Friday, 25 December 2015

MVC Interview Questions and Answers

What are the features of MVC2?
ASP.NET MVC 2 was released in March 2010. Its main features are:
1)    Introduction of UI helpers with automatic scaffolding with customizable templates.
2)    Attribute-based model validation on both client and server.
3)    Strongly typed HTML helpers.
4)    Improved Visual Studio tooling.
5)    There were also lots of API enhancements and “pro” features, based on feedback from developers building a variety of applications on ASP.NET MVC 1, such as:
§  Support for partitioning large applications into areas.
§  Asynchronous controllers support.
§  Support for rendering subsections of a page/site using Html.RenderAction.
§  Lots of new helper functions, utilities, and API enhancements.

What are the features of MVC3?
ASP.NET MVC 3 shipped just 10 months after MVC 2 in Jan 2011. Some of the top features in MVC 3 included:
1)    The Razor view engine.
2)    Support for .NET 4 Data Annotations.
3)    Improved model validation.
4)    Greater control and flexibility with support for dependency resolution and global action filters.
5)    Better JavaScript support with unobtrusive JavaScript, jQuery Validation, and JSON binding.
6)    Use of NuGet to deliver software and manage dependencies throughout the platform.

What are the new features of MVC4?
Following are the top features of MVC4:
1)    ASP.NET Web API.
2)    Enhancements to default project templates.
3)    Mobile project template using jQuery Mobile.
4)    Display Modes.
5)    Task support for Asynchronous Controllers.
6)    Bundling and minification.

Advantages of MVC Framework?
1)    Provides a clean separation of concerns between UI (Presentation layer), model (Transfer objects/Domain Objects/Entities) and Business Logic (Controller).
2)    Easy to UNIT Test.
3)    Improved reusability of views/model. One can have multiple views which can point to the same model and vice versa.
4)    Improved structuring of the code.

What do you mean by Separation of Concerns?
As per Wikipedia, 'the process of breaking a computer program into distinct features that overlap in functionality as little as possible'. MVC design pattern aims to separate content from presentation and data-processing from content.

Where do we see Separation of Concerns in MVC?
Between the data-processing (Model) and the rest of the application.
When we talk about Views and Controllers, their ownership itself explains separation. The views are just the presentation form of an application; it does not have to know specifically about the requests coming from controller. The Model is independent of View and Controllers; it only holds business entities that can be passed to any View by the controller as required for exposing them to the end user.
The controller is independent of Views and Models, its sole purpose is to handle requests and pass it on as per the routes defined and as per the need of rendering views. Thus our business entities (model), business logic (controllers) and presentation logic (views) lie in logical/physical layers independent of each other.

What is Razor View Engine?
Razor is the first major update to render HTML in MVC3. Razor was designed specifically as view engine syntax. It has one main focus: code-focused templating for HTML generation. Here’s how that same markup would be generated using Razor:
@model MvcMusicStore.Models.Genre
ViewBag.Title = "Browse Albums";
<div class="genre">
<h3><em>@Model.Name</em> Albums</h3>
<ul id="album-list">

@foreach (var album in Model.Albums)
<a href="@Url.Action("Details", new { id = album.AlbumId })">
<img alt="@album.Title" src="@album.AlbumArtUrl" />

The Razor syntax is easier to type, and easier to read. Razor doesn’t have the XML-like heavy syntax of the Web Forms view engine.

What is Unobtrusive JavaScript?
Unobtrusive JavaScript is a general term that conveys a general philosophy, similar to the term REST (Representational State Transfer). The high-level description is that unobtrusive JavaScript doesn’t intermix JavaScript code in your page markup. For example, rather than hooking in via event attributes like onclick and onsubmit, the unobtrusive JavaScript attaches to elements by their ID or class, often based on the presence of other attributes (such as HTML5 data-attributes).
It’s got semantic meaning, and all of it — the tag structure, element attributes, and so on — should have a precise meaning. Strewing JavaScript gunk across the page to facilitate interaction (I’m looking at you, __doPostBack!) harms the content of the document.

What is JSON Binding?
MVC3 included JavaScript Object Notation (JSON) binding support via the new JsonValueProviderFactory, enabling the action methods to accept and model-bind data in JSON format. This is especially useful in advanced Ajax scenarios like client templates and data binding that need to post data back to the server.

What is Dependency Resolution?
MVC 3 introduced a new concept called a dependency resolver, which greatly simplified the use of dependency injection in your applications. This made it easier to decouple application components, making them more configurable and easier to test.
Support was added for the following scenarios:
·         Controllers (registering and injecting controller factories, injecting controllers)
·         Views (registering and injecting view engines, injecting dependencies into view pages)
·         Action filters (locating and injecting filters)
·         Model binders (registering and injecting)
·         Model validation providers (registering and injecting)
·         Model metadata providers (registering and injecting)
·         Value providers (registering and injecting)

What are Display Modes in MVC4?
Display modes use a convention-based approach to allow selecting different views based on the browser making the request. The default view engine first looks for views with names ending with .Mobile.cshtml when the browser’s user agent indicates a known mobile device. For example, if we have a generic view titled Index.cshtml and a mobile view titled Index.Mobile.cshtml, MVC 4 will automatically use the mobile view when viewed in a mobile browser.
Additionally, we can register your own custom device modes that will be based on your own custom criteria — all in just one code statement. For example, to register a WinPhone device mode that would serve views ending with .WinPhone.cshtml to Windows Phone devices, you’d use the following code in the Application_Start method of your Global.asax:
DisplayModeProvider.Instance.Modes.Insert(0, new DefaultDisplayMode("WinPhone")
ContextCondition = (context => context.GetOverriddenUserAgent().IndexOf
("Windows Phone OS", StringComparison.OrdinalIgnoreCase) >= 0)

What is AuthConfig.cs in MVC4?
AuthConfig.cs is used to configure security settings, including sites for OAuth login.

What is BundleConfig.cs in MVC4?
BundleConfig.cs in MVC4 is used to register bundles used by the bundling and minification system. Several bundles are added by default, including jQuery, jQueryUI, jQuery validation, Modernizer, and default CSS references.

What is FilterConfig.cs in MVC4?
This is used to register global MVC filters. The only filter registered by default is the HandleErrorAttribute, but this is a great place to put other filter registrations.

What is RouteConfig.cs in MVC4?
RouteConfig.cs holds the granddaddy of the MVC config statements, Route configuration.

What is WebApiConfig.cs in MVC4?
Used to register Web API routes, as well as set any additional Web API configuration settings.

What’s new in adding controller in MVC4 application?
Previously (in MVC3 and MVC2), the Visual Studio Add Controller menu item only displayed when we right-clicked on the Controllers folder. However, the use of the Controllers folder was purely for organization. (MVC will recognize any class that implements the IController interface as a Controller, regardless of its location in your application.) The MVC 4 Visual Studio tooling has been modified to display the Add Controller menu item for any folder in your MVC project. This allows us to organize your controllers however you would like, perhaps separating them into logical groups or separating MVC and Web API controllers.

What are the various types of Application Templates used to create an MVC application?
The various templates are as follows:
1)    The Internet Application template: This contains the beginnings of an MVC web application — enough so that you can run the application immediately after creating it and see a few pages. This template also includes some basic account management functions which run against the ASP.NET Membership.
2)    The Intranet Application template: The Intranet Application template was added as part of the ASP.NET MVC 3 Tools Update. It is similar to the Internet Application template, but the account management functions run against Windows accounts rather than the ASP.NET Membership system.
3)    The Basic template: This template is pretty minimal. It still has the basic folders, CSS, and MVC application infrastructure in place, but no more. Running an application created using the Empty template just gives you an error message.
Why use Basic template? The Basic template is intended for experienced MVC developers who want to set up and configure things exactly how they want them.
4)    The Empty template: The Basic template used to be called the Empty template, but developers complained that it wasn’t quite empty enough. With MVC 4, the previous Empty template was renamed Basic, and the new Empty template is about as empty as we can get. It has the assemblies and basic folder structure in place, but that’s about it.
5)    The Mobile Application template: The Mobile Application template is preconfigured with jQuery Mobile to jump-start creating a mobile only website. It includes mobile visual themes, a touch-optimized UI, and support for Ajax navigation.
6)    The Web API template: ASP.NET Web API is a framework for creating HTTP services. The Web API template is similar to the Internet Application template but is streamlined for Web API development. For instance, there is no user account management functionality, as Web API account management is often significantly different from standard MVC account management. Web API functionality is also available in the other MVC project templates, and even in non-MVC project types.

What are the default Top level directories created when adding MVC4 application?
Default Top level Directories are:
To put Controller classes that handle URL requests.
To put classes that represents and manipulates data and business objects.
To put UI template files that are responsible for rendering output like HTML.
To put JavaScript library files and scripts (.js).
To put images used in your site.
To put CSS and other site content, other than scripts and images.
To put filter code.
To store data files you want to read/write.
To put configuration code for features like Routing, Bundling, Web API.

What is namespace of ASP.NET MVC?
ASP.NET MVC namespaces as well as classes are located in assembly System.Web.Mvc.

What is System.Web.Mvc namespace?
This 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.

What is System.Web.Mvc.Ajax namespace?
System.Web.Mvc.Ajax namespace contains classes that support Ajax scripting in an ASP.NET MVC application. The namespace includes support for Ajax scripts and Ajax option settings as well.

What is System.Web.Mvc.Async namespace?
System.Web.Mvc.Async namespace contains classes and interfaces that support asynchronous actions in an ASP.NET MVC application.

What is System.Web.Mvc.Html namespace?
System.Web.Mvc.Html namespace contains classes that help render HTML controls in an MVC application. This namespace includes classes that support forms, input controls, links, partial views, and validation.

What are the roles and similarities between ViewData and ViewBag?
1)    Maintains data when moving from controller to view.
2)    Passes data from controller to respective view.
3)    Their value becomes null when any redirection occurs, because their role is to provide a way to communicate between controllers and views. It’s a communication mechanism within the server call.

What are the differences between ViewData and ViewBag?
·      ViewData is a dictionary of objects that is derived from ViewDataDictionary class and accessible using string as keys.
·      ViewBag is a dynamic property that takes advantage of the new dynamic features in C# 4.0.
·      ViewData requires typecasting for complex data type and checks for null values to avoid error.
·      ViewBag doesn’t require typecasting for complex data type.
NOTE: Although there might not be a technical advantage to choosing one format over the other, there are some critical differences to be aware of between the two syntaxes.
One obvious difference is that ViewBag works only when the key being accessed is a valid C# identifier. For example, if you place a value in ViewData["KeyWith Spaces"], you can’t access that value using ViewBag because the code won’t compile.
Another key issue to be aware of is that dynamic values cannot be passed in as parameters to extension methods. The C# compiler must know the real type of every parameter at compile time in order for it to choose the correct extension method.
If any parameter is dynamic, compilation will fail. For example, this code will always fail: @Html.TextBox("name", ViewBag.Name). To work around this, either use ViewData["Name"] or cast the value to a specific type: (string) ViewBag.Name.

What is TempData?
TempData is a dictionary derived from the TempDataDictionary class and stored in short lives session. It is a string key and object value.
It keeps the information for the time of an HTTP Request. This means only from one page to another. It helps to maintain data when we move from one controller to another controller or from one action to other action. In other words, when we redirect Tempdata helps to maintain data between those redirects. It internally uses session variables. Temp data use during the current and subsequent request only means it is used when we are sure that the next request will be redirecting to next view. It requires typecasting for complex data type and checks for null values to avoid error. Generally it is used to store only one time messages like error messages, validation messages.

What are Scaffold templates?
These templates use the Visual Studio T4 templating system to generate a view based on the model type selected. Scaffolding in ASP.NET MVC can generate the boilerplate code we need for create, read, update, and delete (CRUD) functionality in an application. The scaffolding templates can examine the type definition for, and then generate a controller and the controller’s associated views. The scaffolding knows how to name controllers, how to name views, and what code needs to go in each component, and where to place all these pieces in the project for the application to work.

What are the types of Scaffolding Templates?
Creates empty view. Only the model type is specified using the model syntax.
Creates a view with a form for creating new instances of the model. Generates a label and input field for each property of the model type.
Creates a view with a form for deleting existing instances of the model. Displays a label and the current value for each property of the model.
Creates a view that displays a label and the value for each property of the model type.
Creates a view with a form for editing existing instances of the model. Generates a label and input field for each property of the model type.
Creates a view with a table of model instances. Generates a column for each property of the model type. Make sure to pass an IEnumerable<YourModelType> to this view from your action method. The view also contains links to actions for performing the create/edit/delete operation.

Explain Repository Pattern in ASP.NET MVC?
In simple terms, a repository basically works as a mediator between our business logic layer and our data access layer of the application. Sometimes, it would be troublesome to expose the data access mechanism directly to business logic layer, it may result in redundant code for accessing data for similar entities or it may result in a code that is hard to test or understand. To overcome these kinds of issues, and to write an Interface driven and test driven code to access data, we use Repository Pattern. The repository makes queries to the data source for the data, thereafter maps the data from the data source to a business entity/domain object, finally and persists the changes in the business entity to the data source. According to MSDN, a repository separates the business logic from the interactions with the underlying data source or Web service. The separation between the data and business tiers has three benefits:
1)    It centralizes the data logic or Web service access logic.
2)    It provides a substitution point for the unit tests.
3)    It provides a flexible architecture that can be adapted as the overall design of the application evolves.
In Repository, we write our whole business logic of CRUD operations with the help of Entity Framework classes, that will not only result in meaningful test driven code but will also reduce our controller code of accessing data.

How can you call a JavaScript function on the change of Dropdown List in MVC?
<script type="text/javascript">
            function selectedIndexChanged() {

Invoke the method:
@Html.DropDownListFor(x => x.SelectedProduct,
new SelectList(Model.Users, "Value", "Text"),
"Please Select a User", new { id = "ddlUsers",
onchange="selectedIndexChanged()" })

What are Layouts in ASP.NET MVC Razor?
Layouts in Razor help maintain a consistent look and feel across multiple views within our application. As compared to Web Forms, layouts serve the same purpose as master pages, but offer both a simpler syntax and greater flexibility.
We can use a layout to define a common template for your site (or just part of it). This template contains one or more placeholders that the other views in your application provide content for. In some ways, it’s like an abstract base class for your views.
E.g. declared at the top of view as:
       Layout = "~/Views/Shared/SiteLayout.cshtml";

What is ViewStart?
For group of views that all use the same layout, this can get a bit redundant and harder to maintain.
The _ViewStart.cshtml page can be used to remove this redundancy. The code within this file is executed before the code in any view placed in the same directory. This file is also recursively applied to any view within a subdirectory.
When we create a default ASP.NET MVC project, we find there is already a _ViewStart .cshtml file in the Viewsdirectory. It specifies a default layout:
Layout = "~/Views/Shared/_Layout.cshtml";
Because this code runs before any view, a view can override the Layout property and choose a different one. If a set of views shares common settings, the _ViewStart.cshtml file is a useful place to consolidate these common view settings. If any view needs to override any of the common settings, the view can set those values to another value.

What are HTML Helpers?
HTML helpers are methods we can invoke on the HTML property of a view. We also have access to URL helpers (via the Url property), and AJAX helpers (via the Ajax property). All these helpers have the same goal: to make views easy to author. The URL helper is also available from within the controller. Most of the helpers, particularly the HTML helpers, output HTML markup. For example, the BeginForm helper is a helper we can use to build a robust form tag for our search form, but without using lines and lines of code:
@using (Html.BeginForm("Search", "Home", FormMethod.Get)) {
<input type="text" name="q" />
<input type="submit" value="Search" />

What is Html.ValidationSummary?
The ValidationSummary helper displays an unordered list of all validation errors in the ModelState dictionary. The Boolean parameter you are using (with a value of true) is telling the helper to exclude property-level errors. In other words, you are telling the summary to display only the errors in ModelState associated with the model itself, and exclude any errors associated with a specific model property. We will be displaying property-level errors separately. Assume you have the following code somewhere in the controller action rendering the edit view:
ModelState.AddModelError("", "This is all wrong!");
ModelState.AddModelError("Title", "What a terrible name!");
The first error is a model-level error, because you didn’t provide a key (or provided an empty key) to associate the error with a specific property. The second error you associated with the Title property, so in your view it will not display in the validation summary area (unless you remove the parameter to the helper method, or change the value to false). In this scenario, the helper renders the following HTML:
<div class="validation-summary-errors">
<li>This is all wrong!</li>
Other overloads of the ValidationSummary helper enable you to provide header text and set specific HTML attributes.
NOTE: By convention, the ValidationSummary helper renders the CSS class validation-summary-errors along with any specific CSS classes you provide. The default MVC project template includes some styling to display these items in red, which you can change in styles.css.

What is Html.Partial?
The Partial helper renders a partial view into a string. Typically, a partial view contains reusable markup you want to render from inside multiple different views. Partial has four overloads:
public void Partial(string partialViewName);
public void Partial(string partialViewName, object model);
public void Partial(string partialViewName, ViewDataDictionary viewData);
public void Partial(string partialViewName, object model,
ViewDataDictionary viewData);

What is Html.RenderPartial?
The RenderPartial helper is similar to Partial, but RenderPartial writes directly to the response output stream instead of returning a string. For this reason, you must place RenderPartial inside a code block instead of a code expression. To illustrate, the following two lines of code render the same output to the output stream:
@{Html.RenderPartial("AlbumDisplay"); }

If they are the same, then which one to use?
In general, you should prefer Partial to RenderPartial because Partial is more convenient (you don’t have to wrap the call in a code block with curly braces). However, RenderPartial may result in better performance because it writes directly to the response stream, although it would require a lot of use (either high site traffic or repeated calls in a loop) before the difference would be noticeable.

How do you return a partial view from controller?
return PartialView(options); //options could be Model or View name

What are different ways of returning a View?
There are different ways for returning/rendering a view in MVC Razor. E.g. return View(), return RedirectToAction(), return Redirect() and return RedirectToRoute().

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