For ASP.NET Core 3 release version:

   services.AddControllersWithViews().AddRazorRuntimeCompilation();

https://docs.microsoft.com/en-us/aspnet/core/mvc/views/view-compilation?view=aspnetcore-3.0

It can also be enabled conditionally only for local development, quoted from the link:

Runtime compilation can be enabled such that it's only available for local development. Conditionally enabling in this manner ensures that the published output: Uses compiled views. Is smaller in size. Doesn't enable file watchers in production.

   public Startup(IConfiguration configuration, IWebHostEnvironment env)
    {
        Configuration = configuration;
        Env = env;
    }

    public IWebHostEnvironment Env { get; set; }
    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        IMvcBuilder builder = services.AddRazorPages();

#if DEBUG
            if (Env.IsDevelopment())
            {
                builder.AddRazorRuntimeCompilation();
            }
#endif
    }

OK it looks like it's not supported yet :(

Runtime compilation removed As a consequence of cleaning up the ASP.NET Core shared framework to not depend on Roslyn, support for runtime compilation of pages and views has also been removed in this preview release. Instead compilation of pages and views is performed at build time. In a future preview update we will provide a NuGet packages for optionally enabling runtime compilation support in an app.

You can read more about the issue here https://github.com/aspnet/Announcements/issues/343

Applications that require runtime compilation or re-compilation of Razor files should:

Add a reference to the Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation package. It'll be available as part of the 3.0.0-preview3 release.

Update the application's ConfigureServices to include a call to AddMvcRazorRuntimeCompilation:

To get runtime view compilation back in ASP.NET Core 3

Reference Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation Call services.AddMvc().AddRazorRuntimeCompilation() Remove Microsoft.VisualStudio.Web.CodeGeneration.Design if there's a version mismatch on the Microsoft.CodeAnalysis.Common package

Runtime compilation is enabled using the Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation package. To enable runtime compilation, apps must:

Install the Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation NuGet package. Update the project's Startup.ConfigureServices method to include a call to AddRazorRuntimeCompilation:

services
    .AddControllersWithViews()
    .AddRazorRuntimeCompilation();

https://docs.microsoft.com/en-us/aspnet/core/mvc/views/view-compilation?view=aspnetcore-3.0

To get runtime Razor Views Compilation back in ASP.NET Core 3.1:

Install the Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation NuGet package. Update the project's Startup.ConfigureServices method to include a call to AddRazorRuntimeCompilation. services.AddRazorPages().AddRazorRuntimeCompilation(); Razor file compilation in ASP.NET Core 3.1

Step 1: Install the below package from NuGet Package Manager for Solution.

Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation

https://i.stack.imgur.com/tDOmv.jpg

Step 2: Add the below code in ConfigureServices of Startup.cs file

services.AddControllersWithViews().AddRazorRuntimeCompilation();

https://i.stack.imgur.com/qmjv3.jpg

Save the page and then refresh the client browser.

If you are using Razor then add the code for services.AddRazorPages().AddRazorRuntimeCompilation();

In .NET Core 3.1, you need disable generation of the views.dll file.

Add the below code to your .csproj file (in the root of your project): netcoreapp3.1 ... true false false false Install the below package from the NuGet Package Manager for the Solution. Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation Add the below code to the ConfigureServices method of your Startup.cs file: services.AddMvc().AddRazorRuntimeCompilation(); Or services.AddControllersWithViews().AddRazorRuntimeCompilation(); Or services.AddRazorPages().AddRazorRuntimeCompilation();

After this, publish again and run it. It will work.

Simpliest way to configure Runtime Compilation for Local Development only is to update launch profiles in launchSettings.json. This method requires no code changes to configure a project which is running locally (it will not affect your production).

See the official documentation:

Install the Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation NuGet package. Modify the launch profile environmentVariables section in launchSettings.json: Verify ASPNETCORE_ENVIRONMENT is set to "Development". Set ASPNETCORE_HOSTINGSTARTUPASSEMBLIES to "Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation".

Example:

{
  "iisSettings": {
    "windowsAuthentication": false,
    "anonymousAuthentication": true,
    "iisExpress": {
      "applicationUrl": "http://localhost:57676",
      "sslPort": 44364
    }
  },
  "profiles": {
    "IIS Express": {
      "commandName": "IISExpress",
      "launchBrowser": true,
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development",
        "ASPNETCORE_HOSTINGSTARTUPASSEMBLIES": "Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation"
      }
    },
    "RazorPagesApp": {
      "commandName": "Project",
      "launchBrowser": true,
      "applicationUrl": "https://localhost:5001;http://localhost:5000",
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development",
        "ASPNETCORE_HOSTINGSTARTUPASSEMBLIES": "Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation"
      }
    }
  }
}

Just an added note -- you may want to only conditionally enable this runtime compilation, so that the published output:

Uses compiled views.

Is smaller in size.

Doesn't enable file watchers in production.

Conditionally enable runtime compilation