What is an MvcHtmlString and when should I use it

Question

The documentation for MvcHtmlString is not terribly enlightening      Represents an HTML-encoded string that should not be encoded again    It s not clear to me what exactly the implications of this are  It seems that some HTML helper methods return an MvcHtmlString  but several examples I ve seen online of custom helpers just return a regular string   Questions   What is an MvcHtmlString   When should I choose MvcHtmlString over string and vice versa  Why

User · Answer

This is a late answer but if anyone reading this question is using razor, what you should remember is that razor encodes everything by default, but by using MvcHtmlString in your html helpers you can tell razor that it doesn't need to encode it.

If you want razor to not encode a string use

@Html.Raw("<span>hi</span>")

Decompiling Raw(), shows us that it's wrapping the string in a HtmlString

public IHtmlString Raw(string value) {
    return new HtmlString(value); 
}

"HtmlString only exists in ASP.NET 4.

MvcHtmlString was a compatibility shim added to MVC 2 to support both .NET 3.5 and .NET 4. Now that MVC 3 is .NET 4 only, it's a fairly trivial subclass of HtmlString presumably for MVC 2->3 for source compatibility." source

User · Answer

A nice practical use of this is if you want to make your own HtmlHelper extensions   For example  I hate trying to remember the  lt link gt  tag syntax  so I ve created my own extension method to make a  lt link gt  tag    lt Extension   gt    Public Function CssBlock ByVal html As HtmlHelper  ByVal src As String  ByVal Optional ByVal htmlAttributes As Object   Nothing  As MvcHtmlString     Dim tag   New TagBuilder  link       tag MergeAttribute  type    text css       tag MergeAttribute  rel    stylesheet       tag MergeAttribute  href   src      tag MergeAttributes New RouteValueDictionary htmlAttributes       Dim result   tag ToString TagRenderMode Normal      Return MvcHtmlString Create result  End Function   I could have returned String from this method  but if I had the following would break    lt    Html CssBlock Url Content    sytles mysite css      gt   With MvcHtmlString  using either  lt          gt  or  lt          gt  will both work correctly

User · Answer

You would use an MvcHtmlString if you want to pass raw HTML to an MVC helper method and you don t want the helper method to encode the HTML

User · Answer

ASP NET 4 introduces a new code nugget syntax  lt      gt    Essentially   lt    foo   gt  translates to  lt    HttpUtility HtmlEncode foo    gt    The team is trying to get developers to use  lt      gt  instead of  lt      gt  wherever possible to prevent XSS   However  this introduces the problem that if a code nugget already encodes its result  the  lt      gt  syntax will re-encode it   This is solved by the introduction of the IHtmlString interface  new in  NET 4    If the foo   in  lt    foo     gt  returns an IHtmlString  the  lt      gt  syntax will not re-encode it   MVC 2 s helpers return MvcHtmlString  which on ASP NET 4 implements the interface IHtmlString   Therefore when developers use  lt    Html       gt  in ASP NET 4  the result won t be double-encoded   Edit   An immediate benefit of this new syntax is that your views are a little cleaner   For example  you can write  lt    ViewData  anything     gt  instead of  lt    Html Encode ViewData  anything      gt

[c#] What is an MvcHtmlString and when should I use it?

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