MS - ASP.NET MVC

Here we'll talk about ASP.NET MVC, can be build either thru .NET Framework or .NET Core

Project Structure:




0). MVC Versions & Features:

• MVC 1.0 | VS2008 |.Net 3.5 | 13-Mar-2009
• MVC architecture with webform engine
• Routing
• HTML Helpers
• Ajax Helpers
• Auto binding
• MVC 2.0 | VS 2008 |.Net 3.5/4.0 | 10-Mar-2010
• Area
• Asynchronous controller
• Html helper methods with lambda expression
• DataAnnotations attributes
• Client side validation
• Custom template
• Scaffolding  
• Templated Helpers  
• Html.ValidationSummary Helper Method
• DefaultValueAttribute in Action-Method Parameters
• Binding Binary Data with Model Binders
• Model-Validator Providers
• New RequireHttpsAttribute Action Filter
• Templated Helpers
• Display Model-Level Errors
• MVC 3.0 | VS 2010 | .Net 4.0 | 13-Jan-2011
• Unobtrusive javascript validation
• Razor view engine
• Global filters
• Remote validation
• Dependency resolver for IoC
• ViewBag
• HTML 5 enabled templates
• Model Validation Improvements
• MVC 4.0 | VS 2010 - 2012 | .NET 4.0/4.5 | 15-Aug-2012 
• Mobile project template
• Bundling and minification
• Support for Windows Azure SDK
• ASP.NET Web API
• Enhanced support for asynchronous methods
• MVC 5.0 | VS 2013 |.NET 4.5 | 17-oct-2013
• Authentication filters
• Bootstrap support
• New scaffolding items
• ASP.Net Identity
• Attribute based routing
• Filter overrides
• MVC 5.2 | VS 2013 |.NET 4.5 | 28-Aug-2014
• Attribute based routing
• Bug fixes and minor features update
• MVC 6
• ASP.NET MVC and Web API has been merged in to one.
• Dependency injection is inbuilt and part of MVC.
• Side by side - Deploy the runtime and framework with your application
• Everything packaged with NuGet, Including the .NET runtime itself.
• New JSON based project structure.
• No need to recompile for every change. Just hit save and refresh the browser.
• Compilation done with the new Roslyn real-time compiler.
• vNext is Open Source via the .NET Foundation and is taking public contributions.
• vNext (and Rosyln) also runs on Mono, on both Mac and Linux today.

1) Define Default Routing in MVC?
- This is defined in App_Start/RouteConfig.cs

public class RouteConfig
    {
        public static void RegisterRoutes(RouteCollection routes)
        {
            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

            routes.MapRoute(
                name: "Default",
                url: "{controller}/{action}/{id}",
                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
            );
        }
    }

2) Define Custom Routing in MVC to handle incoming requests that look like this: /Archive/12-25-2009
- This is defined in App_Start/RouteConfig.cs

public class RouteConfig
    {
        public static void RegisterRoutes(RouteCollection routes)
        {
            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

routes.MapRoute(
name: "Blog", // Route name
url:  "Archive/{entryDate}", // URL with parameters
defaults: new { controller = "Archive", action = "Entry" } // Parameter defaults
);


            routes.MapRoute(
                name: "Default",
                url: "{controller}/{action}/{id}",
                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
            );
        }
    }

public class ArchiveController : Controller
{
public string Entry(DateTime entryDate)
{
   return "You requested the entry from " + entryDate.ToString();
}
}


3) Define Routing Constraints in MVC ?
- In above custom route, url ‘/Archive/apple’ will produce error - Because the Entry() action expects an DateTime parameter
- To avoid this make a constraint – when defining a route to restrict the URLs that match the route.
- This constraint causes the Archive route to not to match the URL -  ‘/Archive/apple’ and so no error at runtime.

public class RouteConfig
    {
        public static void RegisterRoutes(RouteCollection routes)
        {
            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

routes.MapRoute(
name: "Blog", // Route name
url:  "Archive/{entryDate}", // URL with parameters
defaults: new { controller = "Archive", action = "Entry" }, // Parameter defaults
new { entryDate = @"\d{2} - \d{2} - \d{4}" }
);


            routes.MapRoute(
                name: "Default",
                url: "{controller}/{action}/{id}",
                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
            );
        }
    }

4). How to prevent a Public Action Method from Being Invoked
- Use [NonAction] attribute.
- Any attempt to invoke such controller action will result into an error message

namespace MvcApplication1.Controllers
{
public class BookController : Controller
{
[NonAction]
public ActionResult Index()
{
return View();           
}
}
}

5). What are different Action Results ?
- A controller action returns something called an Action Result, in response to a browser request.
- ASP.NET MVC supports several types of action results including below (inherit from the base ActionResult class)

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

- In most cases, a controller action returns a ViewResult. When an action returns a ViewResult, HTML is returned to the browser.
- However the ViewResults is not returned directly. Instead, you call one of the following methods of the Controller base class to return the ViewResult.

1. View – Returns a ViewResult action result.
2. Redirect – Returns a RedirectResult action result.
3. RedirectToAction – Returns a RedirectToRouteResult action result.
4. RedirectToRoute – Returns a RedirectToRouteResult action result.
5. Json – Returns a JsonResult action result.
6. JavaScriptResult – Returns a JavaScriptResult.
7. Content – Returns a ContentResult action result.
8. File – Returns a FileContentResult, FilePathResult, or FileStreamResult depending on the parameters passed to the method.

6). What are HTML Helpers in MVC ?

- An HTML Helper is just a method that returns a string. The string can represent any type of content that you want.
- Below are few standard HTML Helpers (this is not a complete list):

- Html.ActionLink()
- Html.BeginForm()
- Html.CheckBox()
- Html.DropDownList()
- Html.EndForm()
- Html.Hidden()
- Html.ListBox()
- Html.Password()
- Html.RadioButton()
- Html.TextArea()
- Html.TextBox()


7). What are Filters in MVC ?
- The ASP.NET MVC framework supports four different types of filters:

• Authorization filters -
• Implements IAuthorizationFilter attribute.
• Used to implement authentication and authorization for controller actions

• Action filters
• Implements  IActionFilter attribute.
• Contain logic that is executed before and after a controller action executes.
• You can use an action filter, for instance, to modify the view data that a controller action returns.
• Few Action filters:
• OutputCache – This action filter caches the output of a controller action for a specified amount of time.
• HandleError – This action filter handles errors raised when a controller action executes.
• Authorize – This action filter enables you to restrict access to a particular user or role.

• Result filters
• Implements IResultFilter attribute.
• Contains logic that is executed before and after a view result is executed.
• For example, you might want to modify a view result right before the view is rendered to the browser.

• Exception filters
• Implements IExceptionFilter attribute
• Used to handle errors raised by either your controller actions or controller action results.
• You also can use exception filters to log errors.

- Base class for all action filters is the System.Web.Mvc.FilterAttribute class.

• To implement a particular type of filter, Then
• You need to create a class that inherits from the Base Filter class (e.g. ActionFilterAttribute) and
• Implements one or more of the IAuthorizationFilter, IActionFilter, IResultFilter, or ExceptionFilter interfaces.

namespace MvcApplication1.ActionFilters
{
public class LogActionFilter : ActionFilterAttribute
{
  public override void OnActionExecuting(ActionExecutingContext filterContext)
  {
   Log("OnActionExecuting", filterContext.RouteData);     
  }

  public override void OnActionExecuted(ActionExecutedContext filterContext)
  {
   Log("OnActionExecuted", filterContext.RouteData);     
  }

  public override void OnResultExecuting(ResultExecutingContext filterContext)
  {
   Log("OnResultExecuting", filterContext.RouteData);     
  }

  public override void OnResultExecuted(ResultExecutedContext filterContext)
  {
   Log("OnResultExecuted", filterContext.RouteData);     
  }

  private void Log(string methodName, RouteData routeData)
  {
   var controllerName = routeData.Values["controller"];
   var actionName = routeData.Values["action"];
   var message = String.Format("{0} controller:{1} action:{2}", methodName, controllerName, actionName);
   Debug.WriteLine(message, "Action Filter Log");
  }

}
}

- Usage:
namespace MvcApplication1.Controllers
{
[LogActionFilter]
public class HomeController : Controller
{
  public ActionResult Index()
  {
   return View();
  }

  public ActionResult About()
  {
   return View();
  }
}
}

8). What is Output Caching in MVC?
- Achieved thru OutputCache Action Filter
- Uses to caches the output of a controller action for a specified amount of time.
- Cache the content returned by any controller method so same content does not need to be generated each time the same controller method is invoked.
- Reduces server round trips, reduces database server round trips, reduces network traffic, etc.


9). What is MVC Application Life Cycle?
- 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 includes four basic steps:

• Step 1: Fill route
• Step 2: Fetch route
• Step 3: Request context created
• Step 4: Controller instance created

10).Understanding the MVC Application Execution Process (C#)
- This is standard - Module Followed By Handler

• Requests first pass thru UrlRoutingModule object, which is an HTTP module.
• This module parses request and performs route selection. I.e Selects first Route Object that matches current request.
•   (A route object is a class that implements RouteBase, and is typically an instance of the Route class.)  

• From selected Route object, module obtains IRouteHandler object (MvcRouteHandler) that is associated with the Route object.
• The IRouteHandler instance creates an IHttpHandler object (MvcHandler) and passes it the IHttpContext object.
• This MvcHandler object then selects the controller that will ultimately handle the request.

11).What are different ways to store data like in Sessions
- ViewBag
- ViewData
- TempData

• TempData - https://www.codeproject.com/Articles/786603/Using-TempData-in-ASP-NET-MVC
• It's a dictionary object derived from TempDataDictionary.
• TempData stays for a subsequent HTTP Request as opposed to other options (ViewBag and ViewData) those stay only for current request.
• So, TempdData can be used to maintain data between controller actions as well as redirects.
• An important thing about TempData is that it stores contents in Session object.
• Diff With Session - TempData gets destroyed immediately after it’s used in subsequent HTTP request, so no explicit action required.

12).What is Validation Summary ? (https://www.aspsnippets.com/Articles/Display-Validation-Summary-in-ASPNet-MVC.aspx)

• Generates an unordered list (UL element) of validation messages that are in the Model State Dictionary object.
• Can be used to display all the error messages for all the fields.
• Also can also be used to display custom error messages - For this you need to add custom errors into the ModelState in the appropriate action method
• ModelState.AddModelError(string.Empty, "Student Name already exists.");
• https://www.tutorialsteacher.com/mvc/htmlhelper-validationsummary

 

Hope this helps...

Arun Manglick