Renderizar una View a String

Fuentes

• https://ppolyzos.com/2016/09/09/asp-net-core-render-view-to-string/

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Para envió de emails.

Crear un Servicio

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Routing;
using System;
using System.IO;
using System.Threading.Tasks;

namespace Prueba.Services
{
    public interface IViewRenderService
    {
        Task<string> RederToStringAsync<TModel>(string viewName, TModel model);
    }

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

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

        public async Task<string> RederToStringAsync<TModel>(string viewName, TModel 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 is null)
                {
                    throw new ArgumentNullException($"{viewName} does not math 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();
            }
        }
    }
}

Registrar el Servicio

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