T4MVC and R4MVC – Roslyn code generators for ASP.NET Core tag helpers

Dev Tips


I’ve always loved the T4 text generator within Visual Studio. If you are looking for T4 within Visual Studio 2017 you need to install the “Visual Studio extension development” option within the installer to access it. However, T4 development seems stalled/done and if you want to utilize some of it.

There’s a nice open source project called T4MVC that you can use with Visual Studio 2015 and ASP.NET MVC to create strongly typed helpers that eliminate the use of literal strings in many places. That means instead of:

@Html.ActionLink("Dinner Details", "Details", "Dinners", new { id = Model.DinnerID }, null)

T4MVC lets you write

@Html.ActionLink("Dinner Details", MVC.Dinners.Details(Model.DinnerID))

Fast forward to 2017 and that team is working on a new project called R4MVC…it’s a code generator that’s based on Roslyn, the .NET Compiler Platform (hence the R).

It also lets you update your @Html.ActionLinks to be strongly typed, but more importantly it lets you extend that to strongly typed taghelpers, so instead of:

<a asp-action="Details" asp-controller="Dinners" asp-route-id="@Model.DinnerID">Dinner Details</a>

you can write

<a mvc-action="MVC.Dinners.Details(Model.DinnerID)">Dinner Details</a>

It’s generating the URL for that <a> tag using the method and parameter.

Using an ASP.NET Core 1.1 app (2.0 is coming soon they say) I’ll add the NuGet packages R4Mvc.Tools and R4Mvc, making sure to “include prerelease.”

I’ll run “Generate-R4MVC” in the Package Manager Console.

Generate-R4MVC

There is a new R4Mvc.generated.cs file that gets created, and inside it is a whole bunch of classes based on the files on disk. For example I can type @Links.css, or @Links.lib and start getting intellisense for all my files on disk like JavaScript or CSS.

Links.css

When returning a view, rather than return View(“About”) I can do return View(Views.About):

return View(Views.About)

The R4MVC project also has Tag Helpers so their mvc-action attribute gives you strong typing like this:

<a mvc-action="MVC.Home.Index()">

This R4MVC project is just getting started, but I’m sure they’d appreciate your support! Head over to https://github.com/T4MVC/R4MVC/issues and learn about what they are planning and perhaps help out!

What do you think? Do you think there’s value in smarter or strongly-typed URL generation with ASP.NET?


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