ASP.NET MVC and ASP.NET Web Forms are both frameworks for building web applications, but they follow different architectural patterns and design philosophies. Below are the key differences between the two:

1. Architectural Pattern

ASP.NET MVC: Follows the Model-View-Controller (MVC) pattern, which separates the application into three main components: Model, View, and Controller. This separation promotes a clean architecture and makes the application easier to manage and test.

ASP.NET Web Forms: Uses a page-based architecture where each page is a self-contained unit. It relies heavily on server-side controls and events, which can lead to a tightly coupled design.

2. State Management

ASP.NET MVC: Does not maintain state automatically. Developers have to manage state explicitly, which can lead to more efficient applications, especially for large-scale systems.

ASP.NET Web Forms: Automatically maintains state through ViewState, which can increase the size of the page and affect performance.

3. Control Over HTML

ASP.NET MVC: Provides full control over the generated HTML. Developers can write clean, semantic HTML, which is beneficial for SEO and responsive design.

ASP.NET Web Forms: Generates HTML based on server-side controls, which can lead to complex and less readable HTML markup.

4. Testability

ASP.NET MVC: Designed with testability in mind. The separation of concerns allows for easier unit testing of controllers and models.

ASP.NET Web Forms: The tightly coupled nature of the framework makes unit testing more challenging.

5. Routing

ASP.NET MVC: Uses a powerful routing engine that allows for clean and SEO-friendly URLs. Developers can define custom routes easily.

ASP.NET Web Forms: Uses a more traditional approach with file-based routing, which can lead to less friendly URLs.

Sample Code Comparison

ASP.NET MVC Example

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

In the above MVC example, the HomeController defines an Index action that returns a view. The routing engine maps the URL to this action.

ASP.NET Web Forms Example

        
        public partial class Home : System.Web.UI.Page
        {
            protected void Page_Load(object sender, EventArgs e)
            {
                if (!IsPostBack)
                {
                    // Initialization code here
                }
            }
        }
            

In the Web Forms example, the Home page is a self-contained unit with a Page_Load event. The page lifecycle is managed by the framework, which can lead to more complex state management.

Conclusion

In summary, ASP.NET MVC and ASP.NET Web Forms serve different purposes and cater to different development styles. ASP.NET MVC is more suited for developers looking for control, testability, and a clean architecture, while ASP.NET Web Forms may appeal to those who prefer a rapid development model with built-in state management.