A controller does the job of receiving the request and producing the output based on the input data in ASP.NET MVC. You can imagine controllers as the entrance point to your business flow that organizes the application flow.

At the high level, the controller orchestrates between the model and the view, and sends the output back to the user. This is also the place where authentication is usually done through action filters. Action filters are basically interceptors and will be discussed in detail in the Filters section of this chapter. The following diagram illustrates the high-level flow...

The routing engine is responsible for getting the incoming request and routing that request to the appropriate controller based on the URL pattern. We can configure the routing engine so that it can choose the appropriate controller based on the relevant information. In other words, routing is a programmatic mapping that states which method of which controller is to be invoked based on some URL pattern.

By convention, ASP.NET MVC follows this pattern: Controller/Action/Id.

If the user types the URL http://yourwebsite.com/Hello/Greeting/1, the routing engine selects the Hello controller class and Greeting action method within the Hello controller, and passes the Id value as 1. XXXController is a naming convention and it is assumed your controllers are always ending with a controller suffix. You can give default values to some of the parameters and make some...

We'll straight away jump to installing the ASP.NET Core NuGet package in your application.

Follow these steps to install the NuGet package of ASP.NET MVC:

1. Right-click on the dependencies, and select the Manage NuGet Packages option:

2. We will see that a package called Microsoft.ASPNetCore.All is installed (as shown in the following screenshot). This package is actually a meta package that installs most of the dependencies we need.

3. If we extend this package from dependencies, we will see:

So, everything we need is already installed regardless of using an empty project or not.

ASP.NET Core is installed in our application. Now, we need to tell our application to use ASP.NET MVC.

This needs a couple of changes to the Startup.cs file:

1. Configure the application to add the MVC service. This can be done by adding...

Before creating the controller, we need to remove the following app.Run statement as this will return Hello World! for all the incoming requests. As we want incoming requests to be handled by the controllers, we need to remove the following code from the Configure method of the Startup class:

app.Run(async (context) =>
{
  await context.Response.WriteAsync("Hello World!");
};

We have installed ASP.NET Core in our application. So, we are geared up for creating our first ASP.NET Core controller. Create a folder with the name Controllers and add a new controller from the context menu, as shown in the following screenshot:

Context basically represents the request-response pair along with other metadata necessary to process the request. 

So far, we were returning a simple string from the controller. Although that explains the concept of how the Controller and action methods works, it is not of much practical use.

Let's create a new action method named, Index2:

public IActionResult Index2()
{
  return View(); // View for this 'Index2' action method
}

Now, we have created the action method that returns a view, but we have still not added the view. By convention, ASP.NET MVC would try to search for our view in the Views\{ControllerName}\{ActionMethod.cshtml} folder. With respect to the preceding example, it will try to search for Views\Home\Index2.cshtml. Please note that the name of the controller folder is Home, not HomeController. The prefix is only needed as per convention. As this folder structure and file are not available, you&apos...

Models represent your business domain classes. Now, we are going to learn about how to use the Models in our controller. Create a Models folder and add a simple Employee class. This is a just a plain old C# class:

public class Employee
{
  public int EmployeeId { get; set; }
  public string Name { get; set; }
  public string Designation { get; set; }
}

Create a new action method, Employee, in our HomeController, and create an object of the Employee Model with some values, and pass the Model to the View. Our idea is to use the Model employee values in the View to present them to the user:

public IActionResult Employee()
{
  //Sample Model - Usually this comes from database
  Employee emp1 = new Employee
  {
    EmployeeId = 1,
    Name = "Jon Skeet",
    Designation = ...