05 - Razor Views

Views in ASP.NET Core MVC

• In the Model-View-Controller (MVC) pattern, the view encapsulates the presentation details of the user's interaction with the app.
• Views are HTML templates with embedded code that generate content to send to the client.
• Views use Razor syntax, which allows code to interact with HTML with minimal code or ceremony.

View files

• Views use .cshtml extension
• Are located in web project – Views folder
• Typically, each controller has its own folder within Views folder
• Typically, every action has its own view
  \Views\<ControllerName>\<ActionName>.cshtml
• Shared views are in folder \Views\Shared
• In addition to action specific views there are
  • partial views
  • layouts,
  • special view files
  • ...

Specify what view file to use

• Usually just return View() or return View(viewModel) is used
• View discovery process (unless concrete view is requested)
  \Views\<ControllerName>\<ActionName>.cshtml
\Views\Shared\<ActionName>.cshtml
• Returning some specific view
  

  return View(“ViewName”,viewModel); // cshtml extension not required
  return View(“/Views/CustomViews/ViewName.cshtml”,viewModel);
  

Passing data

Two widely used methods

• Using ViewModels (DTOs) (can be cpecific objects or domain objects)
  • strongly typed – intellisense, compiler errors
  • strongly recommended (required in this course!)
• Using ViewBag or ViewData
  • loosely typed data, no compiler support
  • erros can only be dicovered during runtime

Passing data - ViewModel

• return view(viewModel);
• In view file specify model class
  @model ModelType and access it with @Model
• ViewModels are strongly typed, with full IntelliSense support. Views are precompiled by default on distribution build.

@model Domain.Person
<h2>Info</h2>
<div>
    @Model.FirstName<br /> 
    @Model.LastName<br />
</div>

Passing data - loosely typed

• ViewData or ViewBag - collection of data (objects)
• Accessible both in action methods and in views
• ViewData – string based dictionary
  

  ViewData["key"] = someObject;
  

• ViewBag – dynamic object collection
  

  ViewBag.otherKey = fooObject;
  

• ViewBag uses ViewData for its actual object storage.
  So you can mix and match them.

  ViewData["foo"] = "bar";
  ViewBag.foo = ViewBag.foo + "barbar";
  

• No intellisense support, needs casting (except strings)

Razor syntax

• Razor is markup syntax for embedding server based code into web pages.
• Razor syntax – Razor markup, C# code and HTML
• Default language in razor is HTML
• @ symbol is used to transiton from HTML into C#
• Razor expressions – any output is rendered to html output
  
  
• Implicit – generally spaces are not allowed

<div>@DateTime.Now</div>
<div>@DoSomething("Hello", "World")</div>

• Explicit - @(...C#...) - spaces are ok

<div>@(DateTime.Now - TimeSpan.FromDays(7))</div

Expression encoding

• C# expressions in Razor are converted to string foobar.ToString() and encoded.
• If C# expressions evaluates to IHtmlContent, then it is not converted and rendered directly
• Use html Raw helper to write out unencoded content

@Html.Raw("<span>Hello World</span>")

Razor code blocks

• @{ ... c# statement; ... }
• Default language in code block is C#
• Using html inside code block transitions language back to html

@{
    var inCSharp = true;
    <p>Now in HTML, was in C# @inCSharp</p>
}

• Explicit transition to html
• Use razor <text></text> tags
• Single line transition - @:

@for (var i = 0; i < people.Length; i++)
{
    var person = people[i];
    @:Name: @person.Name
}

Control structures

• Conditionals
  • @if, else if, else
  • @switch

@if (value % 2 == 0)
{
    <p>The value was even</p>
}
else if (value >= 1337)
{
    <p>The value is large.</p>
}
else
{
    <p>The value was not large and is odd.</p>
}

• Looping
  • @for
  • @foreach
  • @while
  • @do while
• Compound
  • @using

@using (Html.BeginForm())
{
    <div>
        email:
        <input type="email" id="Email" name="Email" value="" />
        <button type="submit"> Register </button>
    </div>
}

Comments in razor

• Razor supports C# and HTML comments.

@{
    /* C# comment. */
    // Another C# comment.
}
<!-- HTML comment -->

• Razor comments @* ... *@

 @*
    @{
        /* C# comment. */
        // Another C# comment.
    }
    <!-- HTML comment -->
*@

Razor directives

A directive will typically change the way a page is parsed or enable different functionality within your Razor page.

• @using
• @model
• @inherits
• @inject
• @functions
• @section
• @page

Directives

Vies are transformed into C# code/classes and compiled

@{
    var output = "Hello World";
}
<div>Output: @output</div>

Directives add some modifications into generated C# code

public class _Views_Something_cshtml : RazorPage<dynamic>
{
    public override async Task ExecuteAsync()
    {
        var output = "Hello World";

        WriteLiteral("/r/n<div>Output: ");
        Write(output);
        WriteLiteral("</div>");
    }
}

• @using System.IO
  adds using to the generated code

• @model SomeModelType
  public class_Views_Test_cshtml : RazorPage<SomeModelType>

• @inject
  Enables you to inject a service from your service container into your Razor page for use.

• @section
  used in conjunction with the layout page to enable views to render content in different parts of the rendered HTML page.

• @functions { // C# Code }

@functions {
    public string GetHello()
    {
        return "Hello";
    }
}

<div>From method: @GetHello()</div> 
~~~~

~~~csharp
public class _Views_Home_Test_cshtml : RazorPage<dynamic>
{
    public string GetHello()
    {
        return "Hello";
    }
    public override async Task ExecuteAsync()
    {
       x
        Write(GetHello());
        WriteLiteral("</div>\r\n");
    }
...

Layout

Most web apps have a common layout that provides the user with a consistent experience as they navigate from page to page.

Default layout

• Default layout is located at
  Views\Shared\_Layout.cshtml

• Specifying an layout

  • Can use partial name or full path

• Every layout must call RenderBody()
  Wherever RenderBody() is called, contents of the view will be rendered.

@{
    Layout = "_Layout";
}

Section

• Defining placeholder in layout file
  @RenderSection("Scripts", required: false)

• Then define the section in view

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

Shared directives

Directives can be placed in file
_ViewImports.cshtml

Supports only these:

• @addTagHelper
• @removeTagHelper
• @tagHelperPrefix
• @using
• @model
• @inherits

Views\_ViewImports.cshtml is shared location for all views

@using WebApp
@using WebApp.Models.AccountViewModels
@using WebApp.Models.ManageViewModels
@using Microsoft.AspNetCore.Identity
@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers

Initial code

• Place initial code in
  _ViewStart.cshtml
• Included in front of every view
• Hierarchical, like _ViewImports
• These are included in order, starting from the /View, then from /Controller

@{
    Layout = "_Layout";
}

Partial views

A partial view is a view that is rendered within another view. The HTML output generated by executing the partial view is rendered into the calling (or parent) view.

Partial views do not include _ViewStart.cshtml

Partial tag helper.

<partial name="_PartialName" />
<partial name="_PartialName"  for="Model" view-data="ViewData"/>
<partial name="_PartialName"  model="Model" view-data="ViewData"/>

• for
  • assigns model expression
• model
  • assigns model instance
• view-data
  • assigns ViewDataDictionary

Older, html helper partial.

@Html.Partial("SomePartialView")
@await Html.PartialAsync("SomePartialViewWithAsyncCode")

@{
    Html.RenderPartial("SomePartialView ");
    Html.RenderPartialAsync("SomePartialViewWithAsyncCode ");
}

Partial view discovery

/Areas/<Area-Name>/Views/<Controller-Name>
/Areas/<Area-Name>/Views/Shared
/Views/Shared
/Pages/Shared

Partial views can be chained—a partial view can call another partial view if a circular reference isn't formed by the calls. Relative paths are always relative to the current file, not to the root or parent of the file.

Area

• Areas are used to organize related functionality into a group as a separate namespace (for routing) and folder structure (for views).
• Using areas creates a hierarchy for the purpose of routing by adding another route parameter, area, to controller and action.
• Effectively a separate MVC structure inside an web application

Folder structure

Typical folder structure

WebApp

• Areas
  • Admin
    • Controllers
    • Views
    • Models
  • Client
    • Controllers
    • Views
    • Models

/Areas/<Area-Name>/Views/<Controller-Name>/<Action-Name>.cshtml
/Areas/<Area-Name>/Views/Shared/<Action-Name>.cshtml
/Views/Shared/<Action-Name>.cshtml

Area controllers

• Structure of views folder is important – compiled singly. Controllers and models can be anywhere – one dll.
• Assign controller to specific area using area attribute

namespace MyStore.Areas.Admin.Controllers;

[Area("Admin")]
public class HomeController : Controller {
    ...
}

Area routing

Set up convention-based routing

app.MapControllerRoute(
    name: "areas",
    pattern: "{area:exists}/{controller=Home}/{action=Index}/{id?}");

Area links

Inside the same are - no action needed, ambient value is used

To different area

<a asp-area="Admin" asp-controller="Home" asp-action="Index">Admin</a>

To no area

<a asp-area="" asp-controller="Home" asp-action="Index">Home</a>