I have decided to write a series of posts on how to write a small ASP.Net MVC 4.0 application.I will develop this application step by step and I will explain everything that you need to know in order to develop ASP.Net MVC 4.0 applications. This is the fourth post in this series. You can find the first one here , the second one here and the third one here. Make sure you read and understand those posts.

I am building an ASP.Net MVC application where users can enter movies and rate them. As we develop our application I will change the requirements and add more features. My goal is to have a working application and at the same time show you the building blocks of ASP.Net MVC. In the last post we have created the entities needed in order to store and retrieve data (models,views and the database).

Now I would like to talk about Code Blocks and Code Expressions in Razor Views.

1) Launch Visual Studio and open the ASP.Net MVC application

2)  Open the Index.cshtml from the Views/Movie folder.These are the contents of the view

@model IEnumerable<MovieReviews.Models.Μovie>

@{
    ViewBag.Title = "Index";
    var reviewscount = Model.Count();
}

<h2>Index</h2>

<h3>the number of the reviews so far is : @reviewscount </h3>

<p>
    @Html.ActionLink("Create New", "Create")
</p>
<table>
    <tr>
        <th>
            @Html.DisplayNameFor(model => model.Name)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Director)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.YearReleased)
        </th>
        <th></th>
    </tr>

@foreach (var item in Model) {
    <tr>
        <td>
            @Html.DisplayFor(modelItem => item.Name)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.Director)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.YearReleased)
        </td>
        <td>
            @Html.ActionLink("Edit", "Edit", new { id=item.Id }) |
            @Html.ActionLink("Details", "Details", new { id=item.Id }) |
            @Html.ActionLink("Delete", "Delete", new { id=item.Id })
        </td>
    </tr>
}

</table>
 

The responsibility of this view is to take the model passed by the controller and present the data to the users through the template. The View is nothing more than a template where the data passed from the model is presented.We combine literal text (e.g <h2></h2>) with pieces of data from the model through C# code (@).

Code Expressions

An example of code expressions from the view above

         <td>
            @Html.DisplayFor(modelItem => item.Name)
        </td>

 The code in bold is a code expression.The code expression will be evaluated by the Razor engine and the output (which will be displayed in a column of an html table) will be presented to the client.

Code blocks

An example of code block from the view above

 @

{
    ViewBag.Title = "Index";

}

Between the curly braces we can add as much C# code as we want.Let me modify a little bit the View above

@{
    ViewBag.Title = "Index";
    var reviewscount = Model.Count();
}

<h2>Index</h2>

<h3> the number of the reviews so far is : @reviewscount </h3>

The code I changed is in bold.Run your application again http://localhost:59871/movie (http://localhost:yourport/movie) in your case.

I added a new variable inside the code block and then used the variable (reviewscount) in a place I wanted inside the view as a code expression. Hope all makes sense so far.

3) Now I would like to point out at this point are HTML Helpers that are part of any View in the ASP.Net MVC applications.Their purpose is to create small blocks of HTML.There are helpers like to create links,inputs,labels,forms,validation messages and much more.

Think of them like traditional ASP.NET Web Form controls.

We use HTML helpers are used to modify HTML.  HTML helpers do not have an event model and a view state.

In most cases, an HTML helper is just a method that returns a string.

Let's have a look at the

• Html.ActionLink()

   @Html.ActionLink("Edit", "Edit", new { id=item.Id }) |

 This is the easiest way to render an HTML link

The Html.ActionLink() does not link to a view. It creates a link to a controller action.

You also can see more HTML Helpers in the View

• Html.DisplayNameFor()  - which Gets the display name for the model
• Html.DisplayFor() will render the DisplayTemplate that matches the property's type

There are more HTML helpers can be used to render (modify and output) HTML form elements:

• BeginForm()
• EndForm()
• TextArea()
• TextBox()
• ValidationMessageFor()
  

We will see more of those as we move on.

3)  When you run your application and navigate to the http://localhost:59871/movie you see HTML elements that are not in the current view (Index view).

I mean the navigation system (menu) the header,logo and the footer.Where does this markup come from? It comes form the Layout View.Υοu can think of this as the master pages in web forms applications.

Have a look at the picture below to see what I mean

Have a look in the Shared folder in the Solution Explorer. You will see the_Layout.cshtml.

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8" />
        <title>@ViewBag.Title - My ASP.NET MVC Application</title>
        <link href="~/favicon.ico" rel="shortcut icon" type="image/x-icon" />
        <meta name="viewport" content="width=device-width" />
        @Styles.Render("~/Content/css")
        @Scripts.Render("~/bundles/modernizr")
    </head>
    <body>
        <header>
            <div class="content-wrapper">
                <div class="float-left">
                    <p class="site-title">@Html.ActionLink("your logo here", "Index", "Home")</p>
                </div>
                <div class="float-right">
                    <section id="login">
                        @Html.Partial("_LoginPartial")
                    </section>
                    <nav>
                        <ul id="menu">
                            <li>@Html.ActionLink("Home", "Index", "Home")</li>
                            <li>@Html.ActionLink("About", "About", "Home")</li>
                            <li>@Html.ActionLink("Contact", "Contact", "Home")</li>
                        </ul>
                    </nav>
                </div>
            </div>
        </header>
        <div id="body">
            @RenderSection("featured", required: false)
            <section class="content-wrapper main-content clear-fix">
                @RenderBody()
            </section>
        </div>
        <footer>
            <div class="content-wrapper">
                <div class="float-left">
                    <p>&copy; @DateTime.Now.Year - My ASP.NET MVC Application</p>
                </div>
            </div>
        </footer>

        @Scripts.Render("~/bundles/jquery")
        @RenderSection("scripts", required: false)
    </body>
</html>
 

We have the head section that will be present in all pages

    <head>
        <meta charset="utf-8" />
        <title>@ViewBag.Title - My ASP.NET MVC Application</title>
        <link href="~/favicon.ico" rel="shortcut icon" type="image/x-icon" />
        <meta name="viewport" content="width=device-width" />
        @Styles.Render("~/Content/css")
        @Scripts.Render("~/bundles/modernizr")
    </head>

Then you have the header section that will appear in all pages

        <header>
            <div class="content-wrapper">
                <div class="float-left">
                    <p class="site-title">@Html.ActionLink("your logo here", "Index", "Home")</p>
                </div>
                <div class="float-right">
                    <section id="login">
                        @Html.Partial("_LoginPartial")
                    </section>
                    <nav>
                        <ul id="menu">
                            <li>@Html.ActionLink("Home", "Index", "Home")</li>
                            <li>@Html.ActionLink("About", "About", "Home")</li>
                            <li>@Html.ActionLink("Contact", "Contact", "Home")</li>
                        </ul>
                    </nav>
                </div>
            </div>
        </header>

Then you have the header section that will appear in all pages

  <footer>
            <div class="content-wrapper">
                <div class="float-left">
                    <p>&copy; @DateTime.Now.Year - My ASP.NET MVC Application</p>
                </div>
            </div>
        </footer>

At one point we see a call to the RenderBody()

    <div id="body">
            @RenderSection("featured", required: false)
            <section class="content-wrapper main-content clear-fix">
                @RenderBody()
            </section>

 When the Layout View calls RenderBody(), that is when the content View (index.cshtml) will be inserted and rendered at this exact point in the HTML markup.

 How does ASP.Net MVC to call the Layout View before our content View? It is because of this file _ViewStart.cshtml

The contents of the _ViewStart.cshtml follow

@{
    Layout = "~/Views/Shared/_Layout.cshtml";
}

ASP.Net MVC runtime knows to render first the Layout View (because the _ViewStart.cshtml runs first before any other view ) and then the Content View.

4) Another important topic in ASP.Net MVC applications are Partial Views.At some point in the _Layout.cshtml view there is a call to the _LoginPartial partial view.

                    <section id="login">
                        @Html.Partial("_LoginPartial")
                    </section>

A partial view is a view that we place code (HTML & C#) that we will often reuse in other views..

Have a look at the contents of the _LoginPartial.cshtml

@if (Request.IsAuthenticated) {
    <text>
        Hello, @Html.ActionLink(User.Identity.Name, "Manage", "Account", routeValues: null, htmlAttributes: new { @class = "username", title = "Manage" })!
        @using (Html.BeginForm("LogOff", "Account", FormMethod.Post, new { id = "logoutForm" })) {
            @Html.AntiForgeryToken()
            <a href="javascript:document.getElementById('logoutForm').submit()">Log off</a>
        }
    </text>
} else {
    <ul>
        <li>@Html.ActionLink("Register", "Register", "Account", routeValues: null, htmlAttributes: new { id = "registerLink" })</li>
        <li>@Html.ActionLink("Log in", "Login", "Account", routeValues: null, htmlAttributes: new { id = "loginLink" })</li>
    </ul>
}
 

So this is a type of special View that we must know and use so we make our application easier to maintain.

5) Now it is time to have a look at some important topics that are related with Controllers.Open the MovieController.cs file.

I would like to talk a bit about ActionResults and what thet are

The ActionResult is an abstract base class for other types of actions.

Other classes inheriting from the ActionResult :

• ContentResult
• EmptyResult
• FileResult
• HttpStatusCodeResult
• JavaScriptResult
• RedirectResult
• RedirectToRouteResult
• ViewResult

The ViewResult renders a specifed view to the client.

The ContentResult writes content to the client without requiring a view.

In this method Index() the result of this method is ActionResult , which means we will call the Index.cshtml (passing the model to it) in the Views/Movie folder.

So the results of this view will be displayed to the client.

  private MovieDBContext db = new MovieDBContext();

        //
        // GET: /Movie/

        public ActionResult Index()
        {
            return View(db.Movies.ToList());
        }

Another very important topic is Action Selectors.Some of them are ActionName, AcceptVerbs.

An ActionSelector dictates which action method is triggered.They come with the form of attributes.

Have a look at the MovieController.cs file and the Delete method

        [HttpPost, ActionName("Delete")]

        public ActionResult DeleteConfirmed(int id)
        {
            Μovie μovie = db.Movies.Find(id);
            db.Movies.Remove(μovie);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

ActionName  will specify the name of this method. It can be reached by Delete and not DeleteConfirmed

AcceptVerbs (HttpPost,HttpGet) represent attributes that specify which HTTP verbs (Get , Post) an action method will respond to.

In the example above we have an HTTP Post - [HttpPost, ActionName("Delete")]

The final topic I would like to talk about is Action Filters. They are applied to methods and classes in the form of attributes.An ActionFilter provides some methods that are run before and after request and response processing.

Some of them are

• OutputCache, which caches the output of the controller
• Authorize, that restricts an action to authorized users or roles

If I open the MovieController.cs file and then apply the [Authorize] (see below)  to the  Index() method

      private MovieDBContext db = new MovieDBContext();

        //
        // GET: /Movie/

        [Authorize]

        public ActionResult Index()
        {
            return View(db.Movies.ToList());
        }

and then navigate to the http://localhost:59871/movie, this is what I will get the following as a result (redirect to the login page)

The ASP.Net MVC runtime will pick up the [Authorize] attribute and redirect me to the Login page.

Hope you have followed along and mastered the topics presented here as they are absolutely necessary for building ASP.Net MVC applications. 

In the next post we will continue building our application.

Hope it helps!!!