Render ViewComponent as string

Rendering a View to a string is covered here. Turns out there’s a very similar approach to rendering a ViewComponent as a string. Here’s the code, thanks to this comment on the ASP.NET forums:

    public interface IViewRenderService
    {
        Task<string> RenderToStringAsync(string viewName, object model);
    }

    public class ViewRenderService : IViewRenderService
    {
        private readonly IRazorViewEngine _razorViewEngine;
        private readonly ITempDataProvider _tempDataProvider;
        private readonly IServiceProvider _serviceProvider;

        public ViewRenderService(IRazorViewEngine razorViewEngine,
            ITempDataProvider tempDataProvider,
            IServiceProvider serviceProvider)
        {
            _razorViewEngine = razorViewEngine;
            _tempDataProvider = tempDataProvider;
            _serviceProvider = serviceProvider;
        }

        public async Task<string> RenderToStringAsync(string viewName, object model)
        {
            var httpContext = new DefaultHttpContext { RequestServices = _serviceProvider };
            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());

            using var sw = new StringWriter();
            var viewResult = _razorViewEngine.FindView(actionContext, viewName, false);

            if (viewResult.View == null)
            {
                throw new ArgumentNullException($"{viewName} does not match any available view");
            }

            var viewDictionary = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary())
            {
                Model = model
            };

            var viewContext = new ViewContext(
                actionContext,
                viewResult.View,
                viewDictionary,
                new TempDataDictionary(actionContext.HttpContext, _tempDataProvider),
                sw,
                new HtmlHelperOptions()
            );

            await viewResult.View.RenderAsync(viewContext);
            return sw.ToString();
        }
    }

string result = await _viewRenderService.RenderToStringAsync("Shared/Components/Foo/Default", model);

// Don't forget to register the service so you can use constructor injection in your controller:

public void ConfigureServices(IServiceCollection services)
{
    /// ...
    services.AddScoped<IViewRenderService, ViewRenderService>();
}