How to create a function in a cshtml template?

Question

I need to create a function that is only necessary inside one cshtml file. You can think of my situation as ASP.NET page methods, which are min web services implemented in a page, because they're scoped to one page. I know about HTML helpers (extension methods), but my function is just needed in one cshtml file. I don't know how to create a function signature inside a view. Note: I'm using Razor template engine.

Folliculin

See also The Difference Between Helpers and Functions – Ovarian

Answer 1

You can use the @helper Razor directive:

@helper WelcomeMessage(string username)
{
    <p>Welcome, @username.</p>
}

Then you invoke it like this:

@WelcomeMessage("John Smith")

Shennashensi

You can't put tags inside the @functions methods, so I like this answer. – Neuman

Yes this is much better than declaring a function. Much more straight forward. – Airscrew

But you can't return variables (hence the word function) – Vernissage

@Vernissage I don't understand what you mean by that. – Shennashensi

I was just commenting that I don't think @helper could return a variable. It just renders markup/razor. When I read OP's post I thought he needed to return a variable but maybe not. – Vernissage

Got it. You mean @helper cannot return values other than IHtmlString. That is correct. @helper is like a specialized function which is optimized for returning HTML (i.e. it does HTML encoding automatically, whereas plain functions do not.) – Shennashensi

Does asp.net core also support the @helper ? – Sacco

@Sacco no it doesn't. You can find alternatives listed in this article What Happened To Helper In ASP.NET Core? – Vexillum

For aspnet core, see Migrate html helpers to ASP.NET Core or the other answers in this post – Transpose

Answer 2

why not just declare that function inside the cshtml file?

@functions{
    public string GetSomeString(){
        return string.Empty;
    }
}

<h2>index</h2>
@GetSomeString()

Diabolize

This should be marked as the answer, as the @functions directive specifically meets the OP requirements. The Helpers feature is intended for shared use across multiple template files by putting the file with the @helper directive into an App_Code directory. Whereas, the @functions directive allows a function to be used only by the template that declares it. – Kochi

I didn't want to say anything but the OP did say "but my function is just needed in one cshtml file" - my answer obv does exactly that where as the marked answer does not. – Diabolize

@stimpy77 Can you provide a source for "The Helpers feature is intended for shared use across multiple template files"? See ASP.NET MVC 3 and the helper syntax within Razor in ScottGu's Blog. – Shennashensi

o.O your own link is rather explicit. "Reusing helpers across multiple views" "we can define the helper method outside of our view template, and enable it to be re-used across all of the view templates in our project" blah blah blah – Kochi

@stimpy77 Let's try that again: "Alternatively, we can define the Helper method outside of our view template..." (ScottGu) - "The Helpers feature is intended for shared use across multiple template..." (you) The "Alternatively" part (that you conveniently left out of Scott's quote) and the "intended" part (that you unnecessarily added to yours) are the key. We normally use eggs for cooking. The fact that we can alternatively use them for going egging doesn't mean that they are intended for it, or that we shouldn't use eggs for making breakfast. – Shennashensi

Daniel, you argue the semantics of "alternatively" but I find it highly doubtful that ScottGu has a background in being a lawyer. He was clearly taking a step-by-step tutorial approach to instruction of best practices, leading up to the end goal. Everything about the article appears to me to be formatted to suggest that the whole point of the feature is to enable its reuse. Futher, semantically, a "helper" is in fact a utility feature that is by definition intended to be reused, not a function to be used in an isolate context. I leave you to your opinion and ask that we agree to disagree. – Kochi

i agree with stimpy77 - i also agree that the OP had asked for a way to show a means to have a"function that is only necessary inside one cshtml file". if you have globally available methods that aren't needed outside of the scope of a single use - then your API will be rendered unusable. – Diabolize

Also note helpers seem oriented to returning strings just like other razor helpers already do, and thus the functions solution provides more flexibility for toher return types. Both answers get +1 in my book though as they are both useful tidbits of info. – Bradshaw

@Bradshaw Agreed. Using functions also gives you the option of making functions private, unlike helpers. – Fete

@Bradshaw To be fair, helpers don't return strings but IHtmlString, which take care of HTML encoding for you and protect your app from XSS attacks. Helpers also give you the convenience of Razor syntax in the helper itself, which you lose with functions. In other words, <p>Welcome, @username.</p> versus return new HtmlString("<p>Welcome, " + Html.Encode(username) + ".</p>");. – Shennashensi

@Daniel +1 Good to know. There definitely isn't a best. Each provides a different type of flexibility depending on what you want to accomplish. – Bradshaw

using @helper in a single view doesn't make it available to other views, though. the reason I like @helper better is you can put html between your curly braces. @functions doesn't (easily) let you do that. – Neuman

Just for the record: both @helper and @functions can be shared among many views, and both can be declared into and used by a single view (and I have personally found use for them in both shared/single scenarios). IMHO the only practical difference between them is the fact that a view helper adds syntactic sugar for returning rendered HTML snippets (or, more appropriate, HelperResult instances), while a view function is usually only useful for returning simple reference or value types. – Peacock

how can I use the function defined in another file? – Hemicrania

@GeorgiKovachev put them in the App_Code directory and they are globaly available – Diabolize

Answer 3

If your method doesn't have to return html and has to do something else then you can use a lambda instead of helper method in Razor

@{
    ViewBag.Title = "Index";
    Layout = "~/Views/Shared/_Layout.cshtml";

    Func<int,int,int> Sum = (a, b) => a + b;
}

<h2>Index</h2>

@Sum(3,4)

Anchoveta

It is useful though if you need to access page's global variables in your function, is there an other way to do so ? :/ – Dissever

Answer 4

Take a look at Declarative Razor Helpers

Demetrademetre

Answer 5

In ASP.NET Core Razor Pages, you can combine C# and HTML in the function:

@model PagerModel
@{
}

@functions 
{
    void PagerNumber(int pageNumber, int currentPage)
    {
        if (pageNumber == currentPage)
        {
            <span class="page-number-current">@pageNumber</span>
        }
        else
        {
            <a class="page-number-other" href="/table/@pageNumber">@pageNumber</a>
        }
    }
}

<p>@PagerNumber(1,2) @PagerNumber(2,2) @PagerNumber(3,2)</p>

Acetum

Answer 6

If you want to access your page's global variables, you can do so:

@{
    ViewData["Title"] = "Home Page";

    var LoadingButtons = Model.ToDictionary(person => person, person => false);

    string GetLoadingState (string person) => LoadingButtons[person] ? "is-loading" : string.Empty;
}

Dissever

Since C# 7.0 this is the only proper and correct answer. GetLoadingState() here is local function. – Gasaway