Asp.Net Mvc Creating Controllers Complete Guide

ASP.NET MVC Creating Controllers

Understanding Controllers A Controller class in ASP.NET MVC is derived from the Controller base class and serves as the main processing unit for HTTP requests. Each controller can contain multiple action methods, which map to specific routes. When a URL that matches a route configured in the application’s RouteConfig is requested, ASP.NET creates an instance of the corresponding Controller and calls the specified action method.

Creating a New Controller You can create Controllers in ASP.NET MVC using Visual Studio’s built-in wizards or manually writing the code.

1. Using Visual Studio Wizard:

   • Open your project.
   • Right-click on the Controllers folder in Solution Explorer.
   • Select Add > Controller.
   • Choose the type of Controller you want to create (e.g., MVC 5 Controller with read/write actions, Empty MVC Controller).
   • Provide the name of the Controller (ensure it ends with 'Controller').
   • Click Add.

2. Manual Code Creation:

   • In the Controllers folder, add a new C# class file.
   • Name it appropriately, ending with 'Controller'.
   • Ensure the class inherits from System.Web.Mvc.Controller.

public class HomeController : Controller
{
    // Action Methods go here
}

Action Methods Action methods are public methods within a Controller class that map to specific HTTP requests. They return an instance of ActionResult, which indicates what response should be sent back to the client. Common types of ActionResult include ViewResult, ContentResult, JsonResult, and RedirectResult among others.

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

public ActionResult About()
{
    ViewBag.Message = "Your application description page.";

    return View();
}

HTTP Request Handling ASP.NET MVC uses routing to forward HTTP requests to the appropriate controller and action method. Routing rules are defined in the RouteConfig class, usually located under the App_Start folder.

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

In the above example, if no controller or action is specified in the URL, it defaults to redirecting to the Home Controller’s Index action method.

Attributes for Mapping You can use attributes above the action method declarations to explicitly define the mapping between URLs and action methods.

• [HttpGet] and [HttpPost]: These specify that the action method should only respond to GET and POST HTTP requests respectively.
• [Route("your-route-pattern")]: This specifies a custom route pattern for the action method.

Example:

[HttpGet]
public ActionResult Login()
{
    return View();
}

[HttpPost]
public ActionResult Login(UserModel model)
{
    if (ModelState.IsValid)
    {
        // Validation logic here
        return RedirectToAction("Index", "Home");
    }

    return View(model);
}

ActionResult Types Controllers can return different types of ActionResults depending on the requirements of the action method.

• ViewResult: Used when you want to render a view.
• PartialViewResult: Renders a partial view.
• RedirectResult: Redirects the browser to a URL.
• RedirectToRouteResult: Redirects the browser using routing rules.
• ContentResult: Returns a plain text string.
• JsonResult: Serializes data into JSON format and sends it back to the client.
• FileResult: Sends binary content back to the client.

Example:

public ActionResult Download()
{
    byte[] fileBytes = System.IO.File.ReadAllBytes(Server.MapPath("~/App_Data/sample.pdf"));
    string fileName = "sample.pdf";
    return File(fileBytes, System.Net.Mime.MediaTypeNames.Application.Pdf, fileName);
}

public JsonResult GetItemsList()
{
    var items = db.Items.ToList();
    return Json(items, JsonRequestBehavior.AllowGet);
}

Dependency Injection Controllers support dependency injection, allowing you to inject services and other dependencies via constructor injection.

Example:

public class UserController : Controller
{
    private readonly IUserService _userService;

    public UserController(IUserService userService)
    {
        _userService = userService;
    }

    public ActionResult Profile(int id)
    {
        var user = _userService.GetUserById(id);
        // Further processing...

        return View(user);
    }
}

Conclusion Creating Controllers in ASP.NET MVC involves several key steps, including defining route mappings, creating action methods, and choosing appropriate ActionResult types based on the response requirements. Understanding these concepts helps in building efficient and robust MVC applications.

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