Routing in ASP.NET MVC is a mechanism that maps incoming HTTP requests to specific controller actions. It allows developers to define URL patterns that are user-friendly and SEO-friendly, making it easier for users to navigate the application. Routing is a fundamental part of the ASP.NET MVC framework, as it determines how URLs are processed and which controller and action methods are invoked.

How Routing Works

When a user makes a request to an ASP.NET MVC application, the routing engine examines the URL and matches it against predefined route patterns. If a match is found, the routing engine directs the request to the appropriate controller and action method. The routing process involves the following steps:

1. The user makes an HTTP request to a specific URL.
2. The routing engine checks the URL against the defined routes in the application.
3. If a matching route is found, the routing engine extracts the controller and action names from the URL.
4. The routing engine invokes the specified controller and action method, passing any route parameters as arguments.
5. The action method processes the request and returns a result, which is rendered by the view.

Defining Routes

Routes are defined in the RouteConfig.cs file, which is typically located in the App_Start folder of an ASP.NET MVC application. The RegisterRoutes method is where you can define your application's routes.

        
        using System.Web.Mvc;
        using System.Web.Routing;

        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 }
                );
            }
        }
            

In this example:

• The IgnoreRoute method is used to ignore requests for certain resources, such as Web API routes.
• The MapRoute method defines a route named "Default" that maps URLs in the format /{controller}/{action}/{id}.
• The defaults parameter specifies default values for the controller, action, and id if they are not provided in the URL.

Custom Routes

You can also define custom routes to create more user-friendly URLs. For example, if you want to create a route for a product details page, you can add the following route definition:

        
        routes.MapRoute(
            name: "ProductDetails",
            url: "Product/Details/{id}",
            defaults: new { controller = "Product", action = "Details", id = UrlParameter.Optional }
        );
            

In this example, the URL /Product/Details/5 would route to the Details action of the ProductController, passing 5 as the id parameter.

Route Parameters

Route parameters can be defined in the URL pattern, allowing you to capture values from the URL. For example, in the custom route defined above, {id} is a route parameter that can be accessed in the action method:

        
        public class ProductController : Controller
        {
            public ActionResult Details(int id)
            {
                // Retrieve the product by id and return the view
                var product = GetProductById(id);
                return View(product);
            }
        }
            

Conclusion

In conclusion, routing in ASP.NET MVC is a powerful feature that allows developers to create clean and user-friendly URLs. By defining routes in the RouteConfig.cs file, you can control how incoming requests are processed and which controller actions are invoked. This flexibility enhances the overall user experience and improves the maintainability of the application.