How do i convert a partial view to String, so i can use it in signalr hub?

Question

I can't find a way to render a partial view inside a signalr hub, the real problem is that i don't know how i would convert the partial to a string.

I made a table partial that renders some data from my database, i want that data to be refreshed each 2 minutes, i using signalr hub for this purpose. But i need to pass my partial as a string to the hub, otherwise it won't work. Any ideas?

Hub Code (I was trying to use a function but it didnt work):

    public async Task<string> Teste()
    {
        var body = await _renderer.RenderPartialToStringAsync("../Areas/Admin/Pages/Partial/_Filas.cshtml", new principalModel());
        return body.ToString();
    }

Answer 1

You can use this class to render view to string :

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;

namespace RenderView.Models
{
    public class ViewRenderer
    {
        private readonly IRazorViewEngine _viewEngine;
        private readonly ITempDataProvider _tempDataProvider;
        private readonly IServiceProvider _serviceProvider;
        private readonly IHttpContextAccessor _httpContextAccessor;

        public ViewRenderer(
            IRazorViewEngine viewEngine,
            ITempDataProvider tempDataProvider,
            IServiceProvider serviceProvider,
            IHttpContextAccessor httpContextAccessor)
        {
            _viewEngine = viewEngine;
            _tempDataProvider = tempDataProvider;
            _serviceProvider = serviceProvider;
            _httpContextAccessor = httpContextAccessor;
        }


        public async Task<string> RenderViewToStringAsync<TModel>(string viewNameOrPath, TModel model)
        {
            var actionContext = GetActionContext();
            var view1 = _viewEngine.FindView(actionContext, viewNameOrPath, false);
            if (!view1.Success)
            {
                view1 = _viewEngine.GetView("~/", viewNameOrPath, false);
                if (!view1.Success)
                    throw new FileNotFoundException($"Couldn't find '{(object)viewNameOrPath}'");
            }

            var view2 = view1.View;
            await using var output = new StringWriter();
            var viewData = new ViewDataDictionary<TModel>((IModelMetadataProvider)new EmptyModelMetadataProvider(),
                new ModelStateDictionary())
            {
                Model = model
            };
            var context = new ViewContext(actionContext, view2, (ViewDataDictionary)viewData,
                (ITempDataDictionary)new TempDataDictionary(actionContext.HttpContext, this._tempDataProvider),
                (TextWriter)output, new HtmlHelperOptions());
            await view2.RenderAsync(context);
            var stringAsync = output.ToString();
            return stringAsync;
        }

        private ActionContext GetActionContext()
        {
            var httpContext = _httpContextAccessor?.HttpContext;
            if (httpContext != null)
                return new ActionContext(httpContext, httpContext.GetRouteData(), new ActionDescriptor());
            var defaultHttpContext = new DefaultHttpContext
            {
                RequestServices = this._serviceProvider
            };
            return new ActionContext((HttpContext)defaultHttpContext, new RouteData(), new ActionDescriptor());
        }
    }
}

And you should add this lines to startup:

builder.Services.AddMvcCore().AddRazorViewEngine();
builder.Services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();
builder.Services.AddScoped<ViewRenderer>();

Use ViewRenderer class as follows:

   public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;
        private readonly ViewRenderer _viewRenderer;

        public HomeController(ILogger<HomeController> logger, ViewRenderer viewRenderer)
        {
            _logger = logger;
            _viewRenderer = viewRenderer;
        }

        public async Task<IActionResult> Index()
        {
            var renderedView =await 
                _viewRenderer.RenderViewToStringAsync<MyViewModel>("_MyView", new MyViewModel() { Id = 1 });
            ViewData["RenderedView"]= renderedView;
            return View();

        }
        public class MyViewModel
        {
            public int Id { get; set; }
        }
    }