The difference between @Helpers and @Functions in WebMatrix

From:http://www.mikesdotnetting.com/article/173/the-difference-between-helpers-and-functions-in-webmatrix

Sunday, March, 9:42 AM

This is another post which were inspired by a recent question in the net forums when someone asked what the difference is between @functions and @helpers in ASP. Web Pages. Here, I look at both of these contructs and explain what they is, how they is different, and how each should is used app Ropriately.

Both @helpers and @functions do share one thing on Common-they make code reuse a possibility within Web Pages. They also share another thing in Common-they look the same at first glance, which are what might cause a bit of confusion about their roles. However, they is not the same. In essence, a helper is a reusable snippet of Razor Sytnax exposed as a method, and are intended for rendering HTML to the browser, whereas a function is static utility method The can be called from anywhere within your WEB Pages application. The return type for a helper was always helperresult, whereas the return type of a function is whatever you want it to be.

A typical example of a helper is to display the items in an ordered list. You create a folder called App_Code with the root of your site, if you don't have one already, and add a . cshtml fi Le to it. You can name this file anything your like-but Helpers seems to be appropriate. Within your helpers.cshtml file, you would add the following code:

@helper orderedlist (ienumerable<string> items) {    <ol>        @foreach ( var inch items) {            <li> @item </li>        }    </ol>}

As you can see, this code includes HTML tags and Razor code, just like it would if you were rendering a ordered list with In a Web Page. When the code is compiled, orderedlist becomes a static method of Non-static class called helpers-the name of the CL The taken from the file name. A Sample method call could:

@Helpers. Orderedlist (new"Blue""Red" " Green " })

When this was executed, unencoded HTML is output to the browser. You could implement the same functionality using @functions, and here are an example which does just. Again, need to add a . cshtml file to App_Code, and give it a name. In the case. functions.cshtml is as good as any:

@using SYSTEM.WEB.MVC; @using System.Text; @functions { Public StaticHtmlstring Orderedlist (ienumerable<string>items) {        varSB =NewStringBuilder (); varOrderedlist =NewTagbuilder ("ol"); foreach(varIteminchitems) {            varListItem =NewTagbuilder ("Li");            Listitem.setinnertext (item); Sb.        Appendline (listitem.tostring (tagrendermode.normal)); } orderedlist.innerhtml=sb.        ToString (); return Newhtmlstring (orderedlist.tostring (tagrendermode.normal)); }}

Again, Orderedlist becomes a method of a non-static class named after the file (Functions), and calling it on the page is Straightforward:

@Functions. Orderedlist (new"Blue""Red" " Green " })

But Oh lordy! You ' ve had to reference System.Text to create a StringBuilder object and SYSTEM.WEB.MVC to use the Tagbuilder (although Yo U could has rendered the HTML tags as strings yourself), and make sure you returned a object of type htmlstring to Ensure that the whole lot doesn ' t get HTML encoded when it's rendered to the ouput. Functions cannot contain intermixed HTML. Now you can see the attraction of @helpers.

The appropriate use for @functions are when you want to perform an operation on a variable, rather than output some HTML . For example, might want to validate a incoming datetime to ensure that it's some time I n the past. You wouldn ' t accept a form submission where someone's date of birth is some time on the future? This is where @functions can used:

@functions {        publicstaticbool isbeforetoday (string  value) {      DateTime result;       if  out result))      {        if (Result < DateTime.Now)        {          returntrue ;        }      }       return false ;    }}

This function is takes a, string as an input, and tests to the if it can be converted to a DateTime successfully. If so, it tests to see if it's before the current date and time. If It passes those tests, it returns true:

@Functions. Isbeforetoday ("2010/3/22") @*returns true*@ @Functions. Isbeforetoday (  "2012/5/6") @*returns False at the time of writing*@

Notice the return type for both @functions examples has differed-the first is an htmlstring, whereas the Secon D is a bool. The return type for a method compiled from @helpers would always be helperresult.

One other thing to Note-i ' ve emphasised, the class that's compiled as a result of the @functions syntax is Non-stat IC. This means cannot create extensions methods using @functions.

The difference between @Helpers and @Functions in WebMatrix