Part 79 - Areas in asp.net mvc

we will discuss Areas.

When you create a new asp.net mvc application, the following folders are created with in the root directory.
1. Models
2. Views
3. Controllers

This structure is fine for simple applications, but when your application gets big and complex, maintaining your Models, Views and Controllers can get complicated.

The structure of a complex asp.net mvc application can be very easily maintained using areas. So, in short areas are introduced in asp.net mvc 2, that allow us to breakdown a large complex application into a several small sections called areas. These areas can have their own set of
1. Models
2. Views
3. Controllers
4. Routes



Let's understand this with an example. Let's say, we are building a Job Portal. It's common for a typical job portal to have the following functional areas.
Employee Area - This functional area allows a job seeker to create their profile, upload resume, and perform job search.
Employer Area - This functional area allows a job provider to create employer profile, upload jobs, and search for suitable candidates.
Administrator Area - This functional area allows an administrator to configure the site and mantain.

To create an area in an MVC application
1. Right click on the project name in Solution Explorer and select Add => Area
2. Provide a meaningful name. For example "Employee" and click Add

At this point, "Areas" folder will be created, and with in this, a folder for Employee area will be added. You can add as many areas as you want.

In a similar fashion, add areas for Employer and Admin. At this point, your solution explorer should look as shown below. Notice the Areas folder.


Notice that in each area folder (Employee, Employer and Admin), you have a set of Models, Views and Controllers folders. Also, there is "AreaRegistration.cs" file, which contains the code to register a route for the area.

Now navigate to Global.asax.cs file and notice Application_Start(). With in this method there is code to register all areas in your application.
protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();
    WebApiConfig.Register(GlobalConfiguration.Configuration);
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);
}

At this point Add "HomeController" to the following areas. Notice that we can have a HomeController(Controller with the same) in Employee, Employer, Admin and MainArea.
1. Employee
2. Employer
3. Admin
4. Main Area

At this point, we have Index() action method in all of the HomeControllers.
public ActionResult Index()
{
    return View();
}

Now Add Index view to all the areas. Copy and paste the following HTML in respective Index views.
Main Area: <h1>Main Area Index View</h1>
Employee Area: <h1>Employee Area Index View</h1>
Employer Area: <h1>Employer Area Index View</h1>
Admin Area: <h1>Admin Area Index View</h1>

At this point, build the application, and navigate to http://localhost/MVCDemo. You will get an error
Multiple types were found that match the controller named 'Home'. This can happen if the route that services this request ('{controller}/{action}/{id}') does not specify namespaces to search for a controller that matches the request. If this is the case, register this route by calling an overload of the 'MapRoute' method that takes a 'namespaces' parameter.

The request for 'Home' has found the following matching controllers:
MVCDemo.Controllers.HomeController
MVCDemo.Areas.Admin.Controllers.HomeController
MVCDemo.Areas.Employee.Controllers.HomeController
MVCDemo.Areas.Employer.Controllers.HomeController

To fix this change RegisterRoutes() method in RouteConfig.cs file in App_start folder. Notice that we are passing the namespace of the HomeController in the Main area using namespace parameter.
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 },
        namespaces: new [] { "MVCDemo.Controllers" }
    );
}

Now, if you navigate to http://localhost/MVCDemo/Employee, you will get an error - The resource cannot be found.

To fix this, change RegisterArea() area method in EmployeeAreaRegistration.cs file in Employee folder as shown below. Notice that we are setting HomeController as the default controller
public override void RegisterArea(AreaRegistrationContext context)
{
    context.MapRoute(
        "Employee_default",
        "Employee/{controller}/{action}/{id}",
        new { controller = "Home", action = "Index", id = UrlParameter.Optional }
    );
}

Navigating to http://localhost/MVCDemo/Employee may throw a compilation error related to System.Web.Optimization. If you get this error follow the steps below.
1. In Visual Studio, click Tools - Library PAckage Manager - Package Manager Console
2. In the Package Manager Console window, type the following command and press enter
Install-Package Microsoft.Web.Optimization -Pre

When we are building links using ActionLink() html helper to navigate between areas, we need to specify area name as shown below. Copy and paste the following code in all the Index views in all the areas and you will be able to navigate between areas when you click on the respective links.
<table border="1">
    <tr>
        <td>
            <b>Links</b>
        </td>
    </tr>
    <tr>
        <td>
            @Html.ActionLink("Main Area Home Page", "Index", "Home", new { area = "" }, null)
        </td>
    </tr>
    <tr>
        <td>
            @Html.ActionLink("Employee Area Home Page", "Index", "Home", new { area = "Employee" }, null)
        </td>
    </tr>
    <tr>
        <td>
            @Html.ActionLink("Employer Area Home Page", "Index", "Home", new { area = "Employer" }, null)
        </td>
    </tr>
    <tr>
        <td>
            @Html.ActionLink("Admin Area Home Page", "Index", "Home", new { area = "Admin" }, null)
        </td>
    </tr>
</table>