What are the different types of results in MVC?

Note: It’s difficult to remember all the 12 types. But some important ones you can remember for the interview are ActionResult, ViewResult, and JsonResult. Below is a detailed list for your interest:

There 12 kinds of results in MVC, at the top is the ActionResult class which is a base class that can have 11 subtypes as listed below:

1. ViewResult - Renders a specified view to the response stream
2. PartialViewResult - Renders a specified partial view to the response stream
3. EmptyResult - An empty response is returned
4. RedirectResult - Performs an HTTP redirection to a specified URL
5. RedirectToRouteResult - Performs an HTTP redirection to a URL that is determined by the routing engine, based on given route data
6. JsonResult - Serializes a given ViewData object to JSON format
7. JavaScriptResult - Returns a piece of JavaScript code that can be executed on the client
8. ContentResult - Writes content to the response stream without requiring a view
9. FileContentResult - Returns a file to the client
10. FileStreamResult - Returns a file to the client, which is provided by a Stream
11. FilePathResult - Returns a file to the client

What is the difference between ActionResult and ViewResult?

• ActionResult is an abstract class while ViewResult derives from the  ActionResult class.  ActionResult has several derived classes like  ViewResult, JsonResult,  FileStreamResult  and  so on.

• ActionResult can be used to exploit polymorphism and dynamism. So if you are returning different types of views dynamically, ActionResult is the best thing. For example in the below code snippet, you can see we have a simple action called DynamicView. Depending on the flag (IsHtmlView) it will either return a ViewResult or JsonResult.

public ActionResult DynamicView()
{
   if (IsHtmlView)
     return View(); // returns simple ViewResult
   else
     return Json(); // returns JsonResult view
} 

How to implement AJAX in MVC?

You can implement AJAX in two ways in MVC:

• AJAX libraries
• jQuery

Below is a simple sample of how to implement AJAX by using the “AJAX” helper library. In the below code you can see we have a simple form which is created by using the Ajax.BeginForm syntax. This form calls a controller action called getCustomer. So now the submit action click will be an asynchronous AJAX call.

<script language="javascript">
function OnSuccess(data1) 
{
// Do something here
}
</script>
<div>
<%
        var AjaxOpt = new AjaxOptions{OnSuccess="OnSuccess"};        
    %>
<% using (Ajax.BeginForm("getCustomer","MyAjax",AjaxOpt)) { %>
<input id="txtCustomerCode" type="text" /><br />
<input id="txtCustomerName" type="text" /><br />
<input id="Submit2" type="submit" value="submit"/></div>
<%} %> 

In case you want to make AJAX calls on hyperlink clicks, you can use the Ajax.ActionLink function as shown in the below code.

Figure: Implement AJAX in MVC

So if you want to create an AJAX asynchronous hyperlink by name GetDate which calls the GetDate function in the controller, below is the code for that. Once the controller responds, this data is displayed in the HTML DIV tag namedDateDiv.

<span id="DateDiv" />
<%: 
Ajax.ActionLink("Get Date","GetDate",
new AjaxOptions {UpdateTargetId = "DateDiv" })
%> 

Below is the controller code. You can see how the GetDate function has a pause of 10 seconds.

public class Default1Controller : Controller
{
   public string GetDate()
   {
       Thread.Sleep(10000);
       return DateTime.Now.ToString();
   }
}

The second way of making an AJAX call in MVC is by using jQuery. In the below code you can see we are making an AJAX POST call to a URL /MyAjax/getCustomer. This is done by using $.post. All this logic is put into a function calledGetData and you can make a call to the GetData function on a button or a hyperlink click event as you want.

function GetData() 
{
    var url = "/MyAjax/getCustomer";
    $.post(url, function (data) 
    {
        $("#txtCustomerCode").val(data.CustomerCode);
        $("#txtCustomerName").val(data.CustomerName);
    }
    )
} 

What kind of events can be tracked in AJAX?

Figure: Tracked in AJAX

How can you do authentication and authorization in MVC?

You can use Windows or Forms authentication for MVC.

How to implement Windows authentication for MVC?

For Windows authentication you need to modify the web.config file and set the authentication mode to Windows.

<authentication mode="Windows"/>
<authorization>
<deny users="?"/>
</authorization> 

Then in the controller or on the action, you can use the Authorize attribute which specifies which users have access to these controllers and actions. Below is the code snippet for that. Now only the users specified in the controller and action can access it.

[Authorize(Users= @"WIN-3LI600MWLQN\Administrator")]
public class StartController : Controller
{
    //
    // GET: /Start/
    [Authorize(Users = @"WIN-3LI600MWLQN\Administrator")]
    public ActionResult Index()
    {
        return View("MyView");
    }
} 

How do you implement Forms authentication in MVC?

Forms authentication is implemented the same way as in ASP.NET. The first step is to set the authentication mode equal to Forms. The loginUrl points to a controller here rather than a page.

<authentication mode="Forms">
<forms loginUrl="~/Home/Login"  timeout="2880"/>
</authentication> 

We also need to create a controller where we will check if the user is proper or not. If the user is proper we will set the cookie value.

public ActionResult Login()
{
    if ((Request.Form["txtUserName"] == "Shiv") && 
          (Request.Form["txtPassword"] == "Shiv@123"))
    {
        FormsAuthentication.SetAuthCookie("Shiv",true);
        return View("About");
    }
    else
    {
        return View("Index");
    }
} 

All the other actions need to be attributed with the Authorize attribute so that any unauthorized user making a call to these controllers will be redirected to the controller (in this case the controller is “Login”) which will do the authentication.

[Authorize]
PublicActionResult Default()
{
return View();
}
[Authorize]
publicActionResult About()
{
return View();
} 

How can we use two ( multiple) models with a single view?

When we bind a model with a view we use the model dropdown as shown in the below figure. In the below figure we can only select one model.

But what if we want to bind “Customer” as well as “Order” class to the view.

For that we need to create a view model which aggregates both the classes as shown in the below code. And then bind that view model with the view.

public class CustOrderVM
{


public  Customer cust = new Customer();

public Order Ord = new Order();

}

In the view we can refer both the model using the view model as shown in the below code.

<%= model.cust.Name %>

<%= model.Ord.Number %>

Explain the need of display mode in MVC?

Display mode displays views depending on the device the user has logged in with. So we can create different views for different devices anddisplay mode will handle the rest.

For example we can create a view “Home.aspx” which will render for the desktop computers and Home.Mobile.aspx for mobile devices. Now when an end user sends a request to the MVC application, display mode checks the “user agent” headers and renders the appropriate view to the device accordingly.

Explain MVC model binders?

Model binder maps HTML form elements to the model. It acts like a bridge between HTML UI and MVC model. Many times HTML UI names are different than the model property names. So in the binder we can write the mapping logic between the UI and the model.

What is Razor in MVC?

It’s a light weight view engine. Till MVC we had only one view type, i.e., ASPX. Razor was introduced in MVC 3.

Why Razor when we already have ASPX?

Razor is clean, lightweight, and syntaxes are easy as compared to ASPX. For example, in ASPX to display simple time, we need to write:

<%=DateTime.Now%> 

In Razor, it’s just one line of code:

@DateTime.Now

So which is a better fit, Razor or ASPX?

As per Microsoft, Razor is more preferred because it’s light weight and has simple syntax.

Where is the route mapping code written?

The route mapping code is written in the “global.asax” file.

Can we map multiple URL’s to the same action?

Yes, you can, you just need to make two entries with different key names and specify the same controller and action.

How can we navigate from one view to another using a hyperlink?

By using the ActionLink method as shown in the below code. The below code will create a simple URL which helps to navigate to the “Home” controller and invoke the GotoHome action.

<%= Html.ActionLink("Home","Gotohome") %>  

How can we restrict MVC actions to be invoked only by GET or POST?

We can decorate the MVC action with the HttpGet or HttpPost attribute to restrict the type of HTTP calls. For instance you can see in the below code snippet the DisplayCustomer action can only be invoked by HttpGet. If we try to make HTTP POST on DisplayCustomer, it will throw an error.

[HttpGet]
public ViewResult DisplayCustomer(int id)
{
    Customer objCustomer = Customers[id];
    return View("DisplayCustomer",objCustomer);
} 

How can we maintain sessions in MVC?

Sessions can be maintained in MVC by three ways: tempdata, viewdata, and viewbag.

What is routing in MVC?

Routing helps you to define a URL structure and map the URL with the controller.

For instance let’s say we want that when a user types “http://localhost/View/ViewCustomer/”, it goes to the “Customer” Controller and invokes the DisplayCustomer action. This is defined by adding an entry in to the routes collection using the MapRoute function. Below is the underlined code which shows how the URL structure and mapping with controller and action is defined.

routes.MapRoute(

               "View", // Route name

               "View/ViewCustomer/{id}", // URL with parameters

               new { controller = "Customer", action = "DisplayCustomer", 

               id = UrlParameter.Optional }); // Parameter defaults   

What is the difference between “HTML.TextBox” vs “HTML.TextBoxFor”?

Both of them provide the same HTML output, “HTML.TextBoxFor” is strongly typed while “HTML.TextBox” isn’t. Below is a simple HTML code which just creates a simple textbox with “CustomerCode” as name.

Html.TextBox("CustomerCode")

Below is “Html.TextBoxFor” code which creates HTML textbox using the property name ‘CustomerCode” from object “m”.

Html.TextBoxFor(m => m.CustomerCode)

In the same way we have for other HTML controls like for checkbox we have “Html.CheckBox” and “Html.CheckBoxFor”.

What are HTML helpers in MVC?

HTML helpers help you to render HTML controls in the view. For instance if you want to display a HTML textbox on the view , below is the HTML helper code.

<%= Html.TextBox("LastName") %>

For checkbox below is the HTML helper code. In this way we have HTML helper methods for every HTML control that exists.

<%= Html.CheckBox("Married") %>

What is the difference between each version of MVC?

Below is a detailed table of differences. But during an interview it’s difficult to talk about all of them due to time limitation. So I have highlighted the important differences that you can run through before the interviewer.

MVC 2	MVC 3	MVC 4
Client-side validation Templated Helpers Areas Asynchronous Controllers Html.ValidationSummary Helper Method DefaultValueAttribute in Action-Method Parameters binding Binary data with Model Binders DataAnnotations Attributes Model-Validator Providers New RequireHttpsAttributeAction Filter Templated Helpers Display Model-Level Errors	Razor Readymade project templates HTML 5 enabled templates Support for Multiple View Engines, JavaScript, and AJAX Model Validation Improvements	ASP.NET Web API Refreshed and modernized default project templates. New mobile project template. Many new features to support mobile apps Enhanced support for asynchronous methods

Is MVC different from a three layered architecture?

MVC is an evolution of a three layered traditional architecture. Many components of the three layered architecture are part of MVC. So below is how the mapping goes:

Functionality	Three layered / tiered architecture	Model view controller architecture
Look and Feel	User interface	View
UI logic	User interface	Controller
Business logic /validations	Middle layer	Model
Request is first sent to	User interface	Controller
Accessing data	Data access layer	Data Access Layer

Figure: Three layered architecture

What are the benefits of using MVC?

There are two big benefits of MVC:

• Separation of concerns is achieved as we are moving the code-behind to a separate class file. By moving the binding code to a separate class file we can reuse the code to a great extent.

• Automated UI testing is possible because now the behind code (UI interaction code) has moved to a simple .NET class. This gives us opportunity to write unit tests and automate manual testing.

Is MVC suitable for both Windows and Web applications ?

The MVC architecture is suited for a web application than Windows. For Window applications, MVP, i.e., “Model View Presenter” is more applicable. If you are using WPF and Silverlight, MVVM is more suitable due to bindings.

Explain MVC application life cycle ?

There are six broader events which occur in MVC application life cycle below diagrams summarize it.

Image Courtesy: - http://www.dotnetinterviewquestions.in/article_explain-mvc-application-life-cycle_210.html

Any web application has two main execution steps first understanding the request and depending on the type of the request sending out appropriate response. MVC application life cycle is not different it has two main phases first creating the request object and second sending our response to the browser.

Creating the request object: -The request object creation has four major steps. Below is the detail explanation of the same.

Step 1 Fill route: - MVC requests are mapped to route tables which in turn specify which controller and action to be invoked. So if the request is the first request the first thing is to fill the route table with routes collection. This filling of route table happens in the global.asax file.

Step 2 Fetch route: - Depending on the URL sent “UrlRoutingModule” searches the route table to create “RouteData” object which has the details of which controller and action to invoke.

Step 3 Request context created: - The “RouteData” object is used to create the “RequestContext” object.

Step 4 Controller instance created: - This request object is sent to “MvcHandler” instance to create the controller class instance. Once the controller class object is created it calls the “Execute” method of the controller class.

Creating Response object: - This phase has two steps executing the action and finally sending the response as a result to the view.

What is MVC (Model View Controller) ?

MVC is an architectural pattern which separates the representation and user interaction. It’s divided into three broader sections, Model, View, and Controller. Below is how each one of them handles the task.

• The View is responsible for the look and feel.
• Model represents the real world object and provides data to the View.
• The Controller is responsible for taking the end user request and loading the appropriate Model and View.

Figure: MVC (Model view controller)

Can we display all errors in one go?

Yes, we can; use the ValidationSummary method from the Html helper class.

<%= Html.ValidationSummary() %>   

What are the other data annotation attributes for validation in MVC?

If you want to check string length, you can use StringLength.

[StringLength(160)]
public string FirstName { get; set; }

In case you want to use a regular expression, you can use the RegularExpression attribute.

[RegularExpression(@"[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}")]

public string Email { get; set; }

If you want to check whether the numbers are in range, you can use the Range attribute.

 

[Range(10,25)]

public int Age { get; set; }

Sometimes you would like to compare the value of one field with another field, we can use the Compare attribute.

public string Password { get; set; }

[Compare("Password")]

public string ConfirmPass { get; set; }

In case you want to get a particular error message , you can use the Errors collection.

var ErrMessage = ModelState["Email"].Errors[0].ErrorMessage;

If you have created the model object yourself you can explicitly call TryUpdateModel in your controller to check if the object is valid or not.

TryUpdateModel(NewCustomer);

In case you want add errors in the controller you can use the AddModelError function.

ModelState.AddModelError("FirstName", "This is my server-side error.");