Question

I am writing my own HtmlHelper extenstion for ASP.NET MVC:

public static string CreateDialogLink (this HtmlHelper htmlHelper, string linkText,                                        string contentPath)         {             // fix up content path if the user supplied a path beginning with '~'             contentPath = Url.Content(contentPath);  // doesn't work (see below for why)              // create the link and return it             // .....         }; 

Where I am having trouble is tryin to access UrlHelper from within my HtmlHelper’s definition. The problem is that the way you normally access HtmlHelper (via Html.MethodName(...) ) is via a property on the View. This isn’t available to me obviously from with my own extension class.

This is the actual MVC source code for ViewMasterPage (as of Beta) – which defines Html and Url.

public class ViewMasterPage : MasterPage     {         public ViewMasterPage();          public AjaxHelper Ajax { get; }         public HtmlHelper Html { get; }         public object Model { get; }         public TempDataDictionary TempData { get; }         public UrlHelper Url { get; }         public ViewContext ViewContext { get; }         public ViewDataDictionary ViewData { get; }         public HtmlTextWriter Writer { get; }     } 

I want to be able to access these properties inside an HtmlHelper.

The best I’ve come up with is this (insert at beginning of CreateDialogLink method)

HtmlHelper Html = new HtmlHelper(htmlHelper.ViewContext, htmlHelper.ViewDataContainer); UrlHelper Url = new UrlHelper(htmlHelper.ViewContext.RequestContext); 

Am I missing some other way to access the existing HtmlHelper and UrlHelper instances – or do i really need to create a new one? I’m sure there isn’t much overhead but I’d prefer to use the preexisting ones if I can.

Answer 1

Before asking this question I had looked at some of the MVC source code, but evidently I missed this, which is how they do it for the Image helper.

[System.Diagnostics.CodeAnalysis.SuppressMessage('Microsoft.Design', 'CA1054:UriParametersShouldNotBeStrings', MessageId = '1#', Justification = 'The return value is not a regular URL since it may contain ~/ ASP.NET-specific characters')]         public static string Image(this HtmlHelper helper, string imageRelativeUrl, string alt, IDictionary<string, object> htmlAttributes) {             if (String.IsNullOrEmpty(imageRelativeUrl)) {                 throw new ArgumentException(MvcResources.Common_NullOrEmpty, 'imageRelativeUrl');             }              UrlHelper url = new UrlHelper(helper.ViewContext);             string imageUrl = url.Content(imageRelativeUrl);             return Image(imageUrl, alt, htmlAttributes).ToString(TagRenderMode.SelfClosing);         } 

Looks like instantiating a new UrlHelper is the correct approach after all. Thats good enough for me.

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Update: RTM code from ASP.NET MVC v1.0 Source Code is slightly different as pointed out in the comments.

File: MVC\src\MvcFutures\Mvc\ImageExtensions.cs

 [System.Diagnostics.CodeAnalysis.SuppressMessage('Microsoft.Design', 'CA1054:UriParametersShouldNotBeStrings', MessageId = '1#', Justification = 'The return value is not a regular URL since it may contain ~/ ASP.NET-specific characters')]         public static string Image(this HtmlHelper helper, string imageRelativeUrl, string alt, IDictionary<string, object> htmlAttributes) {             if (String.IsNullOrEmpty(imageRelativeUrl)) {                 throw new ArgumentException(MvcResources.Common_NullOrEmpty, 'imageRelativeUrl');             }              UrlHelper url = new UrlHelper(helper.ViewContext.RequestContext);             string imageUrl = url.Content(imageRelativeUrl);             return Image(imageUrl, alt, htmlAttributes).ToString(TagRenderMode.SelfClosing);         }