在迁移到 .Net Core 3.1 时，.Net Core 2.2 中使用的 Services.AddMvc() 和 SuperJsonOutputFormatter 的替代方法是什么

Question

我正在迁移一个 .Net Core 2.2 web API 应用程序，它只有 API 控制器，没有视图。我使用 SuperJsonOutputFormatter 在我的项目中设置了自定义 API 响应。现在，我正在使用 NewtonsoftJsonOutputFormatter 为 API 创建自定义响应。但根据微软文档，services.AddMvc() 在 .Net Core 3.1 中已过时。那么，如何调用 startup.cs 中的 customformatter。我正在使用下面的代码

services.AddControllers().AddNewtonsoftJson(options =>
{
    options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
    options.SerializerSettings.Formatting = Formatting.Indented;
});
services.AddScoped<SuperJsonOutputFormatterFilter>();
services.AddMvc(opts =>
{
    opts.EnableEndpointRouting = false;
    var oldFormatter = opts.OutputFormatters.OfType<CustomOutputFormatter>().Single();
    opts.OutputFormatters.Remove(oldFormatter);
    var replacementJsonOutputFormatter =
       new CustomOutputFormatter(oldFormatter.serializerSettings, ArrayPool<char>.Shared);
    opts.OutputFormatters.Add(replacementJsonOutputFormatter);
}).SetCompatibilityVersion(CompatibilityVersion.Version_3_0);

配置服务如下

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
   if (env.IsDevelopment())
   {
      app.UseDeveloperExceptionPage();
   }
   else
   {
      app.UseHsts();
   }
   app.UseRouting();
   app.UseExceptionHandler("/Error");
   app.UseAuthentication();
   app.UseStaticFiles();
   app.UseHttpsRedirection();
   app.UseMvc();
}

上面的代码给出了一个运行时错误，无法构建某些服务，验证服务描述符时出错。如何在不使用 Services.AppMvc()

的情况下调用 customformatter

我的Error_Helper如下

错误描述Class

 public class ErrorDescription
    {
        public ErrorDescription(HttpStatusCode statusCode)
        {
            this.Code = (int)statusCode;
            this.Description = GetDescription((int)statusCode);
        }

        string GetDescription(int statusCode)
        {
            return statusCode switch
            {
                404 => "Employee ID not found",
                500 => "Internal server error",
                400 => "Device token already registered",
                406 => "No data found in table",
                _ => "",
            };
        }


        [JsonProperty("errorCode")]
        public int Code { get; set; }
        [JsonProperty("errorDescription")]
        public string Description { get; set; }
    }

格式过滤器Class

 public class CustomJsonOutputFormatterFilter : IAsyncActionFilter
    {
        private readonly CustomOutputFormatter _formatter;
        // inject SuperJsonOutputFormatter service
        public CustomJsonOutputFormatterFilter(CustomOutputFormatter formatter)
        {
            this._formatter = formatter;
        }
        // a helper method that provides an ObjectResult wrapper over the raw object
        private ObjectResult WrapObjectResult(ActionExecutedContext context, object obj)
        {
            var wrapper = new ObjectResult(obj);
            wrapper.Formatters.Add(this._formatter);
            context.Result = wrapper;
            return wrapper;
        }

        public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
        {
            ActionExecutedContext resultContext = await next();
            // in case we get a 500
            if (resultContext.Exception != null && !resultContext.ExceptionHandled)
            {
                var ewrapper = this.WrapObjectResult(resultContext, new { });
                ewrapper.StatusCode = (int)HttpStatusCode.InternalServerError;
                resultContext.ExceptionHandled = true;
                return;
            }
            else
            {
                switch (resultContext.Result)
                {
                    case BadRequestObjectResult b:      // 400 with an object
                        var bwrapper = this.WrapObjectResult(resultContext, b.Value);
                        bwrapper.StatusCode = b.StatusCode;
                        break;
                    case NotFoundObjectResult n:        // 404 with an object
                        var nwrapper = this.WrapObjectResult(resultContext, n.Value);
                        nwrapper.StatusCode = n.StatusCode;
                        break;
                    case ObjectResult o:                // plain object
                        this.WrapObjectResult(resultContext, o.Value);
                        break;
                    case JsonResult j:                  // plain json
                        this.WrapObjectResult(resultContext, j.Value);
                        break;
                    case StatusCodeResult s:             // other statusCodeResult(including NotFound,NoContent,...), you might want to custom this case 
                        var swrapper = this.WrapObjectResult(resultContext, new { result="" });
                        swrapper.StatusCode = s.StatusCode;
                        break;
                }
            }
        }

    }

Custom Outputformatter Class，这个 class 调用 customformatterfilter

 public class CustomOutputFormatter : NewtonsoftJsonOutputFormatter
    {
        public CustomOutputFormatter(JsonSerializerSettings serializerSettings,
            ArrayPool<char> charPool) : base (serializerSettings, charPool)
        {
        }

        public JsonSerializerSettings serializerSettings { get; private set; }



        public override async Task WriteResponseBodyAsync(
            OutputFormatterWriteContext context,
            Encoding selectedEncoding)
        {

            if (context == null)
                throw new ArgumentNullException(nameof(context));
            if (selectedEncoding == null)
            if (selectedEncoding == null)
                throw new ArgumentNullException(nameof(selectedEncoding));
            using TextWriter writer = context.WriterFactory(context.HttpContext.Response.Body, selectedEncoding);
            var statusCode = context.HttpContext.Response.StatusCode;
            var rewrittenValue = new
            {
                status = IsSucceeded(statusCode),
                error = IsSucceeded(statusCode) ? null : new ErrorDescription((HttpStatusCode)statusCode),
                data = context.Object,
            };
            writer.Write(rewrittenValue);
            this.CreateJsonWriter(writer);
            await writer.FlushAsync();

        }

        private bool IsSucceeded(int statusCode)
        {
            // 204 is not an error but handled
            if (statusCode >= 400 || statusCode == 204) { return false; }
            return true;
        }
    }

Answer 1

我没有详细查看你的实现（看起来很复杂，你想达到什么目的？），但你可以像使用 [=12] 一样使用 UseControllers() =] 之前配置 MvcOptions 实例。例如：

services.AddControllers(options =>
{
    options.InputFormatters.Insert(0, new VcardInputFormatter());
    options.OutputFormatters.Insert(0, new VcardOutputFormatter());
})

这可能会解决您的问题 - 无需致电 AddMvc。

但是，错误 "Some services are not able to be constructed" 表明您缺少服务依赖项。错误消息会告诉您是哪一个。这是 .NET Core 3.1 中的新功能，服务提供者验证，您可以 read about in this blog post.