Top 10 ASP.NET MVC Interview Questions

1. Explain MVC (Model-View-Controller) in general?

MVC (Model-View-Controller) is an architectural software pattern that basically decouples various components of a web application. By using MVC pattern, we can develop applications that are more flexible to changes without affecting the other components of our application.

•  “Model”, is basically domain data.
•  “View”, is user interface to render domain data.
•  “Controller”, translates user actions into appropriate operations performed on model.

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2. What is ASP.NET MVC?

ASP.NET MVC is a web development framework from Microsoft that is based on MVC (Model-View-Controller) architectural design pattern. Microsoft has streamlined the development of MVC based applications using ASP.NET MVC framework.
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3. Difference between ASP.NET MVC and ASP.NET WebForms?

ASP.NET Web Forms uses Page controller pattern approach for rendering layout, whereas ASP.NET MVC uses Front controller approach. In case of Page controller approach, every page has its own controller i.e. code-behind file that processes the request. On the other hand, in ASP.NET MVC, a common controller for all pages processes the requests.
Follow the link for the difference between the ASP.NET MVC and ASP.NET WebForms.
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4. What are the Core features of ASP.NET MVC?

Core features of ASP.NET MVC framework are:

• Clear separation of application concerns (Presentation and Business Logic). It reduces complexity that makes it ideal for large scale applications where multiple teams are working.
• It’s an extensible as well as pluggable framework. We can plug components and further customize them easily.
• It provides extensive support for URL Routing that helps to make friendly URLs (means friendly for human as well as Search Engines).
• It supports for Test Driven Development (TDD) approach. In ASP.NET WebForms, testing support is dependent on Web Server but ASP.NET MVC makes it independent of Web Server, database or any other classes.
• Support for existing ASP.NET features like membership and roles, authentication and authorization, provider model and caching etc.

Follow for detailed understanding of above mentioned core features.

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5. Can you please explain the request flow in ASP.NET MVC framework?

Request flow for ASP.NET MVC framework is as follows:
Request hits the controller coming from client. Controller plays its role and decides which model to use in order to serve the request. Further passing that model to view which then transforms the model and generate an appropriate response that is rendered to client.

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6. What is Routing in ASP.NET MVC?

In case of a typical ASP.NET application, incoming requests are mapped to physical files such as .aspx file. On the other hand, ASP.NET MVC framework uses friendly URLs that more easily describe user’s action but not mapped to physical files. Let’s see below URLs for both ASP.NET and ASP.NET MVC.

//ASP.NET  approach – Pointing to physical files (Student.aspx)
//Displaying all students
http://locahost:XXXX/Student.aspx

//Displaying a student by Id = 5
http://locahost:XXXX/Student.aspx?Id=5

//ASP.NET MVC approach – Pointing to Controller i.e. Student
//Displaying all students
http://locahost:XXXX/Student

//Displaying student by Id = 5
http://locahost:XXXX/Student/5/

ASP.NET MVC framework uses a routing engine, that maps URLs to controller classes. We can define routing rules for the engine, so that it can map incoming request URLs to appropriate controller. Practically, when a user types a URL in a browser window for an ASP.NET MVC application and presses “go” button, routing engine uses routing rules that are defined in Global.asax file in order to parse the URL and find out the path of corresponding controller. You can find complete details of ASP.NET MVC Routing here.
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7. What is the difference between ViewData, ViewBag and TempData?

In order to pass data from controller to view and in next subsequent request, ASP.NET MVC framework provides different options i.e. ViewData, ViewBag and TempData.

Both ViewBag and ViewData are used to to communicate between controller and corresponding view. But this communication is only for server call, it becomes null if redirect occurs. So, in short, its a mechanism to maintain state between controller and corresponding view. ViewData is a dictionary object while ViewBagis a dynamic property (a new C# 4.0 feature). ViewData being a dictionary object is accessible using strings as keys and also requires typecasting for complex types. On the other hand, ViewBag doesn’t have typecasting and null checks.

TempData is also a dictionary object that stays for the time of an HTTP Request. So, Tempdata can be used to maintain data between redirects i.e from one controller to the other controller.

You can easily find detailed examples for implementation of ViewBag, ViewData and TempData here.
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8. What are Action Methods in ASP.NET MVC?

As I already explained about request flow in ASP.NET MVC framework that request coming from client hits controller first. Actually MVC application determines the corresponding controller by using routing rules defined in Global.asax. And controllers have specific methods for each user actions. Each request coming to controller is for a specific Action Method. The following code sample, “ShowBook” is an example of an Action Method.

  public ViewResult ShowBook(int id)
  {
           var computerBook = db.Books.Where(p => P.BookID == id).First();
           return View(computerBook);
  }

Action methods perform certain operation using Model and return result back to View. As in above example,ShowBook is an action method that takes an Id as input, fetch specific book data and returns back to Viewas ViewResult. In ASP.NET MVC, we have many built-in ActionResults type:

• ViewResult
• PartialViewResult
• RedirectResult
• RedirectToRouteResult
• ContentResult
• JsonResult
• EmptyResult
• and many more….

For a complete list of available ActionResults types with Helper methods, please click here.

Important Note: All public methods of a Controller in ASP.NET MVC framework are considered to be Action Methods by default. If we want our controller to have a Non Action Method, we need to explicitly mark it withNonAction attribute as follows:

[NonAction]
public void MyNonActionMethod() { ….. }

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9.Explain the role of Model in ASP.NET MVC?

One of the core feature of ASP.NET MVC is that it separates the input and UI logic from business logic. Role of Model in ASP.NET MVC is to contain all application logic including validation, business and data access logic except view i.e. input and controller i.e UI logic.
Model is normally responsible for accessing data from some persistent medium like database and manipulate it, so you can expect that interviewer can ask questions on database access topics here along with ASP.NET MVC Interview Questions.
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10.What are Action Filters in ASP.NET MVC?

If we need to apply some specific logic before or after action methods, we use action filters. We can apply these action filters to a controller or a specific controller action. Action filters are basically custom classes that provide a mean for adding pre-action or post-action behavior to controller actions.
For example,

• Authorize filter can be used to restrict access to a specific user or a role.
• OutputCache filter can cache the output of a controller action for a specific duration.

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More Interview Questions on ASP.NET MVC

What is a ViewEngine in ASP.NET MVC?

“View Engine in ASP.NET MVC is used to translate our views to HTML and then render to browser.”
There are few View Engines available for ASP.NET MVC but commonly used View Engines are Razor, Web Forms/ASPX, NHaml and Spark etc. Most of the developers are familiar with Web Forms View Engine (ASPX) and Razor View Engine.

• Web Form View Engine was with ASP.NET MVC since beginning.
• Razor View Engine was introduced later in MVC3.
• NHaml is an open source view engine since 2007.
• Spark is also an open source since 2008.

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What is the difference between Razor View Engine and ASPX View Engine?

I have written a separate detailed blog post to understand the  Difference between ASPX View Engine and Razor View Engine. You can follow the link to get detailed step by step description  here. Most important differences are listed below:

ASPX View Engine	Razor View Engine
WebForms View Engine uses namespace “System.Web.Mvc.WebFormViewEngine”.	“System.Web.Razor” is the namespace for Razor View Engine.
Comparatively fast.	A little bit slower than ASPX View Engine.
Nothing like Test Driven Development	Good support for Test Driven Development.
Syntax for ASPX View Engine is inherited from Web Forms pages as: <%= employee.FullName %>	Syntax for Razor View Engine is comparatively less and clean. @employee.FullName

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What is a ViewModel in ASP.NET MVC?

A ViewModel basically acts as a single model object for multiple domain models, facilitating to have only one optimized object for View to render. Below diagram clearly express the idea of ViewModel in ASP.NET MVC:

There are multiple scenarios where using ViewModel becomes obvious choice. For example:

• Parent-Child View Scenario
• Reports where often aggregated data required
• Model object having lookup data
• Dashboards displaying data from multiple sources

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What are ASP.NET MVC HtmlHelpers?

ASP.NET MVC HtmlHelpers fulfills almost the same purpose as that of ASP.NET Web From Controls. For imlementation point of view, HtmlHelper basically is a method that returns a string ( i.e. an HTML string to render HTML tags). So, in ASP.NET MVC we have HtmlHelpers for links, Images and for Html form elements etc. as follows:

@Html.ActionLink(“WebDev Consulting Company Profile”, “CompanyInfo”) will render:
<a href=”/Site/CompanyInfo”>WebDev Consulting Company Profile</a>

and

@Html.TextBox(“strEmployeeName”) renders:
<input id=”strEmployeeName” name=”strEmployeeName” type=”text” value=”” />

For a complete reference to Standard ASP.NET MVC Html Helpers, Click Here.

Note: Html Helpers are comparatively lightweight because these don’t have ViewState and event model as for ASP.NET Web Form Controls.

We can also create our Custom Html Helpers to fulfill specific application requirements. There are 2 ways to create custom HtmlHelpers as follows:
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What is Bootstrap in MVC5?

Bootstrap (a front-end framework) is an open source collection of tools that contains HTML and CSS-based design templates along with Javascript to create a responsive design for web applications. Bootstrap provides a base collection including layouts, base CSS, JavaScript widgets, customizable components and plugins.

Project Template in ASP.NET MVC5 is now using bootstrap that enhances look and feel with easy customization. Bootstrap version 3 is added to ASP.NET MVC5 template as shown below:
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Kindly explain Attribute Routing in ASP.NET MVC5?

We already have discussed about Routing in Question#6 that in ASP.NET MVC, we use friendly URLs that are mapped to controller’s actions instead of physical files as in case of ASP.NET WebForms. Now in ASP.NET MVC5, we can use attributes to define routes giving better control over the URIs.

We can easily define routes with Controller’s action methods as follows:

Note: Remember that conventional routing approach is not discarded, it’s still there and fully functional. Also, we can use both routing techniques in a same application. Click here for more details on Attribute Routing.