Access HttpContext in ASP.NET Core

[Richard Deeming]

asp.net core - how to get IUrlHelper from inside Html helper - Stack Overflow[^] Correcting the typo in that answer gives:

public static IHtmlContent CHGridTable<TModel>(this IHtmlHelper<TModel> htmlHelper, DataTable dt, object htmlAttributes = null)
{
var urlHelperFactory = (IUrlHelperFactory)htmlHelper.ViewContext.HttpContext.RequestServices.GetService(typeof(IUrlHelperFactory));
var urlHelper = urlHelperFactory.GetUrlHelper(htmlHelper.ViewContext);
string urlEdit = url.RouteUrl("Default");
...
}

You might also want to consider whether a custom tag helper might be a better choice for what you're trying to do: Tag Helpers in ASP.NET Core | Microsoft Docs[^]

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"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

[Vincent Maverick Durano]

Hmm.. it's really hard to test it out without a dev machine. Anyway instead of passing IHttpContextAccessor, try to pass the IActionContextAccessor instead. For example in your Helper class, you can do:

private static IActionContextAccessor \_actionContextAccessor;
private static IUrlHelperFactory \_urlHelperFactory;
public static void SetHttpContextAccessor(IActionContextAccessor accessor, IUrlHelperFactory urlHelperFactory) {
    \_actionContextAccessor = accessor;
    \_urlHelperFactory = urlHelperFactory;
}

then you can do:

var urlHelper = _urlHelperFactory.GetUrlHelper(_actionContextAccessor.ActionContext);

and finally, configure the IActionContextAccessor in Startup.ConfigureServices method:

var accessor = serviceProvider.GetService()
var userHelperFactory = serviceProvider.GetService()
HtmlHelperExt.SetHttpContextAccessor(accessor,userHelperFactory);

You could also try what's suggested by Richard.

[JimFeng]

Thanks, I corrected error in my custom helper, but when I call the helper from views as following: @HtmlHelperExt.CHGridTable(Model, new { tablename = "tblTest", defaultcolsort = "3" }) and got following error: Error CS0411 The type arguments for method 'HtmlHelperExt.CHGridTable(HtmlHelper, DataTable, object)' cannot be inferred from the usage. Try specifying the type arguments explicitly. The call on MVC5 works file, How can I use the custom helper on view of Core Web Application (MVC6): The custom helper code as following: public static IHtmlContent CHGridTable(this HtmlHelper htmlHelper, DataTable dt, object htmlAttributes = null) { var urlHelperFactory = (IUrlHelperFactory)htmlHelper.ViewContext.HttpContext.RequestServices.GetService(typeof(IUrlHelperFactory)); var url = urlHelperFactory.GetUrlHelper(htmlHelper.ViewContext); ...... return new HtmlString(tbBtnAdd.ToString() + tbGridTable.ToString() + script.ToString()); }

[Richard Deeming]

JimFeng wrote:

@HtmlHelperExt.CHGridTable(Model, new { tablename = "tblTest", defaultcolsort = "3" })

That should probably be:

@Html.CHGridTable(Model, new { tablename = "tblTest", defaultcolsort = "3" })

You need to call it as an extension method on the IHtmlHelper instance, not call the static method directly.

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"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

[JimFeng]

@Html.CHGridTable(......) works on MVC5 but not ASP.NET Core MVC.

[Richard Deeming]

Have you imported the tag helpers from your assembly? /Views/_ViewImports.cshtml:

@addTagHelper *, YourAssemblyNameHere

Managing Tag Helper scope | Tag Helpers in ASP.NET Core | Microsoft Docs[^]

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"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

[JimFeng]

I added @addTagHelper *, HtmlHelperExt in _ViewImports.cshtml file but still got error: Error: CS1061 'IHtmlHelper' does not contain a definition for 'CHDropdownMenu' and no accessible extension method 'CHDropdownMenu' accepting a first argument of type 'IHtmlHelper' could be found (are you missing a using directive or an assembly reference?) on the View page like this (the same as on MVC 5): @model System.Data.DataSet @using HtmlHelperExt; ...... @Html.CHDropdownMenu(Model, "mnuSample1", new { MenuOpenType = "Hover" }) ...... My Custom helper like this: namespace HtmlHelperExt { public static class HtmlHelperExt { public static IHtmlContent CHDropdownMenu(this HtmlHelper htmlHelper, DataSet ds, string divID, object htmlAttributes = null) { ...... return new HtmlString(tbDiv_Menu.ToString()); } } }

[Richard Deeming]

JimFeng wrote:

IHtmlHelper<dataset>' does not contain a definition for 'CHDropdownMenu'

CHDropdownMenu<tmodel>(this HtmlHelper<tmodel> htmlHelper,

You need to declare the helper method as an extension method against the IHtmlHelper interface, not the HtmlHelper class.

public static IHtmlContent CHDropdownMenu<TModel>(this IHtmlHelper<TModel> htmlHelper, ...

IHtmlHelper Interface (Microsoft.AspNetCore.Mvc.Rendering) | Microsoft Docs[^]

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"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

[JimFeng]

My assembly is a custom HtmlHelper NOT TagHelper.

[Richard Deeming]

Yes, of course. :doh: You'll want @using statements for your namespace, rather than @addTagHelper statements. Still in the _ViewImports.cshml file, though.

@using HtmlHelperExt

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"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

[JimFeng]

@using HtmlHelperExt is already in the _ViewImports.cshml, but got the same error.

[Richard Deeming]

Did you change the first parameter of the extension method, as I suggested yesterday?

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"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer

[JimFeng]

Thank you Rick, after I changed the parm type, and the helper works in my ASP.NET Core 2.1 MVC app.