Asp.Net Mvc What Is A Controller Complete Guide

What is a Controller in ASP.NET MVC?

A Controller in ASP.NET MVC handles incoming HTTP requests, processes user input, and interacts with the model to perform actions based on that input. It is responsible for selecting which view should be displayed based on the request.

Step-by-Step Guide

Step 1: Create a New ASP.NET MVC Project

1. Open Visual Studio.
2. Go to File > New > Project (or press CTRL + SHIFT + N).
3. Select .NET Core Web or .NET Framework Web depending on your preference.
4. Choose ASP.NET Core Web App (Model-View-Controller) if using .NET Core, or ASP.NET Web Application (.NET Framework) if using .NET Framework, and click Next.
5. Name your project (e.g., MVCFirstApp) and choose a location to save it.
6. Click Create.

Step 2: Add a Controller

1. In the Solution Explorer, right-click on the Controllers folder.
2. Select Add > Controller.
3. Choose MVC Controller - Empty (this template creates a new controller without any views or models). Click Add.
4. Name your controller (e.g., HomeController). Click Add.

Visual Studio will create a new file named HomeController.cs in the Controllers folder. By default, it contains the following code:

using Microsoft.AspNetCore.Mvc;

namespace MVCFirstApp.Controllers
{
    public class HomeController : Controller
    {
        public IActionResult Index()
        {
            return View();
        }
    }
}

If you're using the .NET Framework version, the code will look like this:

using System.Web.Mvc;

namespace MVCFirstApp.Controllers
{
    public class HomeController : Controller
    {
        // GET: Home
        public ActionResult Index()
        {
            return View();
        }
    }
}

Step 3: Understand the Default Controller

• HomeController: The name of the controller. In ASP.NET MVC, the convention is that the class name ends with Controller.
• Index Method: This is an action method. Each public method in a controller class is an action method that can handle a request.
• View Result: The controller returns a View result, indicating that it wants to display the default view associated with this action method (Index.cshtml).

Step 4: Add a View for the Index Action

1. Right-click inside the Index action method in HomeController.
2. Select Add View... from the context menu.
3. In the Add MVC View dialog, make sure the following settings are correct:
   • View name: Index
   • Template: Empty (no layout or master page)
   • Check Create as a partial view if you want to make it a partial view, otherwise leave it unchecked.
4. Click Add.

Visual Studio will create a new view file named Index.cshtml in the Views/Home folder with the following content:

@{
    ViewData["Title"] = "Home Page";
}

<div>
    <h1>Welcome to the MVC First App</h1>
</div>

Step 5: Modify the Controller and View to Add More Functionality

Let's add a new action method to our controller and create a corresponding view.

1. In HomeController.cs, add a new action method called About:

public class HomeController : Controller
{
    public IActionResult Index()
    {
        return View();
    }

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

2. Right-click inside the About action method.
3. Select Add View.
4. In the Add MVC View dialog, set:
   • View name: About
   • Template: Empty
5. Click Add.

Visual Studio will create an About.cshtml file. Modify the contents to display some information:

@{
    ViewData["Title"] = "About Us";
}

<h1>About Us</h1>
<p>This application was created to demonstrate ASP.NET MVC Controllers.</p>

Routing to Actions

By default, ASP.NET Core MVC uses the following route template: {controller=Home}/{action=Index}/{id?}. This means:

• If no controller or action is specified in the URL, it defaults to Home/Index.
• You can access the Index action via http://localhost:YourPort/ or http://localhost:YourPort/Home/Index.
• To access the About action, use http://localhost:YourPort/Home/About.

In .NET Framework MVC applications, routing is configured in the RouteConfig.cs file (found in the App_Start folder). The default route is usually set up like this:

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 }
    );
}

This means the same URLs apply here.

Step 6: Run the Application

1. Press F5 or click Start in Visual Studio.
2. The application will launch in your default web browser.
3. Navigate to http://localhost:YourPort/Home/Index. You should see the "Welcome to the MVC First App" message.
4. Navigate to http://localhost:YourPort/Home/About. You should see the "About Us" message.

Summary

• Controller: A class in the ASP.NET MVC framework that handles incoming HTTP requests and returns appropriate HTTP responses.
• Action Methods: Public methods within a controller class that handle specific requests.
• View: A markup template that an MVC controller uses to generate HTTP responses.
• Routing: The process of mapping URLs to action methods in controllers.