voidkitty/VoidCat/Services/ViewRenderer.cs

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;

namespace VoidCat.Services;

public class RazorPartialToStringRenderer
{
    private readonly IRazorViewEngine _viewEngine;
    private readonly ITempDataProvider _tempDataProvider;
    private readonly IServiceProvider _serviceProvider;

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

    public async Task<string> RenderPartialToStringAsync<TModel>(string partialName, TModel model)
    {
        var actionContext = GetActionContext();
        var partial = FindView(actionContext, partialName);
        await using var output = new StringWriter();
        var viewContext = new ViewContext(
            actionContext,
            partial,
            new ViewDataDictionary<TModel>(
                metadataProvider: new EmptyModelMetadataProvider(),
                modelState: new ModelStateDictionary())
            {
                Model = model
            },
            new TempDataDictionary(
                actionContext.HttpContext,
                _tempDataProvider),
            output,
            new HtmlHelperOptions()
        );
        await partial.RenderAsync(viewContext);
        return output.ToString();
    }

    private IView FindView(ActionContext actionContext, string partialName)
    {
        var getPartialResult = _viewEngine.GetView(null, partialName, false);
        if (getPartialResult.Success)
        {
            return getPartialResult.View;
        }

        var findPartialResult = _viewEngine.FindView(actionContext, partialName, false);
        if (findPartialResult.Success)
        {
            return findPartialResult.View;
        }

        var searchedLocations = getPartialResult.SearchedLocations.Concat(findPartialResult.SearchedLocations);
        var errorMessage = string.Join(
            Environment.NewLine,
            new[] {$"Unable to find partial '{partialName}'. 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());
    }
}