MVC interview questions

What are the 3 main components of an ASP.NET MVC application?
1. M - Model
2. V - View
3. C - Controller

In which assembly is the MVC framework defined?
System.Web.Mvc

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.

What does Model, View and Controller represent in an MVC application?
Model: Model represents the application data domain. In short the applications business logic is contained with in the model.

View: Views represent the user interface, with which the end users interact. In short the all the user interface logic is contained with in the UI.

Controller: Controller is the component that responds to user actions. Based on the user actions, the respective controller, work with the model, and selects a view to render that displays the user interface. The user input logic is contained with in the controller.

What is the greatest advantage of using asp.net mvc over asp.net webforms?
It is difficult to unit test UI with webforms, where views in mvc can be very easily unit tested.

Which approach provides better support for test driven development - ASP.NET MVC or ASP.NET Webforms?
ASP.NET MVC

What are the advantages of ASP.NET MVC?
1. Extensive support for TDD. With asp.net MVC, views can also be very easily unit tested.
2. Complex applications can be easily managed
3. Seperation of concerns. Different aspects of the application can be divided into Model, View and Controller.
4. ASP.NET MVC views are light weight, as they donot use viewstate.

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 alse 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 behaviour, 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://pragimtech.com/Customer/Details/5
Controller Name = Customer
Action Method Name = Details
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 adavantage 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 behaviour can be overriden 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 impleted, what is the order in which these filters get executed?
1. Authorization filters
2. Action filters
3. Response filters
4. Exception filters

What are the different types of filters, in an asp.net mvc application?
1. Authorization filters
2. Action filters
3. Result filters
4. Exception filters

Give an example for Authorization filters in an asp.net mvc application?
1. RequireHttpsAttribute
2. 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?
1. Action Method
2. Controller
3. Application
[b]Is it possible to create a custom filter?[/b]
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 proctect 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 overriden by specific views making use of the layout. Defining and overriding sections is optional.

What are the file extensions for razor views?
1. .cshtml - If the programming lanugaue is C#
2. .vbhtml - If the programming lanugaue is VB

How do you specify comments using razor syntax?
Razor syntax makes use of @* to indicate the begining of a comment and *@ to indicate the end. An example is shown below.
@* This is a Comment *@

reference: http://www.dotnetobject.com/Thread-MVC-Interview-Questions-Answers

Choosing Between MVC and MVP Patterns in ASP.NET

Introduction

Lately, ASP.NET developers have been paying increasing attention to the architectural aspect of their applications. However, little effort usually is done to choose the right architectural solution. Developers often make a blind choice in favour of the Model-View-Controller pattern and, specifically, ASP.NET MVC framework, disregarding other possible solutions.

Nevertheless, alternative architectural solutions, such as Model-View-Presenter and corresponding frameworks (MVC#, for instance) do prove themselves more useful than MVC in many situations. That is why ASP.NET developers and architects should be aware of all advantages of MVP pattern over MVC and vice versa to choose the appropriate pattern to be used in a specific application. This article provides guidelines for ASP.NET developers on choosing the right pattern among MVC and MVP, concerning all major differences between them.

Choice criteria

1. UI library used

Most ASP.NET user interface controls rely on the server-side event model to process user gestures. When a user clicks some menu item or a button on a web page, a server-side event gets generated and then handled on default by a View class (Web form class). Thus, the View is the best place to receive user input for most ASP.NET UI libraries, both standard and third-party (such as DevExpress or Telerik Web controls).

However, as seen from the picture below, the Model-View-Controller pattern bypasses the standard ASP.NET request processing scheme, because the incoming gestures in MVC are received by the Controller. Moreover, the form of user requests in the ASP.NET MVC framework (which is based on a URI pattern) makes it difficult to adapt this framework to use with the conventional ASP.NET server-side event model. And, although there are a number of UI libraries compatible with MVC pattern (for example, the Yahoo UI library), generally MVC is not fully suitable for most ASP.NET UI libraries.

The Model-View-Presenter pattern, on the contrary, assumes the View to receive user gestures and then to delegate processing to the Controller. Such a scheme comfortably fits most ASP.NET UI libraries.

To sum up, a developer should consider whether the desired UI library relies on the standard ASP.NET server-side event model. If it does (which is most likely), MVP would probably be a better choice.

2. Controller-View linking

According to the Model-View-Presenter pattern, a Controller has a constant link to the associated View object. This allows a Controller to access its View at any moment, either by getting or setting some View properties.

The Model-View-Controller, on the other hand, provides limited capabilities for communication between the Controller and the View. MVC requires passing all data to the view in a single call, such as Render("OrdersView", ordersParam1, or ordersParam2).

Thus, if an application needs extensive communication between Controller and View objects, MVP is more preferable than MVC.

3. Portability to other UI platforms

Many applications are initially designed to work under tbe Windows platform, and later they get ported to the web environment. Other applications are constructed to operate under multiple UI front-ends from the very beginning. Anyway, portability to other presentation platforms is a question of great importance for numerous systems.

And again, MVP shows itself as a better choice because it is compatible with various UI platforms. For example, MVC# Framework currently supports Windows Forms and ASP.NET Web Forms technologies, and Silverlight with WPF is on the agenda. The MVC pattern, quite the contrary, is good mainly for web applications and hardly fits other presentations.

Therefore, if an application needs or later will need support for multiple GUI platforms, MVP would be the right solution.

4. Tasks support

The Task concept belongs neither to MVC nor to MVP paradigms. However, it is included in some MVC/MVP frameworks for its usefulness. Task is a set of views that a user traverses to fulfil some job. For example, an airline ticket booking task may consist of two views: one for choosing the flight, the other for entering personal information. Tasks often correspond to certain use cases of the system: There may be "Login to the system" and "Process order" use cases and tasks of the same names. Finally, a task may be associated with a state machine or a workflow: For example, a "Process order" task could be implemented with the "Process order" workflow in WWF.

A developer should consider whether tasks can help him build his application and accordingly choose a framework with support for tasks (such as MVC# or Ingenious MVC). Generally, the more complicated an application is, the more likely it could make use of the Task concept.

Summary

You have considered the main differences between two popular architectural patterns: Model-View-Controller and Model-View-Presenter, and have learned the reasons for choosing one of them. The article shows that MVP could be a better choice for ASP.NET applications in many scenarios, and developers should certainly consider MVP frameworks as good alternatives to existing MVC solutions.

http://www.codeguru.com/csharp/.net/net_general/patterns/article.php/c15173

MVC or MVP Pattern – Whats the difference?

Over the years I have mentored many developers on using design patterns and best practices. One question that keeps coming up over and over again is: What are the differences between the Model View Controller (MVC) and Model View Presenter (MVP) patterns? Surprisingly the answer is more complex than what you would suspect. Part of reasons I think many developers shy away from using either pattern is the confusion over the differences.

Before we dig into the differences let’s examine how the patterns work and the key benefits to using either one. Both (MVC & MVP) patterns have been use for several years and address a key OO principal namely separation of concerns between the UI and the business layers. There are a number of frameworks is use today that based on these patterns including: JAVA Struts, ROR, Microsoft Smart Client Software Factory (CAB), Microsoft Web Client Software Factory, and the recently announced ASP.Net MVC framework.

Model View Controller (MVC) Pattern

The MVC pattern is a UI presentation pattern that focuses on separating the UI (View) from its business layer (Model). The pattern separates responsibilities across three components: the view is responsible for rending UI elements, the controller is responsible for responding to UI actions, and the model is responsible for business behaviors and state management. In most implementation all three components can directly interact with each other and in some implementations the controller is responsible for determining which view to display (Front Controller Pattern),

Model View Presenter (MVP) Pattern

 

The MVP pattern is a UI presentation pattern based on the concepts of the MVC pattern. The pattern separates responsibilities across four components: the view is responsible for rending UI elements, the view interface is used to loosely couple the presenter from its view, the presenter is responsible for interacting between the view/model, and the model is responsible for business behaviors and state management. In some implementations the presenter interacts with a service (controller) layer to retrieve/persist the model. The view interface and service layer are commonly used to make writing unit tests for the presenter and the model easier.

Key Benefits

Before using any pattern a developers needs to consider the pros and cons of using it. There are a number of key benefits to using either the MVC or MVP pattern (See list below). But, there also a few draw backs to consider. The biggest drawbacks are additional complexity and learning curve. While the patterns may not be appropriate for simple solutions; advance solutions can greatly benefit from using the pattern. I’m my experience a have seen a few solutions eliminate a large amount of complexity but being re-factored to use either pattern.

 

·         Loose coupling – The presenter/controller are an intermediary between the UI code and the model. This allows the view and the model to evolve independently of each other.

·         Clear separation of concerns/responsibility

o    UI (Form or Page) – Responsible for rending UI elements

o    Presenter/controller – Responsible for reacting to UI events and interacts with the model

o    Model – Responsible for business behaviors and state management

·         Test Driven – By isolating each major component (UI, Presenter/controller, and model) it is easier to write unit tests. This is especially true when using the MVP pattern which only interacts with the view using an interface.

·         Code Reuse – By using a separation of concerns/responsible design approach you will increase code reuse. This is especially true when using a full blown domain model and keeping all the business/state management logic where it belongs.

·         Hide Data Access – Using these patterns forces you to put the data access code where it belongs in a data access layer. There a number of other patterns that typical works with the MVP/MVC pattern for data access. Two of the most common ones are repository and unit of work. (See Martin Fowler – Patterns of Enterprise Application Architecture for more details)

·         Flexibility/Adaptable – By isolating most of your code into the presenter/controller and model components your code base is more adaptable to change. For example consider how much UI and data access technologies have changed over the years and the number of choices we have available today. A properly design solution using MVC or MVP can support multi UI and data access technologies at the same time.

Key Differences

So what really are the differences between the MVC and MVP pattern. Actually there are not a whole lot of differences between them. Both patterns focus on separating responsibility across multi components and promote loosely coupling the UI (View) from the business layer (Model).  The major differences are how the pattern is implemented and in some advanced scenarios you need both presenters and controllers.

 

Here are the key differences between the patterns:

 

·         MVP Pattern

o    View is more loosely coupled to the model. The presenter is responsible for binding the model to the view.

o    Easier to unit test because interaction with the view is through an interface

o    Usually view to presenter map one to one. Complex views may have multi presenters.

 

·         MVC Pattern

o    Controller are based on behaviors and can be shared across views

o    Can be responsible for determining which view to display (Front Controller Pattern)

 

Hopefully you found this post interesting and it helped clarify the differences between the MVC and MVP pattern. If not, do not be discouraged patterns are powerful tools that can be hard to use sometimes. One thing to remember is that a pattern is a blue print and not an out of the box solutions. Developers should use them as a guide and modify the implementation according to their problem domain.