Looking for guide line about Razor syntax in asp.net mvc

Question

i am learning asp.net mvc just going through online tutorial

1) just see <span>@model.Message</span> and @Html.Raw(model.Message)

suppose if "Hello Word" is stored in Message then "Hello Word" should display if i write statement like <span>@model.Message</span> but i just could not understand what is the special purpose about @Html.Raw(model.Message). what @Html.Raw() will render ?

please discuss with few more example to understand the difference well.

2) just see the below two snippet

@if (foo) {
  <text>Plain Text</text> 
}

@if (foo) {
  @:Plain Text is @bar
}

in which version of html the tag called was introduce. is it equivalent to

or what ? what is the purpose of this tag ?

just tell me about this @:Plain Text is @bar what is the special meaning of @: ? if our intention is to mixing text with expression then can't we write like Plain Text is @bar

3) <span>ISBN@(isbnNumber)</span> what it will print ? if 2000 is stored in isbnNumber variable then it may print <span>ISBN2000</span>. am i right ?

so tell me what is the special meaning of @(variable-name) why bracket along with @ symbol ?

4) just see

<span>In Razor, you use the 
@@foo to display the value 
of foo</span>

if foo has value called god then what this @@foo will print ?

5 ) see this and guide me about few more syntax given below point wise

a) @(MyClass.MyMethod<AType>())

b)

@{
  Func<dynamic, object> b = 
   @<strong>@item</strong>;
}
@b("Bold this")

c) <div class="@className foo bar"></div>

6) see this

@functions
{
string SayWithFunction(string message)
{
return message;
}
}
@helper SayWithHelper(string message)
{

Text: @message

}
@SayWithFunction("Hello, world!")
@SayWithHelper("Hello, world!")

what they are trying to declare ? function ? what kind of syntax it is ? it seems that two function has been declare in two different way ? please explain this points with more sample. thanks

Few More question

7)

@{
  Func<dynamic, object> b = @<strong>@item</strong>;
}
<span>This sentence is @b("In Bold").</span>

what the meaning of above line ? is it anonymous delegate? when some one will call @b("In Bold") then what will happen ?

8) @{ var items = new[] { "one", "two", "three" }; }

<ul>
@items.List(@<li>@item</li>)
</ul>

tell me something about List() function and from where the item variable come ?

9)

@{
    var comics = new[] { 
        new ComicBook {Title = "Groo", Publisher = "Dark Horse Comics"},
        new ComicBook {Title = "Spiderman", Publisher = "Marvel"}
    };
}

<table>
@comics.List(
  @<tr>
    <td>@item.Title</td>
    <td>@item.Publisher</td>
  </tr>)
</table>

please explain briefly the above code. thanks

Answer 1

1.

By default, Razor automatically html-encodes your output values (<div> becomes <div>). @Html.Raw should be used when you explicitly want to output the value as-is without any encoding (very common for outputting JSON strings in the middle of a <script>).

---

2.

The purpose of <text> and @: is to escape the regular Razor syntax flow and output literal text values. for example:

// i just want to print "Haz It" if some condition is true
@if (Model.HasSomething) { Haz It } // syntax error
@if (Model.HasSomething) { <text>Haz It</text> } // just fine

As of @:, it begins a text literal until the next line-feed (enter), so:

@if (Model.HasSomething) { @:Haz It } // syntax error, no closing '}' encountered

// just fine
@if (Model.HasSomething)
{
    @:Haz It
}

---

3.

By default, if your @ is inside a quote/double-quotes (<tr id="row@item.Id"), Razor interprets it as a literal and will not try to parse it as expression (for obvious reasons), but sometimes you do want it to, then you simply write <tr id="row@(item.Id").

---

4.

The purpose of @@ is simply to escape '@'. when you want to output '@' and don't want Razor to interpret is as an expression. then in your case @@foo would print '@foo'.

---

5.

a. @(MyClass.MyMethod<AType>()) would simply output the return value of the method (using ToString() if necessary).

b. Yes, Razor does let you define some kind of inline functions, but usually you better use Html Helpers / Functions / DisplayTemplates (as follows).

c. See above.

---

6.

As of Razor Helpers, see http://weblogs.asp.net/scottgu/archive/2011/05/12/asp-net-mvc-3-and-the-helper-syntax-within-razor.aspx

Answer 2

1) Any kind of @Variable output makes MVC automatically encode the value. That is to say if foo = "Joe & Dave", then @foo becomes Joe & Dave automatically. To escape this behavior you have @Html.Raw.

2) <text></text> is there to help you when the parser is having trouble. You have to keep in mind Razor goes in and out of HTML/Code using the semantics of the languages. that is to say, it knows it's in HTML using the XML parser, and when it's in C#/VB by its syntax (like braces or Then..End respectively). When you want to stray from this format, you can use <text>. e.g.

<ul>
    <li>
        @foreach (var item in items) {
          @item.Description
          <text></li><li></text>
        }
    </li>
</ul>

Here you're messing with the parser because it no longer conforms to "standard" HTML blocks. The </li> would through razor for a loop, but because it's wrapped in <text></text> it has a more definitive way of knowing where code ends and HTML begins.

3) Yes, the parenthesis are there to help give the parser an explicit definition of what should be executed. Razor makes its best attempt to understand what you're trying to output, but sometimes it's off. The parenthesis solve this. e.g.

@Foo.bar

If you only had @Foo defined as a string, Razor would inevitably try to look for a bar property because it follows C#'s naming convention (this would be a very valid notation in C#, but not our intent). So, to avoid it from continuing on we can use parenthesis:

@(Foo).bar

A notable exception to this is when there is a single trailing period. e.g.

Hello, @name.

The Razor parser realizes nothing valid (in terms of the language) follows, so it just outputs name and a period thereafter.

4) @@ is the escape method for razor when you need to actually print @. So, in your example, you'd see @foo on the page in plain text. This is useful when outputting email addresses directly on the page, e.g.

bchristie@@contoso.com

Now razor won't look for a contoso.com variable.

5) You're seeing various shortcuts and usages of how you bounce between valid C# code and HTML. Remember that you can go between, and the HTML you're seeing is really just a compiled IHtmlString that is finally output to the buffer.