Interview Questions - Asp.Net MVC

What is MVC?

MVC is an architectural pattern which separates the application into three main components 'Model', 'View' and 'Controller'.
Model represent the application state. There are many ways to organize the Model in app 'Domain model', 'View Mode', 'Binding Model', 'API Model' and 'Persistence Model'.

View is responsible for present content through the user interface. We use the 'Razor View Engine' to embed .Net code in HTML markup.

Controllers are the components which handle user interaction, work with the Model and select a View to render.

What are the Advantages of using Asp.Net MVC?
Why MVC over WebForms?

The ASP.NET MVC framework offers the following advantages:
Separation Of Concerns: It makes it easier to manage complexity by dividing an application into the model, the view, and the controller.

Lightweight: It doesn’t use View State and thus reduces the bandwidth of the requests to an extent.

Test Driven Development: It provides better support for test-driven development (TDD).

Full features of ASP.NET: One of the key advantages of using ASP.NET MVC is that it is built on top of ASP.NET framework and hence most of the features of the ASP.NET like membership providers, roles, etc can still be used.

Explain MVC application life cycle?

- HttpApplication - If first request then it perform common tasks such as register routes, bundles, and filters.

- Routing - Match request to define route and call MvcHanlder and stored route data in it.

- Controller - MvcHandler uses the ControllerFactory to get the Controller instance.

- Action - Once the controller has been instantiated, Controller's ActionInvoker determines which specific action to invoke on the controller.

- Result Execution - The action method receives user input, prepares the appropriate response data, and then executes the result by returning a result type. The result type can be ViewResult, RedirectToRouteResult, RedirectResult, ContentResult, JsonResult, FileResult, and EmptyResult.

- View Engine : The view engine is responsible for creating HTML from view, which could be a mix-up of HTMl and programming language.

To understand Asp.Net MVC life cycle better, you can refer below links

https://docs.microsoft.com/en-gb/aspnet/mvc/overview/getting-started/lifecycle-of-an-aspnet-mvc-5-application/_static/lifecycle-of-an-aspnet-mvc-5-application1.pdf

http://blog.thedigitalgroup.com/chetanv/2015/06/30/a-detailed-walkthrough-of-asp-net-mvc-request-life-cycle/

https://www.codeproject.com/Articles/741228/MVC-Application-Lifecycle

What is ViewData, ViewBag, TempData and Session in Asp.Net MVC?

ViewData
- ViewData is a dictionary object that is derived from ViewDataDictionary class.
public ViewDataDictionary ViewData{ get; set; }
- ViewData is used to pass data from controller to corresponding view.
- Its life lies only during the current request.
- If redirection occurs then its value becomes null.
- It’s required typecasting for getting data and check for null values to avoid error.

ViewBag
- ViewBag is a dynamic property that takes advantage of the new dynamic features in C# 4.0.
public dynamic ViewBag{ get;}
- Basically, it is a wrapper around the ViewData and also used to pass data from controller to the corresponding view.
- Its life also lies only during the current request.
- If redirection occurs then its value becomes null.
- It doesn’t require typecasting for getting data.

TempData
- TempData is a dictionary object that is derived from TempDataDictionary class and stored in short lives session.
public TempDataDictionary TempData{get;set;}
- TempData is used to pass data from current request to subsequent request (means redirecting from one page to another).
- Its life is very short and lies only till the target view is fully loaded.
- It’s required typecasting for getting data and check for null values to avoid error.
- It’s used to store only one time messages like error messages, validation messages.

Session
- In ASP.NET MVC, Session is a property of Controller class whose type is HttpSessionStateBase.
public HttpSessionStateBase Session { get; }
- Session is also used to pass data within the ASP.NET MVC application and Unlike TempData, it persist data for a user session until it is time out (by default session timeout is 20 minutes).
- Session is valid for all requests, not for a single redirect.
- It’s also required typecasting for getting data and check for null values to avoid error.

What are the different ways to handle exception in MVC?

1) Web.Config customErrors
2) MVC HandleErrorAttribute
3) Controller.OnException method
4) HttpApplication Application_Error event.

Controller

What is Controller in MVC?

Controllers are the components which handle user interaction, work with the Model and select a View to render.

How can we pass the data From Controller To View In MVC?

- ViewData, ViewBag, TempData.

How you return partial view from controller?

To return a Partial view from the controller action method, we can write return type as PartialViewResult and return using PartialView method.

public PartialViewResult GetCustomers()
{
return PartialView("_GetCustomer"); // returns view with model
}

Your are developing asp.net mvc application in which you want to allow access of certain method in your controller class to a role named client how you achieve this goal?

Your newly developed web application in ASP.Net MVC have found major bug on Customer controller. Right now you just want to skip all Customer pages until the bug is fixed. How could you achieve this task?

- Add route.IgnoreRoute(“Customer/”); to the RegisterRoute method.

How to know whether a request is a child request in normal action method of controller?

By using ControllerContext.IsChildAction property

In MVC, how you redirect from controller one to another controller?

Use the RedirectToAction overloads that take the controller name too...
return RedirectToAction("Index", "Controller2");

Action

What is Action method in ASP.NET MVC?

Any public method on a Controller consider as an Action.

How can we detect that a action is called by POST or GET?

using Request.HttpMethod method.

List out different return types of a controller action method?

The ASP.NET MVC framework supports several types of action results including:
ViewResult - Represents HTML and markup.
EmptyResult - Represents no result.
RedirectResult - Represents a redirection to a new URL.
JsonResult - Represents a JavaScript Object Notation result that can be used in an AJAX application.
JavaScriptResult - Represents a JavaScript script.
ContentResult - Represents a text result.
FileContentResult - Represents a downloadable file (with the binary content).
FilePathResult - Represents a downloadable file (with a path).
FileStreamResult - Represents a downloadable file (with a file stream).

Can you restrict Action method to be called only GET, POST, PUT, DELETE?

Yes, using Http verbs on Action method.
[HttpGet] // other way [AcceptVerbs(HttpVerbs.Get)]
public ActionResult Index()
{
//TODO:
return View();
}

What are child actions in ASP.Net MVC?

Child action is a controller action that you could invoke from the view

How to define controlller action is a child action ?

Using ChildActionOnly attribute.

How we can invoke child actions in ASP.Net MVC?

using the Html.Action helper:
@Html.Action("SomeActionName", "SomeController")

How can you handle multiple Submit buttons pointing to multiple actions in a single MVC view?

There are many ways, some of them are listed below.
- Multiple buttons with the same name
@using (Html.BeginForm("ProcessForm", "Home", FormMethod.Post))
{
    @Html.EditorForModel()
    <br />
    <input type="submit" name="submit" value="Save" />
    <input type="submit" name="submit" value="Cancel" />
}
[HttpPost]
public ActionResult ProcessForm(Customer obj, string submit)
{
    switch(submit)
    {
        case "Save":
            ViewBag.Message = "Customer saved successfully!";
            break;
        case "Cancel":
            ViewBag.Message = "The operation was cancelled!";
            break;
    }
    return View("Result", obj);
}
- Using HTML5 formaction and formmethod attributes
@using (Html.BeginForm())
{
    @Html.EditorForModel()
    <br />
    <input type="submit" name="save" value="Save"
              formaction="SaveForm" formmethod="post" />
    <input type="submit" name="cancel" value="Cancel"
              formaction="CancelForm" formmethod="post" />
}
[HttpPost]
public ActionResult SaveForm(Customer obj)
{
    ViewBag.Message = "Customer saved successfully!";
    return View("Result", obj);
}
[HttpPost]
public ActionResult CancelForm(Customer obj)
{
    ViewBag.Message = "The operation was cancelled!";
    return View("Result", obj);
}
- Using jQuery / JavaScript code
@using (Html.BeginForm())
{
    @Html.EditorForModel()
    <br />
    <input type="submit" id="save" value="Save" />
    <input type="submit" id="cancel" value="Cancel" />
}
$(document).ready(function () {
    $("#save").click(function () {
        $("form").attr("action", "/home/saveform");
    });
    $("#cancel").click(function () {
        $("form").attr("action", "/home/cancelform");
    });
});

What is the default Action Method when an MVC project gets created?

Index action method of Home controller.

How to prevent a browser from calling an action method of MVC?

- By using ChildActionOnly attribute.

What is CSRF attack and how can we prevent the same in MVC?

First apply “ValidateAntiForgeryToken” attribute on the action.
Second in the HTML UI screen call “@Html.AntiForgeryToken()” to generate the token.

How can you override the action name?

Can you change action name?

- using ActionName attribute.

How can you override the action method?

Overriding not possible but there is way to change action name using ActionName attribute.

Can we change action name in Web API?

Yes, using ActionName attribute.

Can you restrict WEB API Action method to be called only GET, POST, PUT, DELETE?

Yes, using Http verbs on Action method.
[HttpGet] // other way [AcceptVerbs(HttpVerbs.Get)]

How you prevent public method in controller class to act as Action method?

- using NonAction attribute

Action Result

What is Action Result in ASP.NET MVC?

A controller action returns something called an action result. An action result is what a controller action returns in response to a browser request.

What are the different types of Action Results?

The ASP.NET MVC framework supports several types of action results including:

ViewResult - Represents HTML and markup.
EmptyResult - Represents no result.
RedirectResult - Represents a redirection to a new URL.
JsonResult - Represents a JavaScript Object Notation result that can be used in an AJAX application.
JavaScriptResult - Represents a JavaScript script.
ContentResult - Represents a text result.
FileContentResult - Represents a downloadable file (with the binary content).
FilePathResult - Represents a downloadable file (with a path).
FileStreamResult - Represents a downloadable file (with a file stream).

Which is the base class for all the result type which returns from Action?

ActionResult class is a base class for all result type.

Which Action Result you will return from an Action method, if you don't want to return anything from action?

EmptyResult

What if return type of action method is string then what type of action result it is?

It will auto convert in ContentResult

Filters

What is Filter is Asp.Net MVC?

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

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

1. Global
2. Controller
3. Action

What are the different types of filters in asp.net mvc application? OR
Mention some action filter which are used regularly in ASP.Net MVC?

The ASP.NET MVC framework provides five types of filters.
    Authentication filters (introduced in MVC5)
    Authorization filters
    Action filters
    Result filters
    Exception filters

How to configure filters in ASP.NET MVC?

In Application_Start event you can register filter in GlobalFilterCollection.
eg: protected void Application_Start()
        {
            GlobalFilters.Filters.Add(new HandleErrorAttribute());
        }

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

1. Authentication filters
2. Authorization filters
3. Action filters
4. Result filters
5. Exception filters

Is it possible to override the default order, if yes how?

Yes, by using Order property of filter attribute.

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

Authentication filter

What filters are executed in the end?

Exception Filters

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

1. RequireHttpsAttribute
2. AuthorizeAttribute

What if Action filter applied on global level, controller and on action method, in which order they execute?

The order in which filter methods are called for synchronous Action filters.
Sequence    Filter scope    Filter method
1    Global    OnActionExecuting
2    Controller    OnActionExecuting
3    Method    OnActionExecuting
4    Method    OnActionExecuted
5    Controller    OnActionExecuted
6    Global    OnActionExecuted

Is it possible to create a custom action filter?

Yes, by implementing IActionFilter interface.

Is it possible to cancel filter execution?

Yes

What type of filter does OutputCacheAttribute class represents?

Result Filter

How you prevent CSRF (Cross-Site Request Forgery) in Asp.Net MVC?
In Asp.Net MVC, which Action Filter helps to prevent cross site request forgeries?

using ValidateAntiForgeryToken attribute.

How you prevent XSS (Cross Site Scripting) attacks in Asp.Net MVC?
In Asp.Net Mvc, which Action Filter used to turn off the request validation ?

using ValidateInput attribute.
You can turn it off using ValidateInput(false);

Area

What is Area in MVC?

Using Area in MVC you can split large application structure into small groups.
Each Area itself contains a MVC folder structure and in routing you need to add additional parameter 'area'.
e.g: http://localhost/AreaExample/Home/Index
AreaExampleAreaRegistration.cs
public override void RegisterArea(AreaRegistrationContext context)
        {
            context.MapRoute(
                name: "AreaExample_default",
                url: "AreaExample/{controller}/{action}/{id}",
                defaults: new {controller="Home", action = "Index", id = UrlParameter.Optional }
            );
        }

What if more the one Area have same controller name ?
How you can define default area in routing for application?

In RouteConfig.cs you need to add additional parameter 'namespaces' in MapRoute.
eg:
RouteConfig.cs
public static void RegisterRoutes(RouteCollection routes)
        {
            routes.MapRoute(
                name: "Default",
                url: "{controller}/{action}/{id}",
                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional },
                namespaces: new [] { "LearnOnlineAspNet.MVCexample.Areas.AreaExample.Controllers" }
            );
        }

How to register Area in MVC?

In Application_Start event of Global.asax.cs file call the AreaRegistration.RegisterAllAreas() method.
eg: public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
        }
    }

MODEL or Model Binding

What is Model in Asp.Net MVC?
How Model in MVC different from ViewState in WebForms?

- Model focusses only on the data, whereas View state holds the control related properties like color, font etc

How to use more than one Models in Single View?

- You can create an another model which is the combination of those models and in return that Model.
- @model Tuple<ModelA, ModelB>*

What if Action returning different models on different conditions then what will you define Model in view?

@model IEnumerable<dynamic>

How to check model is valid or not on Action method.

using Model.IsValid property.

What are Model Binders in ASP.Net MVC?

Model binding maps data from HTTP requests to action method parameters.

What are different ways you can bind model with action?
What is the order of Model Binders?

There are 3 ways to send the data using HTTP request and model binding order
- Form values
- Route values
- Query strings

Can you override the default model binder in Asp.Net MVC?

Yes, you can override the default data source, and specify the model binder's data source.
Below is a list of model binding attributes:
[BindRequired]: This attribute adds a model state error if binding cannot occur.
[BindNever]: Tells the model binder to never bind to this parameter.
[FromHeader], [FromQuery], [FromRoute], [FromForm]: Use these to specify the exact binding source you want to apply.
[FromServices]: This attribute uses dependency injection to bind parameters from services.
[FromBody]: Use the configured formatters to bind data from the request body. The formatter is selected based on content type of the request.
[ModelBinder]: Used to override the default model binder, binding source and name.

Can you create your own custom model binder?

Yes, by implement IModelBinder or IModelBinderProvider.

VIEW

What is View in Asp.Net MVC?

View is responsible for present content through the user interface. We use the 'Razor View Engine' to embed .Net code in HTML markup.

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 a View Engine?

View Engines are responsible for generating the HTML from the views.

What are the asp.net mvc view engines?

1. Razor
2. .aspx

Can you create your own view engine in Asp.Net MVC?

Yes

What is ViewModel in MVC?

ViewModel is a plain class with properties, which is used to bind it to strongly typed view. ViewModel can have the validation rules defined for its properties using data annotations.

What is PartialView in Asp.Net MVC?

A partial view is a view that is rendered within another view.

When Should I Use Partial Views?

Reusable content can be encapsulated into partial views.

What are the different ways to render Partial View?

1. Static Partial View: Static Partial View is used to render the static data.
@{Html.RenderPartial(“_PartialView”);} - It will return the void. Displays the output on your view page.
@Html.Partial(“_PartialView”); - It will return MVC HTML string, you can store it in a particular variable.
2. Dynamic Partial View: Dynamic Partial Views are used to implement the dynamic data.
@{Html.RenderAction(“_PartialView”);} - It will return MVC HTML string.
@Html.Action(“_PartialView”);

Is it possible to AJAX - update a partial view?

Yes, if you have routing set up targeting the partial view.

Can the partial view submit to a different controller than in the containing view?

Yes if you have a separate form in the partial view.

What are the differences between Partial View and Display Template and Edit Templates in ASP.Net MVC?

Display Templates : These are model centric. Meaning it depends on the properties of the view model used. It uses convention that will only display like divs or labels.
Edit Templates : These are also model centric but will have editable controls like Textboxes.
Partial View : These are view centric. These will differ from templates by the way they render the properties (Id's) Eg : CategoryViewModel has Product class property then it will be rendered as Model.Product.ProductName but in case of templates if we CategoryViewModel has List then @Html.DisplayFor(m => m.Products) works and it renders the template for each item of this list.

What is Layout in View?

Layout is a View which contain all the common html markup of the site template and by inheriting it we can create other views, which help to not rewrite the same markup of each html or view file and also help for consistent look and feel throughout the site.

What are the different ways to render layout in Asp.Net MVC?

1. Using _Viewstart file in shared folder.
2. Adding _ViewStart file in each of the directories.
3. Defining Layout with in each view on the top
{Layout = "~/Views/Shared/_AdminLayout.cshtml";}
4.Returning Layout from ActionResult
public
ActionResultIndex(){
RegisterModelmodel = newRegisterModel();
//TO DO:
returnView("Index", "_AdminLayout", model);
}

What is RenderBody in Layout View?

How many RenderBody you can define in Layout View?

Only one and it is also mandatory to define for Layout view.

What is Section in Layout View?

Sections provide a way to organize where certain page elements should be placed.

How to make it mandatory for child view to implement Section?

By using required parameter true
eg:
@RenderSection("scripts", required: true)

How to check whether the Section exist on View or not?

- By using IsSectionDefined("sectionName") method.

How many Section you can define in view?

More than one.

What is the difference between PartialView and Section ?

PartialView is module you can share among views. Section is specific to view.

Can you return view by using WEBAPI method?

No.

Is there a need for you to perform any special steps in Razor views, to protect the ASP.NET MVC application from cross-site scripting (XSS) attacks?

No; by default, content emitted using a @ block is automatically HTML encoded to protect the ASP.NET MVC application from XSS attacks.

What is Strongly-Typed View?

Strongly type view is used for rendering specific type of model object in View. View inherits from Viewpage whereas strongly typed view inherits from Viewpage where T is type of the model.

Routing

What is routing in MVC?

- Routing is a pattern matching system which matching the incoming request URL pattern with the patterns defined in Route table.

How router is working in MVC?

- Requests to an ASP.NET MVC-based Web application first pass through the UrlRoutingModule object, which is an HTTP module. The UrlRoutingModule searches the routes defined in the routes table and selects the first route object that matches the current request.

How to define route in MVC?
Where is the route mapping code written?
What is Default Route in MVC?
How route table created in MVC?

Route must be registered in Application_Start event in Global.ascx.cs file.

public class MvcApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
RegisterRoutes(RouteTable.Routes);
}
public static void RegisterRoutes(RouteCollection routes)
{
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Home", action = "Index", id = "" } // Parameter defaults
);
}
}

What are the segments of routing important?
What are the minimum segments required to create a route in ASP.Net MVC?

- Route Name and Url

What are the different ways you can define route in Asp.Net MVC?

- Convention-based routing AND Attribute routing introduced in MVC 5

What is difference between routing and url rewriting?

Routing in MVC match the url pattern with RouteTable and process.
Url Rewriting mapped url to another url.

In MVC is mandatory to be Map route {controller}/{action}/{id} In This format only..??

- No.

What is Route Constraints in MVC?
How do you add constraints to a route ?
What are the two ways for adding constraints to a route?

Using regular expressions
Using an object that implements IRouteConstraint interface

How can we define the route prefix for all actions in the controller?

Using Route attribute on Controller

What is RouteConfig.cs in MVC?

- RouteConfig class containing the static RegisterRoutes method where we adding route in route table.

Can we map multiple URLs to the same action?

Yes but it invoked only one which match first in route table.

Explain attribute based routing in MVC?

Attribute routing introduced in MVC 5 and it enables you to specify routing information by decorating your controllers and actions with attributes 'Route' that define your application’s routes.

public class ProductsController : Controller
{
[Route("product/{id}")]
public IActionResult GetProduct(int id)
{
...
}
}

How to enable Attribute Routing?

- when you registering route in application_start event, call the method 'MapMvcAttributeRoutes()' of route collection .

How to define Attribute routing for Area in MVC?

How route table has been created in ASP.Net MVC?

Explain the difference between adding routes to a web application and MVC application?

Why to use "{resource}.axd/{*pathInfo}" in routing in ASP.Net MVC?

Mention two instances where routing is not implemented or required?

Explain with examples for scenarios when routing is not applied ?

What is the difference between Url.RouteUrl and Url.HttpRouteUrl?

What is 'catch-all' route in Asp.Net MVC?
Is there any way to handle variable number of segments in a route definition?

When someone would request a resource that fails a constraint the catch-all route would match the request.
routes.MapRoute(
"NotFound",
"{*url}",
new { controller = "Error", action = "PageNotFound" }
);

How to enable Attribute routing in Web API?

- when you registering route in application_start event, call the method 'MapHttpAttributeRoutes()' of HttpConfiguration .

How to define Attribute routing in Web API?

- Route must be registered in Application_Start event in Global.ascx.cs file.
public static void Register(HttpConfiguration config)
{
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
}
}

SCENARIO
You have already develop ASP.Net MVC Web application. you have to work in already developed an HTTP module. can you redirect the request to a different handler that is in the routing table? if you can do this, what event would you handle ?

- handle the MapRequestHandler event

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Interview Questions - Asp.Net MVC