Renders Blazor Components and Razor Views into HTML

HtmlRenderer.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.Encodings.Web;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Components;
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.TagHelpers;
using Microsoft.AspNetCore.Mvc.ViewEngines;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;
using Microsoft.AspNetCore.Routing;

namespace HtmlRendering;

public interface IHtmlRenderer
{
	Task<string> RenderBlazorComponentAsync<TComponent>(Dictionary<string, object> parameters) where TComponent : IComponent;
	Task<string> RenderRazorViewToStringAsync<TModel>(string viewName, TModel model);
}
/// <summary>
/// Html rendering code mashed together from various stackoverflow answers and blog posts.
/// </summary>
public class HtmlRenderer : IHtmlRenderer
{
	private readonly IHttpContextAccessor httpContextAccessor;
	private readonly IRazorViewEngine razorViewEngine;
	private readonly ITempDataProvider tempDataProvider;

	public HtmlRenderer(
		IHttpContextAccessor httpContextAccessor,
		IRazorViewEngine razorViewEngine,
		ITempDataProvider tempDataProvider)
	{
		this.httpContextAccessor = httpContextAccessor;
		this.razorViewEngine = razorViewEngine;
		this.tempDataProvider = tempDataProvider;
	}

	/// <summary>
	/// Renders a blazor component as html.
	/// </summary>
	/// <typeparam name="TComponent">The type of the blazor component.</typeparam>
	/// <param name="parameters">Parameters to pass to the blazor component.</param>
	/// <returns>Task with string of html from rendered component.</returns>
	public async Task<string> RenderBlazorComponentAsync<TComponent>(Dictionary<string, object> parameters) where TComponent : IComponent
	{
		var componentTagHelper = new ComponentTagHelper
		{
			ComponentType = typeof(TComponent),
			RenderMode = RenderMode.Static,
			Parameters = parameters,
			ViewContext = new ViewContext { HttpContext = httpContextAccessor.HttpContext },
		};

		//uniqueid and tagName are arbitrary

		var tagHelperContext = new TagHelperContext(
			new TagHelperAttributeList(),
			new Dictionary<object, object>(),
			"uniqueid");

		var tagHelperOutput = new TagHelperOutput(
			"tagName",
			new TagHelperAttributeList(),
			(useCachedResult, encoder) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));

		await componentTagHelper.ProcessAsync(tagHelperContext, tagHelperOutput);

		using var stringWriter = new StringWriter();

		tagHelperOutput.Content.WriteTo(stringWriter, HtmlEncoder.Default);

		return stringWriter.ToString();
	}

	/// <summary>
    /// Renders a razor view as html.
    /// </summary>
    /// <typeparam name="TModel">The type of the view model.</typeparam>
    /// <param name="viewName">The name of the view. ex. ~/Views/MyView.cshtml</param>
    /// <param name="model">The view model.</param>
    /// <returns>Task with string of html from rendered view.</returns>
    /// <exception cref="InvalidOperationException"></exception>
	public async Task<string> RenderRazorViewToStringAsync<TModel>(string viewName, TModel model)
	{
		var actionContext = new ActionContext(httpContextAccessor.HttpContext, httpContextAccessor.HttpContext.GetRouteData(), new ActionDescriptor());
		var view = FindView(actionContext, viewName);

		using var output = new StringWriter();

		var viewContext = new ViewContext(
			actionContext,
			view,
			new ViewDataDictionary<TModel>(
				metadataProvider: new EmptyModelMetadataProvider(),
				modelState: new ModelStateDictionary())
			{
				Model = model
			},
			new TempDataDictionary(
				actionContext.HttpContext,
				tempDataProvider),
			output,
			new HtmlHelperOptions());

		await view.RenderAsync(viewContext);

		return output.ToString();
		IView FindView(ActionContext actionContext, string viewName)
		{
			var getViewResult = razorViewEngine.GetView(executingFilePath: null, viewPath: viewName, isMainPage: true);
			if (getViewResult.Success)
			{
				return getViewResult.View;
			}

			var findViewResult = razorViewEngine.FindView(actionContext, viewName, isMainPage: true);
			if (findViewResult.Success)
			{
				return findViewResult.View;
			}

			var searchedLocations = getViewResult.SearchedLocations.Concat(findViewResult.SearchedLocations);
			var errorMessage = string.Join(
				Environment.NewLine,
				new[] { $"Unable to find view '{viewName}'. The following locations were searched:" }.Concat(searchedLocations));
			throw new InvalidOperationException(errorMessage);
		}
	}
}