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)
There are six broader events which occur in MVC application life cycle below diagrams summarize it.
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.
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.
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.
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
When this note was written, four versions were released of MVC: MVC 1 , MVC 2, MVC 3, and MVC 4. So the latest is MVC 4.
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 |
|
|
|
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") %>
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”.
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
The route mapping code is written in the “global.asax” file.
Yes, you can, you just need to make two entries with different key names and specify the same controller and action.
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") %>
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);
}
Sessions can be maintained in MVC by three ways: tempdata, viewdata, and viewbag.
Figure: Difference between tempdata, viewdata, and viewbag
- Temp data - Helps to maintain data when you move from one controller to another controller or from one action to another action. In other words when you redirect, tempdata helps to maintain data between those redirects. It internally uses session variables.
- View data - Helps to maintain data when you move from controller to view.
- View Bag - It’s a dynamic wrapper around view data. When you use Viewbag type, casting is not required. It uses the dynamic keyword internally.
Figure: dynamic keyword
- Session variables - By using session variables we can maintain data from any entity to any entity.
- Hidden fields and HTML controls - Helps to maintain data from UI to controller only. So you can send data from HTML controls or hidden fields to the controller using POST or GET HTTP methods.
Below is a summary table which shows the different mechanisms for persistence.
Maintains data between
|
ViewData/ViewBag
|
TempData
|
Hidden fields
|
Session
|
Controller to Controller
|
No
|
Yes
|
No
|
Yes
|
Controller to View
|
Yes
|
No
|
No
|
Yes
|
View to Controller
|
No
|
No
|
Yes
|
Yes
|
Partial view is a reusable view (like a user control) which can be embedded inside other view. For example let’s say all your pages of your site have a standard structure with left menu, header, and footer as shown in the image below.
Figure: Partial views in MVC
For every page you would like to reuse the left menu, header, and footer controls. So you can go and create partial views for each of these items and then you call that partial view in the main view.
When you add a view to your project you need to check the “Create partial view” check box.
Figure: Create partial view
Once the partial view is created you can then call the partial view in the main view using the Html.RenderPartial method as shown in the below code snippet:
<body>
<div>
<% Html.RenderPartial("MyView"); %>
</div>
</body>
One of the easiest ways of doing validation in MVC is by using data annotations. Data annotations are nothing but attributes which can be applied on model properties. For example, in the below code snippet we have a simple Customer class with a property customercode.
This CustomerCode property is tagged with a Required data annotation attribute. In other words if this model is not provided customer code, it will not accept it.
public class Customer
{
[Required(ErrorMessage="Customer code is required")]
public string CustomerCode
{
set;
get;
}
}
In order to display the validation error message we need to use the ValidateMessageFor method which belongs to the Html helper class.
<% using (Html.BeginForm("PostCustomer", "Home", FormMethod.Post))
{ %>
<%=Html.TextBoxFor(m => m.CustomerCode)%>
<%=Html.ValidationMessageFor(m => m.CustomerCode)%>
<input type="submit" value="Submit customer data" />
<%}%>
Later in the controller we can check if the model is proper or not by using the ModelState.IsValid property and accordingly we can take actions.
public ActionResult PostCustomer(Customer obj)
{
if (ModelState.IsValid)
{
obj.Save();
return View("Thanks");
}
else
{
return View("Customer");
}
}
Below is a simple view of how the error message is displayed on the view.
Figure: Validations in MVC
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.");
It’s a two-step process: first reference the necessary jQuery files.
<script src="<%= Url.Content("~/Scripts/jquery-1.5.1.js") %>" type="text/javascript"></script>
<script src="<%= Url.Content("~/Scripts/jquery.validate.js") %>" type="text/javascript"></script>
<script src="<%= Url.Content("~/Scripts/jquery.validate.unobtrusive.js") %>" type="text/javascript"></script>
The second step is to call the EnableClientValidation method.
<% Html.EnableClientValidation(); %>
It’s a light weight view engine. Till MVC we had only one view type, i.e., ASPX. Razor was introduced in MVC 3.
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
As per Microsoft, Razor is more preferred because it’s light weight and has simple syntaxes.
You can use Windows or Forms 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");
}
}
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();
}
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 named DateDiv.
<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 called GetData 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);
}
)
}
Figure: Tracked in AJAX
- 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
}
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
ActionFilters help you to perform logic while an MVC action is executing or after an MVC action has executed.
Figure: ActionFilters in MVC
Action filters are useful in the following scenarios:
1. Implement post-processing logic before the action happens.
2. Cancel a current execution.
3. Inspect the returned value.
4. Provide extra data to the action.
You can create action filters by two ways:
- Inline action filter.
- Creating an ActionFilter attribute.
To create an inline action attribute we need to implement the IActionFilter interface. The IActionFilter interface has two methods: OnActionExecuted and OnActionExecuting. We can implement pre-processing logic or cancellation logic in these methods.
public class Default1Controller : Controller , IActionFilter
{
public ActionResult Index(Customer obj)
{
return View(obj);
}
void IActionFilter.OnActionExecuted(ActionExecutedContext filterContext)
{
Trace.WriteLine("Action Executed");
}
void IActionFilter.OnActionExecuting(ActionExecutingContext filterContext)
{
Trace.WriteLine("Action is executing");
}
}
The problem with the inline action attribute is that it cannot be reused across controllers. So we can convert the inline action filter to an action filter attribute. To create an action filter attribute we need to inherit from ActionFilterAttribute and implement the IActionFilter interface as shown in the below code.
public class MyActionAttribute : ActionFilterAttribute , IActionFilter
{
void IActionFilter.OnActionExecuted(ActionExecutedContext filterContext)
{
Trace.WriteLine("Action Executed");
}
void IActionFilter.OnActionExecuting(ActionExecutingContext filterContext)
{
Trace.WriteLine("Action executing");
}
}
Later we can decorate the controllers on which we want the action attribute to execute. You can see in the below code I have decorated the Default1Controller with the MyActionAttribute class which was created in the previous code.
[MyActionAttribute]
public class Default1Controller : Controller
{
public ActionResult Index(Customer obj)
{
return View(obj);
}
}
Yes, we can create our own custom view engine in MVC. To create our own custom view engine we need to follow three steps:
Let’ say we want to create a custom view engine where in the user can type a command like “<DateTime>” and it should display the current date and time.
Step 1: We need to create a class which implements the IView interface. In this class we should write the logic of how the view will be rendered in the render function. Below is a simple code snippet for that.
public class MyCustomView : IView
{
private string _FolderPath; // Define where our views are stored
public string FolderPath
{
get { return _FolderPath; }
set { _FolderPath = value; }
}
public void Render(ViewContext viewContext, System.IO.TextWriter writer)
{
// Parsing logic <dateTime>
// read the view file
string strFileData = File.ReadAllText(_FolderPath);
// we need to and replace <datetime> datetime.now value
string strFinal = strFileData.Replace("<DateTime>", DateTime.Now.ToString());
// this replaced data has to sent for display
writer.Write(strFinal);
}
}
Step 2: We need to create a class which inherits from VirtualPathProviderViewEngine and in this class we need to provide the folder path and the extension of the view name. For instance, for Razor the extension is “cshtml”; for aspx, the view extension is “.aspx”, so in the same way for our custom view, we need to provide an extension. Below is how the code looks like. You can see the ViewLocationFormats is set to the Views folder and the extension is “.myview”.
public class MyViewEngineProvider : VirtualPathProviderViewEngine
{
// We will create the object of Mycustome view
public MyViewEngineProvider() // constructor
{
// Define the location of the View file
this.ViewLocationFormats = new string[] { "~/Views/{1}/{0}.myview",
"~/Views/Shared/{0}.myview" }; //location and extension of our views
}
protected override IView CreateView(
ControllerContext controllerContext, string viewPath, string masterPath)
{
var physicalpath = controllerContext.HttpContext.Server.MapPath(viewPath);
MyCustomView obj = new MyCustomView(); // Custom view engine class
obj.FolderPath = physicalpath; // set the path where the views will be stored
return obj; // returned this view paresing
// logic so that it can be registered in the view engine collection
}
protected override IView CreatePartialView(ControllerContext controllerContext, string partialPath)
{
var physicalpath = controllerContext.HttpContext.Server.MapPath(partialPath);
MyCustomView obj = new MyCustomView(); // Custom view engine class
obj.FolderPath = physicalpath; // set the path where the views will be stored
return obj;
// returned this view paresing logic
// so that it can be registered in the view engine collection
}
}
Step 3: We need to register the view in the custom view collection. The best place to register the custom view engine in the ViewEngines collection is the global.asax file. Below is the code snippet for that.
protected void Application_Start()
{
// Step3 :- register this object in the view engine collection
ViewEngines.Engines.Add(new MyViewEngineProvider());
…..
}
Below is a simple output of the custom view written using the commands defined at the top.
Figure: Custom view engine using MVC
If you invoke this view, you should see the following output:
In MVC, we have the JsonResult class by which we can return back data in JSON format. Below is a simple sample code which returns back a Customer object in JSON format using JsonResult.
public JsonResult getCustomer()
{
Customer obj = new Customer();
obj.CustomerCode = "1001";
obj.CustomerName = "Shiv";
return Json(obj,JsonRequestBehavior.AllowGet);
}
Below is the JSON output of the above code if you invoke the action via the browser.
HTTP is the most used protocol. For the past many years, browser was the most preferred client by which we consumed data exposed over HTTP. But as years passed by, client variety started spreading out. We had demand to consume data on HTTP from clients like mobile, JavaScript, Windows applications, etc.
For satisfying the broad range of clients REST was the proposed approach. You can read more about REST from the WCF chapter.
WebAPI is the technology by which you can expose data over HTTP following REST principles.
| SOAP |
WEB API
| |
Size
|
Heavy weight because of complicated WSDL structure.
|
Light weight, only the necessary information is transferred.
|
Protocol
|
Independent of protocols.
|
Only for HTTP protocol
|
Formats
|
To parse SOAP message, the client needs to understand WSDL format. Writing custom code for parsing WSDL is a heavy duty task. If your client is smart enough to create proxy objects like how we have in .NET (add reference) then SOAP is easier to consume and call.
|
Output of WebAPI are simple string messages, JSON, simple XML format, etc. So writing parsing logic for that is very easy.
|
Principles
|
SOAP follows WS-* specification.
|
WebAPI follows REST principles. (Please refer to REST in WCF chapter.)
|
WCF was brought into implement SOA, the intention was never to implement REST. WebAPI is built from scratch and the only goal is to create HTTP services using REST. Due to the one point focus for creating REST service, WebAPI is more preferred.
How to implement WebAPI in MVC
Below are the steps to implement WebAPI:
Step 1: Create the project using the WebAPI template.
Figure: Implement WebAPI in MVC
Step 2: Once you have created the project you will notice that the controller now inherits from ApiController and you can now implement POST, GET, PUT, and DELETE methods of the HTTP protocol.
public class ValuesController : ApiController
{
// GET api/values
public IEnumerable<string> Get()
{
return new string[] { "value1", "value2" };
}
// GET api/values/5
public string Get(int id)
{
return "value";
}
// POST api/values
public void Post([FromBody]string value)
{
}
// PUT api/values/5
public void Put(int id, [FromBody]string value)
{
}
// DELETE api/values/5
public void Delete(int id)
{
}
}
Step 3: If you make an HTTP GET call you should get the below results:
Figure: HTTP
To detect if the call on the controller is a POST action or a GET action we can use the Request.HttpMethod property as shown in the below code snippet.
public ActionResult SomeAction()
{
if (Request.HttpMethod == "POST")
{
return View("SomePage");
}
else
{
return View("SomeOtherPage");
}
}
Bundling and minification helps us improve request load times of a page thus increasing performance.
Web projects always need CSS and script files. Bundling helps us combine multiple JavaScript and CSS files in to a single entity thus minimizing multiple requests in to a single request.
For example consider the below web request to a page . This page consumes two JavaScript files Javascript1.js and Javascript2.js. So when this is page is requested it makes three request calls:
- One for the Index page.
- Two requests for the other two JavaScript files: Javascript1.js and Javascript2.js.
The below scenario can become worse if we have a lot of JavaScript files resulting in multiple requests, thus decreasing performance. If we can somehow combine all the JS files into a single bundle and request them as a single unit that would result in increased performance (see the next figure which has a single request).
Open BundleConfig.cs from the App_Start folder.
In BundleConfig.cs, add the JS files you want bundle into a single entity in to the bundles collection. In the below code we are combining all the javascript JS files which exist in the Scripts folder as a single unit in to the bundle collection.
bundles.Add(new ScriptBundle("~/Scripts/MyScripts").Include(
"~/Scripts/*.js"));
Below is how your BundleConfig.cs file will look like:
public class BundleConfig
{
public static void RegisterBundles(BundleCollection bundles)
{
bundles.Add(new ScriptBundle("~/Scripts/MyScripts").Include(
"~/Scripts/*.js"));
BundleTable.EnableOptimizations = true;
}
}
Once you have combined your scripts into one single unit we then to include all the JS files into the view using the below code. The below code needs to be put in the ASPX or Razor view.
<%= Scripts.Render("~/Scripts/MyScripts") %>
If you now see your page requests you would see that script request is combined into one request.
If you are in a debug mode you need to set EnableOptimizations to true in the bundleconfig.cs file or else you will not see the bundling effect in the page requests.
BundleTable.EnableOptimizations = true;
Minification reduces the size of script and CSS files by removing blank spaces , comments etc. For example below is a simple javascript code with comments.
// This is test
var x = 0;
x = x + 1;
x = x * 2;
After implementing minification the JavaScript code looks like below. You can see how whitespaces and comments are removed to minimize file size, thus increasing performance.
var x=0;x=x+1;x=x*2;
When you implement bundling, minification is implemented by itself. In other words the steps to implement bundling and minification are the same.
Areas help you to group functionalities in to independent modules thus making your project more organized. For example in the below MVC project we have four controller classes and as time passes by if more controller classes are added it will be difficult to manage. In bigger projects you will end up with 100’s of controller classes making life hell for maintenance.
If we can group controller classes in to logical section like “Invoicing” and “Accounting” that would make life easier and that’s what “Area” are meant to.
You can add an area by right clicking on the MVC solution and clicking on “Area” menu as shown in the below figure.
In the below image we have two “Areas” created “Account” and “Invoicing” and in that I have put the respective controllers. You can see how the project is looking more organized as compared to the previous state.
A view model is a simple class which represents data to be displayed on the view.
For example below is a simple customermodel object with “CustomerName” and “Amount” property.
CustomerViewModel obj = new CustomerViewModel();
obj.Customer.CustomerName = "Shiv";
obj.Customer.Amount = 1000;
But when this “Customer” model object is displayed on the MVC view it looks something as shown in the below figure. It has “CustomerName” , “Amount” plus “Customer Buying Level” fields on the view / screen. “Customer buying Level” is a color indicationwhich indicates how aggressive the customer is buying.
“Customer buying level” color depends on the value of the “Amount property. If the amount is greater than 2000 then color is red , if amount is greater than 1500 then color is orange or else the color is yellow.
In other words “Customer buying level” is an extra property which is calculated on the basis of amount.
So the Customer viewmodel class has three properties
- “TxtCustomerName” textbox takes data from “CustomerName” property as it is.
- “TxtAmount” textbox takes data from “Amount” property of model as it is.
- “CustomerBuyingLevelColor” displays color value depending on the “Amount “ value.
Customer Model
|
Customer ViewModel
|
CustomerName
|
TxtCustomerName
|
Amount
|
TxtAmount
|
CustomerBuyingLevelColor
|
As the name says view model this class has the gel code or connection code which connects the view and the model.
So the view model class can have following kind of logics:-
- Color transformation logic: - For example you have a “Grade” property in model and you would like your UI to display “red” color for high level grade, “yellow” color for low level grade and “green” color of ok grade.
- Data format transformation logic :-Your model has a property “Status” with “Married” and “Unmarried” value. In the UI you would like to display it as a checkbox which is checked if “married” and unchecked if “unmarried”.
- Aggregation logic: -You have two differentCustomer and Address model classes and you have view which displays both “Customer” and “Address” data on one go.
- Structure downsizing: - You have “Customer” model with “customerCode” and “CustomerName” and you want to display just “CustomerName”. So you can create a wrapper around model and expose the necessary properties. <h2How can we use two ( multiple) models with a single view?
Let us first try to understand what the interviewer is asking. 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 %>
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.
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.
Please do read this blog which has detailed steps of how model binders can be created using “IModelBinder” interface: -
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