Render a Razor View containing a URL to a string in ASP.NET Core - asp.net-core-mvc

Question

I have an Emailer class I am using via Dependency Injection to send emails which gets the contents of a View to send in an email. The process I have works great UNLESS the view contains a call to the underlying URL helper, such as using an A tag like this:
<a asp-controller="Project" asp-action="List">Open</a>
Here is the code I am using to render a view into a string:
private string renderViewAsString<TModel>(string folder, string viewName, TModel model)
{
var httpContext = new DefaultHttpContext { RequestServices = _serviceProvider };
var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
var viewEngineResult = _viewEngine.FindView(actionContext, folder + "/" + viewName, false);
var view = viewEngineResult.View;
var viewData = new ViewDataDictionary<TModel>(new EmptyModelMetadataProvider(), new ModelStateDictionary());
viewData.Model = model;
var tempData = new TempDataDictionary(httpContext, _tempDataProvider);
using (var output = new StringWriter())
{
var viewContext = new ViewContext(actionContext, view, viewData, tempData, output, new HtmlHelperOptions());
var task = view.RenderAsync(viewContext);
task.Wait();
return output.ToString();
}
}
_serviceProvider is of type IServiceProvider and _viewEngine is of type IRazorViewEngine which are both injected in the constructor.
If it references the URL helper it produces this exception at the task.Wait() line:
Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
with this as the call stack:
at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
at System.Collections.Generic.List`1.get_Item(Int32 index)
at Microsoft.AspNetCore.Mvc.Routing.UrlHelper.get_Router()
at Microsoft.AspNetCore.Mvc.Routing.UrlHelper.GetVirtualPathData(String routeName, RouteValueDictionary values)
at Microsoft.AspNetCore.Mvc.Routing.UrlHelper.Action(UrlActionContext actionContext)
at Microsoft.AspNetCore.Mvc.UrlHelperExtensions.Action(IUrlHelper helper, String action, String controller, Object values, String protocol, String host, String fragment)
at Microsoft.AspNetCore.Mvc.ViewFeatures.DefaultHtmlGenerator.GenerateActionLink(ViewContext viewContext, String linkText, String actionName, String controllerName, String protocol, String hostname, String fragment, Object routeValues, Object htmlAttributes)
at Microsoft.AspNetCore.Mvc.TagHelpers.AnchorTagHelper.Process(TagHelperContext context, TagHelperOutput output)
at Microsoft.AspNetCore.Razor.TagHelpers.TagHelper.ProcessAsync(TagHelperContext context, TagHelperOutput output)
at Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner.<RunAsync>d__0.MoveNext()
How do I get around this without having to resort to hard-coding the A element or email contents?

Answer 1

I was able to get it to work. The call stack mentioned not finding a router, so it was a matter of providing it:
First I added this as a DI object in the constructor parameters:
IHttpContextAccessor accessor
And this in the constructor:
_context = accessor.HttpContext;
Then I changed the function to this:
private string renderViewAsString<TModel>(string folder, string viewName, TModel model)
{
var actionContext = new ActionContext(_context, new RouteData(), new ActionDescriptor());
var viewEngineResult = _viewEngine.FindView(actionContext, folder + "/" + viewName, false);
var view = viewEngineResult.View;
var viewData = new ViewDataDictionary<TModel>(new EmptyModelMetadataProvider(), new ModelStateDictionary());
viewData.Model = model;
var tempData = new TempDataDictionary(_context, _tempDataProvider);
using (var output = new StringWriter())
{
var viewContext = new ViewContext(actionContext, view, viewData, tempData, output, new HtmlHelperOptions());
viewContext.RouteData = _context.GetRouteData(); //set route data here
var task = view.RenderAsync(viewContext);
task.Wait();
return output.ToString();
}
}

Answer 2

This is the one I use in ASP.NET Core 2.0
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
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.ViewEngines;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Routing;
namespace Website
{
public class RazorViewToStringRenderer
{
private readonly IHttpContextAccessor accessor;
private readonly IRazorViewEngine viewEngine;
private readonly IServiceProvider serviceProvider;
private readonly ITempDataProvider tempDataProvider;
public RazorViewToStringRenderer(
IHttpContextAccessor accessor,
IRazorViewEngine viewEngine,
IServiceProvider serviceProvider,
ITempDataProvider tempDataProvider)
{
this.accessor = accessor;
this.viewEngine = viewEngine;
this.serviceProvider = serviceProvider;
this.tempDataProvider = tempDataProvider;
}
public string RenderViewToString<TModel>(string viewLocation, TModel model)
{
HttpContext httpContext = accessor.HttpContext;
httpContext.RequestServices = serviceProvider;
ActionContext actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
IView view = FindView(actionContext, viewLocation);
using (StringWriter stringWriter = new StringWriter())
{
ViewDataDictionary<TModel> viewDataDictionary = new ViewDataDictionary<TModel>(
new EmptyModelMetadataProvider(),
new ModelStateDictionary());
viewDataDictionary.Model = model;
TempDataDictionary tempDataDictionary = new TempDataDictionary(
actionContext.HttpContext,
tempDataProvider);
HtmlHelperOptions htmlHelperOptions = new HtmlHelperOptions();
ViewContext viewContext = new ViewContext(
actionContext,
view,
viewDataDictionary,
tempDataDictionary,
stringWriter,
htmlHelperOptions);
viewContext.RouteData = accessor.HttpContext.GetRouteData();
view.RenderAsync(viewContext).Wait();
return stringWriter.ToString();
}
}
private IView FindView(ActionContext actionContext, string viewLocation)
{
ViewEngineResult getViewResult = viewEngine.GetView(null, viewLocation, true);
if (getViewResult.Success)
{
return getViewResult.View;
}
ViewEngineResult findViewResult = viewEngine.FindView(actionContext, viewLocation, true);
if (findViewResult.Success)
{
return findViewResult.View;
}
IEnumerable<string> searchedLocations = getViewResult.SearchedLocations.Concat(findViewResult.SearchedLocations);
string message = string.Join(
Environment.NewLine,
new[] { $"Unable to find view '{viewLocation}'. The following locations were searched:" }.Concat(searchedLocations)); ;
throw new Exception(message);
}
}
}
Remember in Startup.cs -> public void ConfigureServices(IServiceCollection serviceCollection) to add this
serviceCollection.AddSingleton<RazorViewToStringRenderer>();

Answer 3

I have no direct answer to this, because i have the exact same problem. But i made a Github issue yesterday. https://github.com/aspnet/Entropy/issues/170
Edit: The solution of Rono works for me

Answer 4

I had the same error, but I couldn't use Rono's solution because it required a real HttpContext, which I did not have in my command-line application. I managed to fix it by adding a RouteCollection to my ActionContext:
private ActionContext GetActionContext()
{
var httpContext = new DefaultHttpContext { RequestServices = serviceProvider };
var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
MapRoutes(actionContext);
return actionContext;
}
private void MapRoutes(ActionContext actionContext)
{
var routes = new RouteBuilder(new ApplicationBuilder(serviceProvider))
{
DefaultHandler = new DefaultHandler()
};
routes.MapRoute(
name: "default",
template: "{controller=Home}/{action=Index}/{id?}"
);
actionContext.RouteData.Routers.Add(routes.Build());
}
Full source code with an example project on github: https://github.com/waf/RazorToStringExample/blob/master/RazorToStringExample/Services/RazorViewToStringRenderer.cs