Action method

In this section, you will learn about the action method of the controller class.

All the public methods of the Controller class are called Action methods. They are like any other normal methods with the following restrictions:

1. Action method must be public. It cannot be private or protected
2. Action method cannot be overloaded
3. Action method cannot be a static method.

The following illustrates the Index() action method in the StudentController class.

As you can see in the above figure, the Index() method is public, and it returns the ActionResult using the View() method. The View() method is defined in the Controller base class, which returns the appropriate ActionResult.

Default Action Method

Every controller can have a default action method as per the configured route in the RouteConfig class. By default, the Index() method is a default action method for any controller, as per configured default root, as shown below.

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

However, you can change the default action name as per your requirement in the RouteConfig class.

ActionResult

MVC framework includes various Result classes, which can be returned from an action method. The result classes represent different types of responses, such as HTML, file, string, JSON, javascript, etc. The following table lists all the result classes available in ASP.NET MVC.

The ActionResult class is a base class of all the above result classes, so it can be the return type of action method that returns any result listed above. However, you can specify the appropriate result class as a return type of action method.

The Index() method of the StudentController in the above figure uses the View() method to return a ViewResult (which is derived from the ActionResult class). The base Controller class includes the View() method along with other methods that return a particular type of result, as shown in the below table.

As you can see in the above table, the View() method returns the ViewResult, the Content() method returns a string, the File() method returns the content of a file, and so on. Use different methods mentioned in the above table to return a different type of result from an action method.

Action Method Parameters

Every action methods can have input parameters as normal methods. It can be primitive data type or complex type parameters, as shown below.

[HttpPost]
public ActionResult Edit(Student std)
{
    // update student to the database
    
    return RedirectToAction("Index");
}

[HttpDelete]
public ActionResult Delete(int id)
{
    // delete student from the database whose id matches with specified id

    return RedirectToAction("Index");
}

Please note that action method paramter can be Nullable Type.

By default, the values for action method parameters are retrieved from the request's data collection. The data collection includes name/values pairs for form data or query string values or cookie values. Model binding in ASP.NET MVC automatically maps the URL query string or form data collection to the action method parameters if both names match. Visit model binding section for more information on it.

Points to Remember :

1. All the public methods in the Controller class are called Action methods.
2. The Action method has the following restrictions.
       - Action method must be public. It cannot be private or protected.
       - Action method cannot be overloaded.
       - Action method cannot be a static method.
   
3. ActionResult is a base class of all the result type which returns from Action method.
4. The base Controller class contains methods that returns appropriate result type e.g. View(), Content(), File(), JavaScript() etc.
5. The Action method can include Nullable type parameters.