Adding a New Controller

Adding a New Controller

MVC stands for model-view-controller. MVC is a pattern for developing applications that are well architected, testable and easy to maintain. MVC-based applications contain:

Models: Classes that represent the data of the application and that use validation logic to enforce business rules for that data. MV iews: Template files that your application uses to dynamically generate HTML responses. MC ontrollers: Classes that handle incoming browser requests, retrieve model data, and then specify view templates that return a response to the browser.

Let's begin by creating a controller class. In Solution Explorer, right-click the Controllers folder and then click Add, then Controller.

In the Add Scaffold dialog box, click MVC 5 Controller - Empty, and then click Add.

Name your new controller "HelloWorldController" and click Add.

Notice in Solution Explorer that a new file has been created named HelloWorldController.cs and a new folder Views\HelloWorld. The controller is open in the IDE.

Replace the contents of the file with the following code.

The controller methods will return a string of HTML as an example. The controller is named HelloWorldController and the first method is named Index. Let's invoke it from a browser. Run the application (press F5 or Ctrl+F5). In the browser, append "HelloWorld" to the path in the address bar. (For example, in the illustration below, it's http://localhost:1234/HelloWorld.) The page in the browser will look like the following screenshot. In the method above, the code returned a string directly. You told the system to just return some HTML, and it did!

ASP.NET MVC invokes different controller classes (and different action methods within them) depending on the incoming URL. The default URL routing logic used by ASP.NET MVC uses a format like this to determine what code to invoke:

/[Controller]/[ActionName]/[Parameters]

When you run the application and don't supply any URL segments, it defaults to the "Home" controller and the "Index" action method specified in the defaults section of the code above.

The first part of the URL determines the controller class to execute. So /HelloWorld maps to the HelloWorldController class. The second part of the URL determines the action method on the class to execute. So /HelloWorld/Index would cause the Index method of the HelloWorldController class to execute. Notice that we only had to browse to /HelloWorld and the Index method was used by default. This is because a method named Index is the default method that will be called on a controller if one is not explicitly specified. The third part of the URL segment ( Parameters) is for route data.

Browse to http://localhost:xxxx/HelloWorld/Welcome. The Welcome method runs and returns the string "This is the Welcome action method...". The default MVC mapping is /[Controller]/[ActionName]/[Parameters]. For this URL, the controller is HelloWorld and Welcome is the action method. You haven't used the [Parameters] part of the URL yet.

All source collected from https://learn.microsoft.com/en-us/aspnet/mvc/overview/getting-started/introduction/adding-a-controller