MVC Introduction, Overview & Architecture - Part 1

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iFour Consultancy
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Introduction to MVC

• Software design pattern for developing web
  applications
• Software architecture pattern which separates the
  representation of information from the users
  interaction with it
• Here M stands for Model, V stands for View
  and C stands for controller
• ASP.NET MVC helps to develop powerful and
  pattern-based dynamic websites that enables a
  clean separation of concerns and also gives full
  control on a mark-up
• Also it includes many features that help to
  develop a sophisticated and modern web application

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MVC vs WEB FORMS
MVC Web Forms
Easier to Manage Complexity Preservers State over HTTP
Does not use view state or server based forms Page Controller Pattern
Rich Routing Structure View state or server based forms
Support for Test-Driven Development Works well for small teams
Supports Large Teams Well Development is less complex
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Architecture of MVC

• A markup language is a set of markup tags

• A Model View Controller pattern is made up of the
  following three parts
• Model
• View
• Controller

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Architecture of MVC (Cont.)

• A markup language is a set of markup tags

• Model
• Responsible for managing the data of the
  application
• It responds to the request from the view and it
  also responds to instructions from the controller
  to update itself
• Lowest level pattern which is responsible for
  maintaining data
• Represents the application core (for instance a
  list of database records)
• Also called the domain layer

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Architecture of MVC (Cont.)

• A markup language is a set of markup tags

• View
• The View displays the data (the database records)
• A view requests information from the model, that
  it needs to generate an output representation
• Presents data in a particular format like JSP,
  ASP, PHP
• MVC is often seen in web applications, where the
  view is the HTML page

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Architecture of MVC (Cont.)

• A markup language is a set of markup tags

• Controller
• It is the part of the application that handles
  user interaction
• Typically controllers read data from a view,
  control user input, and send input data to the
  model
• It handles the input, typically user actions and
  may invoke changes on the model and view

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Routing

• A markup language is a set of markup tags

• A route is a URL pattern that is mapped to a
  handler
• The handler can be a physical file, such as an
  .aspx file in a Web Forms application. A handler
  can also be a class that processes the request,
  such as a controller in an MVC application
• At runtime, Routing engine use the Route table
  for matching the incoming request's URL pattern
  against the URL patterns defined in the Route
  table
• Register one or more URL patterns to the Route
  table at Application_Start event
• When the routing engine finds a match in the
  route table for the incoming request's URL, it
  forwards the request to the appropriate
  controller and action
• If there is no match in the route table for the
  incoming request's URL, it returns a 404 HTTP
  status code

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How it works?

• A markup language is a set of markup tags

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How to define route?

• A markup language is a set of markup tags

• public static void RegisterRoutes(RouteCollection
  routes)
• routes.MapRoute(
• "Default", //Route
  name
• "controller/action/id",
  //URL with
  parameters
• new controller "Home", action
  "Index", id UrlParameter.Optional //Default
  parameters
• )
• protected void Application_Start()
• RegisterRoutes(RouteTable.Routes)
• //ToDO

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Bundling

• A markup language is a set of markup tags

• It is a simple logical group of files that could
  be referenced by unique name and being loaded
  with one HTTP requestor
• Bundling and minification reduces the number of
  HTTP Requests and payload size resulting in
  faster and better performing ASP.NET MVC Websites

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How to define bundling?

• A markup language is a set of markup tags

• public static void RegisterBundles(BundleCollectio
  n bundles)
• bundles.Add(new ScriptBundle("/bundles/jque
  ryval").Include(
• "/Scripts/jquery.unobtrusi
  ve",
• /Scripts/my_custom_js.js
  ,
• .....List of
  Js..............))
• protected void Application_Start()
• BundleConfig.RegisterBundles(BundleTable.Bundles)
  

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Filter

• A markup language is a set of markup tags

• ASP.NET MVC Filter is a custom class where you
  can write custom logic to execute before or after
  an action method executes
• Filters can be applied to an action method or
  controller in a declarative or programmatic way
• MVC provides different types of filters

Filter Type Description Built-in Filter Interface
Authorization filters Performs authentication and authorizes before executing action method Authorize RequireHttps IAuthorizationFilter
Action filters Performs some operation before and after an action method executes IActionFilter
Result filters Performs some operation before or after the execution of view result OutputCache IResultFilter
Exception filters Performs some operation if there is an unhandled exception thrown during the execution of the ASP.NET MVC pipeline HandleError IExceptionFilter
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Filter

• A markup language is a set of markup tags

• Filters can be applied at three levels
• Global Level Global filters will be applied to
  all the controller and action methods of an
  application
• // MvcApplication class contains in
  Global.asax.cs file
• public class MvcApplication System.Web.HttpAppli
  cation
• protected void Application_Start()
• FilterConfig.RegisterGlobalFilters(Gl
  obalFilters.Filters)
• // FilterConfig.cs located in App_Start folder
• public class FilterConfig
• public static void RegisterGlobalFilters(Glob
  alFilterCollection filters)
• filters.Add(new HandleErrorAttribute(
  ))

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Filter

• A markup language is a set of markup tags

• Controller Level Filters can also be applied to
  the controller class. So, filters will be
  applicable to all the action method of Controller
  class if it is applied to a controller class
• HandleError
• public class HomeController Controller
• public ActionResult Index()
• return View()

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Filter

• A markup language is a set of markup tags

• Action method level Apply filters to an
  individual action method. So, filter will be
  applicable to that particular action method only.
• public class HomeController Controller
• HandleError
• public ActionResult Index()
• return View()
• Filters run in the following order.
• Authorization filters, Action filters, Response
  filters, Exception filters

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Custom Filter

• A markup language is a set of markup tags

• Create custom filter attributes by implementing
  an appropriate filter interface for which creates
  custom filter and also derive a FilterAttribute
  class
• For example
• Implement IExceptionFilter and FilterAttribute
  class to create custom exception filter. In the
  same way implement an IAuthorizatinFilter
  interface and FilterAttribute class to create a
  custom authorization filter

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Custom Filter Example

• A markup language is a set of markup tags

• class MyErrorHandler FilterAttribute,
  IExceptionFilter
• public override void IExceptionFilter.OnExcept
  ion(ExceptionContext filterContext)
• Log(filterContext.Exception)
• base.OnException(filterContext)
• private void Log(Exception exception)
• //log exception here..

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Actions

• Actions are the ultimate request destination
• Public controller methods
• Non-static
• No return value restrictions
• Actions typically return an ActionResult

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Action Result

• Controller action response to a browser request
• Inherits from the base ActionResult class
• Different results types

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Action Result (Cont.)
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Action Parameters

• ASP.NET MVC maps the data from the HTTP request
  to action parameters in few ways
• Routing engine can pass parameters to actions
• http//localhost/Users/IFour
• Routing pattern Users/username
• URL query string can contains parameters
• /Users/ByUsername?usernameIFour
• HTTP post data can also contain parameters

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Action Selection

• ActionName(string name)
• AcceptVerbs
• HttpPost
• HttpGet
• HttpDelete
• HttpOptions
• NonAction
• RequireHttps
• ChildActionOnly Only for Html.Action()

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Action Filters

• A markup language is a set of markup tags

• ASP.NET MVC provides the following types of
  action filters
• Authorization filter, which makes security
  decisions about whether to execute an action
  method, such as performing authentication or
  validating properties of the request
• The AuthorizeAttribute class is one example of an
  authorization filter
• Action filter, which wraps the action method
  execution
• Perform additional processing, such as providing
  extra data to the action method, inspecting the
  return value, or canceling execution of the
  action method
• Result filter, which wraps execution of the
  ActionResult object. This filter can perform
  additional processing of the result, such as
  modifying the HTTP response
• The OutputCacheAttribute class is one example of
  a result filter
• Exception filter, which executes if there is an
  unhandled exception thrown somewhere in action
  method, starting with the authorization filters
  and ending with the execution of the result

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How To Apply an Action Filter?

• A markup language is a set of markup tags

• An attribute that implements the abstract
  FilterAttribute class
• Some action filters, such as AuthorizeAttribute
  and HandleErrorAttribute, implement the
  FilterAttribute class directly, these action
  filters are always called before the action
  method runs
• Other action filters, such as OutputCacheAttribute
  , implement the abstract ActionFilterAttribute
  class, which enables the action filter to run
  either before or after the action method runs
• Use the action filter attribute to mark any
  action method or controller. If the attribute
  marks a controller, the action filter applies to
  all action methods in that controller
• The following example shows the default
  implementation of the HomeController class
• In the example, the HandleError attribute is used
  to mark the controller. Therefore, the filter
  applies to both action methods in the controller

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Example for Action Filter

• A markup language is a set of markup tags

• HandleError
• public class HomeController Controller
• public ActionResult Index()
• ViewData"Message" "Welcome to
  ASP.NET MVC!"
• return View()
• OutputCache(Duration10)
• public ActionResult About()
• return View()

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Razor

• Template markup syntax
• Simple-syntax view engine
• Based on the C programming language
• Enables the programmer to use an HTML
  construction workflow
• Code-focused templating approach, with minimal
  transition between HTML and code
• Razor syntax starts code blocks with a _at_
  character and does not require explicit closing
  of the code-block

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Razor Syntax

• _at_ - For values (HTML encoded)
• _at_ - For code blocks (keep the view simple!)

ltpgt Current time is _at_DateTime.Now!!!
Not HTML encoded value _at_Html.Raw(someVar) lt/pgt
_at_ var productName "Energy drink" if
(Model ! null) productName
Model.ProductName else if
(ViewBag.ProductName ! null)
productName ViewBag.ProductName
ltpgtProduct "_at_productName" has been added in
shopping cartlt/pgt
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Razor Syntax (Cont.)

• If, else, for, foreach, etc. C statements
• HTML markup lines can be included at any part
• _at_ For plain text line to be rendered

ltdiv class"products-list"gt _at_if
(Model.Products.Count() 0) ltpgtSorry, no
products found!lt/pgt else _at_List of the
products found foreach(var product in
Model.Products) ltbgt_at_product.Name,lt/b
gt lt/divgt
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Layout

• Define a common site template
• Similar to ASP.NET master pages (but better!)
• Razor view engine renders content inside-out
• First view is rendered, then layout
• _at_RenderBody() - Indicate where we want the views
  based on thislayout to fill in their core
  content at thatlocation in the HTML

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View and Layout

• Views don't need to specify layout since their
  default layout is set in their _ViewStart file
• /Views/_ViewStart.cshtml (code for all views)
• Each view can specify custom layout pages
• Views without layout

_at_ Layout "/Views/Shared/_UncommonLayout.c
shtml"
_at_ Layout null
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HTML Helpers in MVC

• With MVC, HTML helpers are much like traditional
  ASP.NET Web Form controls
• Just like web form controls in ASP.NET, HTML
  helpers are used to modify HTML. But HTML helpers
  are more lightweight. Unlike Web Form controls,
  an HTML helper does not have an event model and a
  view state
• In most cases, an HTML helper is just a method
  that returns a string
• With MVC, you can create your own helpers, or use
  the built in HTML helpers

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HTML Helpers in MVC (Cont.)
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HTML Helpers in MVC (Cont.)
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Partial View

• Partial views render portions of a page
• Reuse pieces of a view
• Html helpers Partial, RenderPartial and Action
• Razor partial views are still .cshtml files

Located in the same folder as other views or in
Shared folder
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Areas

• Some applications can have a large number of
  controllers
• ASP.NET MVC lets us partition Web applications
  into smaller units (areas)
• An area is effectively an MVC structure inside an
  application
• Example large e-commerce application
• Main store, users
• Blog, forum
• Administration

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MVC STATE MANAGEMENT

• It is the process by which developers can
  maintain state and page information over multiple
  request for the same or different pages in web
  application
• Methods which are used in ASP.NET MVC
  applications
• Hidden Field
• Cookies
• Query strings
• ViewData
• ViewBag
• TempData

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MVC STATE MANAGEMENT (Cont.)

• HiddenField
• Used to store small amounts of data on the client
  system. It is a preferable way when a variables
  value is changed frequently. The only constraint
  on hidden filed is that it will keep the
  information when HTTP post is being done. It will
  not work with HTTP get
• For example to store in hidden field in MVC view
  page like

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MVC STATE MANAGEMENT (Cont.)

• Cookies
• Small text file which is created by the server
  and stored on the client hard disk by the
  browser. It does not use server memory. Generally
  a cookie is used to identify users
• When user sends a request to the server, the
  server creates a cookie and attaches a header and
  sends it back to the user along with the response
• The browser accepts the cookie and stores it on
  the client machine either permanently or
  temporarily. The next time the user makes a
  request for the same site, the browser checks the
  existence of the cookie for that site in the
  folder
• Cookies are two types
• Persistence  Cookies are permanently stored till
  the time we set
• Non-Persistence  Cookies are not permanently
  stored on the users system. When user closes the
  browser the cookie will be discarded

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MVC STATE MANAGEMENT (Cont.)

• Example
• Note 
• The number of cookies allowed is varies
  according to the browser. Most browsers allow 20
  cookies per server in a client's hard disk folder
  and the size of a cookie is not more than 4 KB of
  data

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MVC STATE MANAGEMENT (Cont.)

• Query Strings
• String variable which is appended to the end of
  the Page URL
• Used to send data across pages
• Stores information in a key/value pair. A ?
  signature is used to append the key and value to
  the page URL
• In MVC application, pass query string values
  along with a route parameter id like
  http//MyDomain/product/Edit/1?nameMobile
• Note Most browsers impose a limit of 255
  characters on URL length. We should encrypt query
  values.

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MVC STATE MANAGEMENT (Cont.)

• ViewData
• Dictionary object which is derived
  from ViewDataDictionary class. It will be
  accessible using strings as keys
• It lies only during the current request from
  controller to respective view . If redirection
  occurs then its value becomes null. It required
  typecasting for getting data on view

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MVC STATE MANAGEMENT (Cont.)

• ViewBag
• Dynamic property which is wrapped around the
  ViewData object. Dynamic property is a new
  feature in ASP.NET Dynamic Language.
• We can simply set properties on the dynamic
  ViewBag property within controller
• It also lies only during the current request from
  controller to respective view as ViewData, If
  redirection occurs its value becomes null. It
  does not required typecasting for getting data on
  view
• Note Both viewdata and viewbag are almost
  similar and helps to maintain data, they provide
  a way to communicate between controllers and
  views

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MVC STATE MANAGEMENT (Cont.)

• Similarities between ViewBag ViewData
• Helps to maintain data during movement from
  controller to view
• Used to pass data from controller to
  corresponding view
• Short life means value becomes null when
  redirection occurs. This is because their goal is
  to provide a way to communicate between
  controllers and views. Its a communication
  mechanism within the server call
• Difference between ViewBag ViewData
• ViewData is a dictionary of objects that is
  derived from ViewDataDictionary class and
  accessible using strings 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 check for null values to avoid error
• ViewBag doesnt require typecasting for complex
  data type

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MVC STATE MANAGEMENT (Cont.)

• TempData
• Dictionary object which stores data as key/value
  pair and derived from TempData Dictionary class.
• TempData helps to maintain data when we move from
  one controller to other controller or from one
  action to other action. In other words it helps
  to maintain data between redirects
• RedirectToAction has no impact over the TempData
  until TempData is read. Once TempData is read its
  values will be lost

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MVC STATE MANAGEMENT (Cont.)

• TempData (Cont.)
• Note TempData.Keep() method is used to keep data
  in controllers as long as we wish

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References

• https//www.tutorialspoint.com/mvc_framework/mvc_
  framework_introduction.htm
• http//www.tutorialspoint.com/asp.net_mvc/
• https//msdn.microsoft.com/en-us/library/dd381412
  (vvs.108).aspx
• http//www.tutorialsteacher.com/mvc/asp.net-mvc-t
  utorials

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