Changes to *.cshtml files not get autodetected on dotnet core 3.0 - razor

Question

Steps to reproduce a problem:
Download and install dotnet core 3.0
Create a new project: dotnet new webapp -n MyApp
Run app dotnet run
Navigate to http://localhost:5000/Privacy
Edit Privacy page MyApp\Pages\Privacy.cshtml
Refresh
The changes do not get picked up by the toolkit and old page is rendered.
Same flow for dotnet core 2.2 (freshly installed) results in an updated page.
Is there a flag, which needs to be set somewhere within config to get autodetect working for 3.0 or is this a bug?

Answer 1

Use the dotnet CLI command to watch run your project:
dotnet watch run
Optionally you can watch run without hot reload enabled:
dotnet watch run --no-hot-reload
Add this instruction to the project file [ProjectName].csproj:
<ItemGroup>
<!-- extends watching group to include *.cshtml and *.razor files -->
<Watch Include="**\*.cshtml;*.razor;*.js;*.css" Exclude="**\obj\**\*;bin\**\*" />
</ItemGroup>
For further information see Microsoft DotNet 5.0 Documentation.

Answer 2

While searching the root cause of that issue i came accross with that SO question. To resolve that issue you need to add Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation NuGet package to your project and modify your Startup.cs like below.
Inside ConfigureServices method of Startup.cs
For ASP.NET Core MVC:
IMvcBuilder mvc = services.AddControllersWithViews();
mvc.AddRazorRuntimeCompilation();
For ASP.NET Core Razor Pages:
IMvcBuilder mvc = services.AddRazorPages();
mvc.AddRazorRuntimeCompilation();
PS: Do not forget to use this feature 'dotnet-watch' for development environment only since it does not make sense for production environment for most cases.
Source: https://learn.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.0&tabs=visual-studio
2021 UPDATE (Better Solution): You do not need to execute AddRazorRuntimeCompilation method in Startup.cs. You can keep this feature running by adding a value to projects debug configuration.
Please add new Environment variable to Project Properties > Debug > Environment variables
Name: ASPNETCORE_HOSTINGSTARTUPASSEMBLIES
Value: Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation

Answer 3

I'm not entirely sure this is the same issue, but ASP.NET Core 2.2 introduced an In Process IIS hosting model. This provides a lot of performance benefits in a production environment, but basically negates one of ASP.NET Core's most useful development features: automatic updates. If you're using the In Process model in development, you'll need to build after code changes, just like with older ASP.NET MVC sites. You can switch the hosting model back to the Out of Process model (the old way) either by going to your project properties or editing your csproj. In properties, there's a dropdown now on the Debug tab, which corresponds to the <AspNetCoreHostingModel> tag in the csproj.
UPDATE
For what it's worth, I've actually seen this behavior to be somewhat random actually. Some changes for me seem to kick off an automatic build like they used to, while other changes don't show up unless I manually build. There doesn't seem to be a lot of rhyme or reason to which changes required what either. It's possible that the tooling for this isn't quite there yet, and a future update to Visual Studio may make the In Process model behave consistently like the Out of Process model did with code changes in development. All I know is that switching to Out of Process definitely resolves all issues with this, so it's related to the In Process model in some way.