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Share reusable UI components through a Razor class library

One ASP.NET Core feature that I really like and most people are not aware of it existence are Razor Class libraries(RCL). With RCL you can package Razor views, pages, Razor components and view components and reuse them in different applications.

I blogged about RCL before and although I really like the feature I got feedback from my development teams that the behavior was not consistent and they sometimes couldn’t get it working. I never had time to really investigate the root cause until now.

So this blog post is here to explain my findings.

The development environment

First of all it is important to understand that the behavior of RCL is different in Development compared to other environments. When running the app that uses the RCL from build output (dotnet run), static web assets are enabled that allow ASP.NET Core to load static web assets from locations outside the wwwroot. This is required because ASP.NET Core will load the assets directly from the RCL NuGet location. 

By default this is only enabled in the Development environment. To support assets in other environments when running from build output, call UseStaticWebAssets on the host builder in Program.cs:

So that explains some of the issues that people encountered. This only works in Development so if you created and used a different environment during development the assets are not loaded.

dotnet publish

The second important thing to remember is that the behavior is completely different when you publish your application. When you run dotnet publish, the static content from the RCL is copied over to the wwwroot folder:

Because the files are served as static content, the Static files middleware should be enabled as well:

Hope that helps!

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