How does AddRazorPages add support for MVC + views?

I want to use Razor Pages and "MVC with views" simultaneously.

So I used services.AddRazorPages() (which gives RazorPages and WebAPI) and then services.AddControllersWithViews() (which gives MVC and MVC+views).

That works.

But if I omit the latter, it also works. Why?

The source shows that AddRazorPages adds basic WebAPI support via services.AddMvcCore(). However I don't understand how/where mvc+views is added? I want to know whether this is expected behaviour or whether I've made a config mistake.

Actually, if you just use the AddMVCCore, it will not register the view service which will make your application not work with the view.

Like below error:

But the services.AddRazorPages will add the RazorViewEngine and it contains the View features which will make the MVC view works.

Source codes of the :

/// <summary>
/// Register services needed for Razor Pages.
/// </summary>
/// <param name="builder">The <see cref="IMvcCoreBuilder"/>.</param>
/// <param name="setupAction">The action to setup the <see cref="RazorPagesOptions"/>.</param>
/// <returns>The <see cref="IMvcCoreBuilder"/>.</returns>
public static IMvcCoreBuilder AddRazorPages(
    this IMvcCoreBuilder builder,
    Action<RazorPagesOptions> setupAction)
{
    ArgumentNullException.ThrowIfNull(builder);
    ArgumentNullException.ThrowIfNull(setupAction);

    builder.AddRazorViewEngine();

    AddRazorPagesServices(builder.Services);

    builder.Services.Configure(setupAction);

    return builder;
}

So if you use below codes inside the MVC application it will also work well.

builder.Services.AddMvcCore().AddRazorViewEngine();