000.0, 21)

{

}

}

}




Singleton

Ensure a class has only one instance, and provide a global point of access to it. /// <summary> /// MainApp startup class for Structural /// Singleton Design Pattern. /// </summary> class MainApp { /// <summary> /// Entry point into console application. /// </summary> static void Main() { // Constructor is protected -- cannot use new Singleton s1 = Singleton.Instance(); Singleton s2 = Singleton.Instance(); // Test for same instance if (s1 == s2) { Console.WriteLine("Objects are the same instance"); } // Wait for user Console.ReadKey(); } } /// <summary> /// The 'Singleton' class /// </summary> class Singleton { private static Object _Lock = new Object(); private static Singleton _instance; // Constructor is 'protected' protected Singleton() { } public static Singleton Instance() { // Uses lazy initialization. // Note: this not thread safe. if (_instance == null) { lock (_Lock) { if(_instance == null) _instance = new Singleton(); } } return _instance; } }




Adapter or Wrapper or Translator

Convert the interface of a class into another interface clients expect. An adapter lets classes work

together that could not otherwise because of incompatible interfaces. The enterprise integration

pattern equivalent is the Translator.

using System;

namespace DoFactory.GangOfFour.Adapter.Structural

{

/// <summary>

/// MainApp startup class for Structural

/// Adapter Design Pattern.

/// </summary>

class MainApp

{

/// <summary>


/// </summary>

static void Main()

{

// Create adapter and place a request

Target target = new Adapter();

target.Request();

// Wait for user

Console.ReadKey();

}

}

/// <summary>

/// The 'Target' class

/// </summary>

class Target

{

public virtual void Request()




{

Console.WriteLine("Called Target Request()");

}

}

/// <summary>

/// The 'Adapter' class

/// </summary>

class Adapter : Target

{

private Adaptee _adaptee = new Adaptee();

public override void Request()

{

// Possibly do some other work

// and then call SpecificRequest

_adaptee.SpecificRequest();

}

}

/// <summary>

/// The 'Adaptee' class

/// </summary>

class Adaptee

{

public void SpecificRequest()

{

Console.WriteLine("Called SpecificRequest()");

}

}

}

Flyweight

Use sharing to support large numbers of similar objects efficiently.




Proxy

Provide a surrogate or placeholder for another object to control access to it.

interface Image {

void displayImage();

}

// on System A

class RealImage implements Image {

private String filename;

public RealImage(String filename) {

this.filename = filename;

loadImageFromDisk();

}

private void loadImageFromDisk() {

System.out.println("Loading " + filename);

}

public void displayImage() {

System.out.println("Displaying " + filename);

}

}

//on System B

class ProxyImage implements Image {

private String filename;

private RealImage image;

public ProxyImage(String filename) {

this.filename = filename;

}

public void displayImage() {

if (image == null) {

image = new RealImage(filename);

}

image.displayImage();

}

}

class ProxyExample {




public static void main(String[] args) {

Image image1 = new ProxyImage("HiRes_10MB_Photo1");

Image image2 = new ProxyImage("HiRes_10MB_Photo2");

image1.displayImage(); // loading necessary

image1.displayImage(); // loading unnecessary

image2.displayImage(); // loading necessary



}

}

Inversion of Control

Everybody has probably seen (or written) code like this before:

public class EmailService { public void SendMessage() { ... } } public class NotificationSystem { private EmailService svc; public NotificationSystem() { svc = new EmailService(); } public void InterestingEventHappened() { svc.SendMessage(); } }

Above NoticicationSystem has a dependency on EmailService.

The inversion of control (IoC) pattern is abstract; it says that one should move dependency creation out

of the consumer class, but it doesn’t talk about exactly how to achieve that. In the following sections,

we’ll explore two popular ways to apply the inversion of control pattern to achieve this responsibility

shift: service locator and dependency injection. public interface IMessagingService { void SendMessage(); } public class EmailService : IMessagingService { public void SendMessage() { ... } }




public class NotificationSystem { private IMessagingService svc; public NotificationSystem() { svc = new EmailService(); } public void InterestingEventHappened() { svc.SendMessage(); } }

Design Pattern: Service Locator

Now if you re-write NotificationSystem in terms of the strongly-typed service locator, it might look like

this:

Strongly typed service locator

public interface IServiceLocator { object GetService(Type serviceType); TService GetService<TService>(); } public static class ServiceLocatorExtensions { public static TService GetService<TService>(this IServiceLocator locator) { return (TService)locator.GetService(typeof(TService)); } } public class NotificationSystem { private IMessagingService svc; public NotificationSystem(IServiceLocator locator) { svc = locator.GetService<IMessagingService>(); } public void InterestingEventHappened() { svc.SendMessage(); } }

Design Pattern: Dependency Injection

The dependency injection (DI) pattern is another form of the inversion of control pattern, where in there

is no intermediary object like the service locator. Instead, components are written in a way that allows

their dependencies to be stated explicitly, usually by way of constructor parameters or property setters.

Constructor Injection




public class NotificationSystem { private IMessagingService svc; public NotificationSystem(IMessagingService service) { this.svc = service; } public void InterestingEventHappened() { svc.SendMessage(); } }

Property Injection public class NotificationSystem { public IMessagingService MessagingService { get; set; } public void InterestingEventHappened() { MessagingService.SendMessage(); } }

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