MVC - Controllers

Hi, here we will discuss about controllers. Please watch Creating Sample MVC application before proceeding. 

There, we discussed that, the URL - http://localhost/Sample_MVC/Home/Index will invoke Index() function of HomeControllerclass. 

Hence you may get a query, where is this mapping defined. The mapping is defined in Global.asax. Notice that in Global.asax we have RegisterRoutes() method. 
RouteConfig.RegisterRoutes(RouteTable.Routes); 



Right click on this method, and select "Go to Definition". Notice the implementation of RegisterRoutes() method in RouteConfig class. This method has got a default route.
public static void RegisterRoutes(RouteCollection routes)
{
    routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

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

The following URL does not have id. This is not a problem because id is optional in the default route.
http://localhost/MVCDemo/Home/Index

Now pass id in the URL as shown below and press enter. Nothing happens.
http://localhost/MVCDemo/Home/Index/10

Change the Index() function in HomeController as shown below.
public string Index(string id)
{
    return "The value of Id = " + id;
}

Enter the following URL and press enter. We get the output as expected.
http://localhost/Sample_MVC/Home/Index/10

In the following URL, 10 is the value for id parameter and we also have a query string"name".
http://localhost/MVC_Sample/home/index/10?name=Pragim

Change the Index() function in HomeController as shown below, to read both the parameter values.
public string Index(string id, string username)
{
    return "The value of Id = " + id + " and Name = " + username;
}

Just like web forms, you can also use "Request.QueryString"
public string Index(string id)
{
    return "The value of Id = " + id + " and Name = " + Request.QueryString["username"];
}