Controllers in ASP.NET MVC Application

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Controllers in ASP.NET MVC Application

In this article, I am going to discuss the Controllers in ASP.NET MVC Application. Please read our previous article before proceeding to this article where we discussed the need and use of ASP.NET MVC Folders and Files which are by default created when we create a new ASP.NET MVC 5 application. As part of this article, we are going to discuss the following pointers which are related to MVC Controllers.

1. What is a Controller in the ASP.NET MVC application?
2. How to Create a Controller in MVC?
3. Understanding Controller with multiple Examples.

What is a Controller in an ASP.NET MVC application?

A controller in an ASP.NET MVC Application is a class having a set of public methods. These public methods of the controller class are called action methods or simple actions. These action methods in the ASP.NET MVC application are going to handle the incoming HTTP Requests.

The Controllers in an ASP.NET MVC application logically group similar types of actions together. This grouping of action together allows us to define sets of rules such as routing, caching, and authorization which is going to be applied collectively. Please have a look at the following diagram for a better understanding of the controller.

As shown in the above diagram, the Controller is the component that is going to receive the incoming HTTP Request and then process that request. While processing the request, the controller does several things. It works with the model. Then it selects a view and if needed then passes the model object to the view. The view then generates the necessary HTML and the controller then sends the HTML back to the client who initially made the request. So we can consider that the Controller is the heart of the MVC application.

By convention, in ASP.NET MVC, the controller classes should reside in the project’s root level Controllers folder and should be inherited from the System.Web.Mvc.Controller base class.

Let’s understand the Controllers in ASP.NET MVC application with an example.

Creating an Empty ASP.NET MVC application:

Open Visual Studio and select File => New => Project as shown in the image below.

Once you click on the “Project” link a new dialog will pop up. From that New Project window, from the left pane select Web template under the Visual C# which is under the “Installed – Templates” section. From the middle pane select ASP.NET Web Application and give the name of your project as FirstMVCDemo. Finally, click on the OK button as shown in the image below.

Once you click on the OK button, then a new dialog window will open with the name New ASP.NET Web Application for selecting the Project Templates. From this window, we are going to select the Empty project template as we are going to do everything from scratch. Finally, click on the OK button as shown in the below image.

Once we click on the OK button, it will take some time to create the project with the empty template with the following default folder structure.

As you can see in the above image, the project is created with several folders such as Models, Views, Controllers, etc. As the names suggest these folders are going to contain Models, Views, and Controllers respectively. We will discuss Models and Views in our upcoming article and in this article, we are going to focus on the Controllers.

Adding Controller to the Project:

To add a controller to your project follow the below steps

1. Right Click on the “Controllers” folder
2. Select Add > Controller
3. Select MVC 5 Controller – Empty
4. Click on the ADD button as shown in the image below

Once you click on the Add button, then a new pop-up window will open where you need to provide a name for your controller. Set the Controller Name as HomeController and click on the Add button as shown in the image below.

Once you click on the Add button, then you should have HomeController.cs within the “Controllers” folder as shown in the below image.

At this point, if you run your application, then you will get the following error.

Fixing the Error:

In order to fix the above error, we need to add a view with the name “Index”. We will discuss views in detail in our next article. So here we will fix the above issue in another way. The following is the function that is auto-generated by the HomeController class.

namespace FirstMVCDemo.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            return View();
        }
    }
}

namespace FirstMVCDemo.Controllers
{
    public class HomeController : Controller
    {
        public string Index()
        {
            return "Hello MVC 5 Application";
        }
    }
}

using System.Web.Mvc;
namespace FirstMVCDemo.Controllers
{
    public class HomeController : Controller
    {
        public string Index(string id, string name)
        {
            return "The value of  Id = " + id + " and Name = " + name;
        }
    }
}

using System.Web.Mvc;
namespace FirstMVCDemo.Controllers
{
    public class HomeController : Controller
    {
        public string Index(string id, string name)
        {
            return "Id = " + id + " ,Name = " + Request.QueryString["name"];
        }
    }
}