无法解析类型 Microsoft.AspNetCore.Mvc.Razor.IRazorViewEngine 的服务

Question

在我的 core 2.2 项目中，我有返回 Razor View 作为字符串的标准服务（我需要它在我用 WPF 编写的客户端中生成 pdf）：

public class RaportService : IRaportService
    {
        private readonly IProjectRepository projectRepository;
        private readonly IRazorViewEngine razorViewEngine;
        private readonly ITempDataProvider tempDataProvider;
        private readonly IServiceProvider serviceProvider;

        public RaportService(
            IProjectRepository projectRepository,
            IRazorViewEngine razorViewEngine,
            ITempDataProvider tempDataProvider,
            IServiceProvider serviceProvider)
        {
            this.projectRepository = projectRepository;
            this.razorViewEngine = razorViewEngine;
            this.tempDataProvider = tempDataProvider;
            this.serviceProvider = serviceProvider;
        }

        public async Task<string> GenerateProjectRaport(int projectId)
        {
            var project = await this.projectRepository.GetProjectWithTasksAsync(projectId)
                ?? throw new EntityNotFoundException();

            var httpContext = new DefaultHttpContext { RequestServices = this.serviceProvider };
            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());

            using (var stringWriter = new StringWriter())
            {
                string viewPath = "~/wwwroot/RaportTemplate.cshtml";

                var viewResult = this.razorViewEngine.GetView(viewPath, viewPath, false);

                var viewDictionary = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary())
                {
                    Model = new RaportViewModel
                    {
                        Project = project,
                        ProjectTasks = project.Tasks.ToList(),
                        ProjectEndedTasks = project.EndedTasks.ToList(),
                    }
                };

                var viewContext = new ViewContext(
                    actionContext,
                    viewResult.View,
                    viewDictionary,
                    new TempDataDictionary(actionContext.HttpContext, this.tempDataProvider),
                    stringWriter,
                    new HtmlHelperOptions());

                await viewResult.View.RenderAsync(viewContext);
                return stringWriter.ToString();
            }
        }
    }

在 Core 2.2 中一切正常。当我将项目更新为 Core 3.0 时，出现此错误：

{
    "stackTrace":"   at MediatR.Internal.RequestHandlerBase.GetHandler[THandler](ServiceFactory factory)\r\n   
at MediatR.Internal.RequestHandlerWrapperImpl`2.<>c__DisplayClass0_0.<Handle>g__Handler|0()\r\n   at MediatR.Pipeline.RequestPostProcessorBehavior`2.Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate`1 next)\r\n   
at MediatR.Pipeline.RequestPreProcessorBehavior`2.Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate`1 next)\r\n  
 at TaskManager.Api.Controllers.RaportController.GetProjectRaport(Int32 projectId) in C:\Users\Michał\Source\Repos\michasacuer\TaskManager\Src\Web\TaskManager.Api\Controllers\RaportController.cs:line 12\r\n   at lambda_method(Closure , Object )\r\n   
at Microsoft.Extensions.Internal.ObjectMethodExecutorAwaitable.Awaiter.GetResult()\r\n   
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)\r\n   
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)\r\n   
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)\r\n  
 at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)\r\n   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)\r\n   
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n  
 at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextExceptionFilterAsync>g__Awaited|25_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)",
    "message":"Error constructing handler for request of type MediatR.IRequestHandler`2[TaskManager.Application.Raport.Queries.GetProjectRaport.GetProjectRaportQuery,System.String]. Register your handlers with the container. See the samples in GitHub for examples."}

即使我在 Startup 中注册 IRazorViewEngine 接口和 class 它仍然抛出，他需要调用 IRazorPageFactoryProvider 的东西但我不知道，什么是它的一个实现。

那么如何让 Razor View Engine 与 .NET Core 3.0 一起工作？

Answer 1

我找到了解决方案。当您想在 .Net Core 3.0 中访问 RazorViewEngine 时（尤其是在 Web Api 中）将这两行添加到您的 Startup.cs:

services.AddControllersWithViews();
services.AddRazorPages();

Answer 2

解决方法是添加所需的服务。下面的代码完成了这项工作。在 Startup.cs 中，诀窍是从 AddMvcCore() 或 AddMvc 中获取 builder，然后调用 AddRazorViewEngine

var builder = services.AddMvcCore();
builder.AddRazorViewEngine();

Answer 3

如果您只想访问 RazorViewEngine，您可以使用 AddMvcCore().AddRazorViewEngine()。现在只要使用 DI

就可以随心所欲地访问它

public void ConfigureServices(IServiceCollection services) {
    ...
    services.AddMvcCore().AddRazorViewEngine();
}