Render a Razor Page to string

user_2719183 0
Viewed 11103

Problem:

I need to render a Razor Page partial to a string.

Why I want this:

I want to create a controller action that responds with JSON containing a partial view and other optional parameters.

Attempts:

I am familiar with the following example that renders a View to a string: https://github.com/aspnet/Entropy/blob/dev/samples/Mvc.RenderViewToString/RazorViewToStringRenderer.cs

However, it is not compatible with Pages, as it only searches in the Views directory, so even if I give it an absolute path to the partial it tries to locate my _Layout.cshtml (which it shouldn't even do!) and fails to find it.

I have tried to modify it so it renders pages, but I end up getting a NullReferenceException for ViewData in my partial when attempting to render it. I suspect it has to do with NullView, but I have no idea what to put there instead (the constructor for RazorView requires many objects that I don't know how to get correctly).

The code:

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0: https://www.apache.org/licenses/LICENSE-2.0
// Modified by OronDF343: Uses pages instead of views.

using System;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
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.Mvc.ViewFeatures.Internal;
using Microsoft.AspNetCore.Routing;

namespace TestAspNetCore.Services
{
    public class RazorPageToStringRenderer
    {
        private readonly IRazorViewEngine _viewEngine;
        private readonly ITempDataProvider _tempDataProvider;
        private readonly IServiceProvider _serviceProvider;

        public RazorPageToStringRenderer(
            IRazorViewEngine viewEngine,
            ITempDataProvider tempDataProvider,
            IServiceProvider serviceProvider)
        {
            _viewEngine = viewEngine;
            _tempDataProvider = tempDataProvider;
            _serviceProvider = serviceProvider;
        }

        public async Task<string> RenderPageToStringAsync<TModel>(string viewName, TModel model)
        {
            var actionContext = GetActionContext();
            var page = FindPage(actionContext, viewName);

            using (var output = new StringWriter())
            {
                var viewContext = new ViewContext(actionContext,
                                                  new NullView(),
                                                  new ViewDataDictionary<TModel>(new EmptyModelMetadataProvider(),
                                                                                 new ModelStateDictionary())
                                                  {
                                                      Model = model
                                                  },
                                                  new TempDataDictionary(actionContext.HttpContext,
                                                                         _tempDataProvider),
                                                  output,
                                                  new HtmlHelperOptions());

                page.ViewContext = viewContext;
                await page.ExecuteAsync();

                return output.ToString();
            }
        }

        private IRazorPage FindPage(ActionContext actionContext, string pageName)
        {
            var getPageResult = _viewEngine.GetPage(executingFilePath: null, pagePath: pageName);
            if (getPageResult.Page != null)
            {
                return getPageResult.Page;
            }

            var findPageResult = _viewEngine.FindPage(actionContext, pageName);
            if (findPageResult.Page != null)
            {
                return findPageResult.Page;
            }

            var searchedLocations = getPageResult.SearchedLocations.Concat(findPageResult.SearchedLocations);
            var errorMessage = string.Join(
                Environment.NewLine,
                new[] { $"Unable to find page '{pageName}'. The following locations were searched:" }.Concat(searchedLocations));

            throw new InvalidOperationException(errorMessage);
        }

        private ActionContext GetActionContext()
        {
            var httpContext = new DefaultHttpContext { RequestServices = _serviceProvider };
            return new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
        }
    }
}
asp.net-core-2.0 razor-pages asp.net-core razor c#
4 Answers

If like me you don't get GetRouteData() from _httpContext.HttpContext and _actionContext is null, you can create an extension:

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewEngines;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Text.Encodings.Web;
using System.Threading.Tasks;

namespace Utils
{
    public static class PageExtensions
    {
        public static async Task<string> RenderViewAsync(this PageModel pageModel, string pageName)
        {
            var actionContext = new ActionContext(
                pageModel.HttpContext,
                pageModel.RouteData,
                pageModel.PageContext.ActionDescriptor
            );

            using (var sw = new StringWriter())
            {
                IRazorViewEngine _razorViewEngine = pageModel.HttpContext.RequestServices.GetService(typeof(IRazorViewEngine)) as IRazorViewEngine;
                IRazorPageActivator _activator = pageModel.HttpContext.RequestServices.GetService(typeof(IRazorPageActivator)) as IRazorPageActivator;

                var result = _razorViewEngine.FindPage(actionContext, pageName);

                if (result.Page == null)
                {
                    throw new ArgumentNullException($"The page {pageName} cannot be found.");
                }

                var page = result.Page;

                var view = new RazorView(_razorViewEngine,
                    _activator,
                    new List<IRazorPage>(),
                    page,
                    HtmlEncoder.Default,
                    new DiagnosticListener("ViewRenderService"));


                var viewContext = new ViewContext(
                    actionContext,
                    view,
                    pageModel.ViewData,
                    pageModel.TempData,
                    sw,
                    new HtmlHelperOptions()
                );


                var pageNormal = ((Page)result.Page);

                pageNormal.PageContext = pageModel.PageContext;

                pageNormal.ViewContext = viewContext;


                _activator.Activate(pageNormal, viewContext);

                await page.ExecuteAsync();

                return sw.ToString();
            }
        }
    }
}

Note: this code only render the page being called and omit the layout.

You just have to call it from your PageModel like this:

var s = this.RenderViewAsync("sendEmail").Result;

"sendEmail" is the name of your PageModel view and the path is /Pages/sendEmail.cshtml

user_35026260

I had the same problem.

I looked into the RazorViewEngine source code and found out that the page is searched using the "page" route data:

var routeData = new RouteData();
routeData.Values.Add("page", "/Folder/MyPage");

It's working for me with the full path "/Folder/MyPage" in the routeData, and the page name "MyPage" in the GetPage call.

user_79196120

Here is the route I have gone down. Very simple and works a treat...

using System;
using System.IO;
using System.Net;

namespace gMIS.Rendering
{
    public static class RazorPage
    {
        public static string RenderToString(string url)
        {
            try
            {
                //Grab page
                WebRequest request = WebRequest.Create(url);
                WebResponse response = request.GetResponse();
                Stream data = response.GetResponseStream();
                string html = String.Empty;
                using (StreamReader sr = new StreamReader(data))
                {
                    html = sr.ReadToEnd();
                }
                return html;
            }
            catch (Exception err)
            {
                return {Handle as you see fit};
            }
        }
    }
}

Called as such....

var msg = RazorPage.RenderToString(url);

Example:

var pathToRazorPageFolder = request.PathToRazorPageFolder();

var msg = RazorPage.RenderToString($"{pathToRazorPageFolder}/Task_Summary?userGuid={userGuid}&taskId={task.Task_ID}&includelink=true&linkuserGuid={linkUserGuid}");

Above example uses this extension I created to help get the base path of my app.

namespace Microsoft.AspNetCore.Http
{
    public static class RequestExtension
    {
        public static string PathToRazorPageFolder(this HttpRequest request)
        {
            if (request != null) {
                var requestPath = request.Path.ToString();
                var returnPathToFolder = request.Scheme + "://" + request.Host + requestPath.Substring(0, requestPath.LastIndexOf("/")); ;
                return returnPathToFolder;
            } else
            {
                return "HttpRequest was null";
            }
        }
    }
}

I know that this doesn't use Dependency Injection, but man it's simple. And it just works. And works with any page no matter how it is hosted. Be that page be within or even outside your application.

user_106121230
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