C# 如何使用Json格式化程序将抽象类传递给Asp.NETWebAPI？

基本上，我正在尝试使我的WebApi更通用：

型号：

public abstract class A {}
public class B : A { }

客户：

using (var client = new HttpClient())
{
    client.BaseAddress = new Uri("http://localhost:49611/");  
    var aList = List<A> { new B() };
    var response = await client.PostAsJsonAsync("api/a", aList);
}

然而，这对我不起作用

但是，作为测试，如果我直接使用JsonConverter，我确实看到

TypeNameHandling.Auto

工作正常：

var aList = List<A> { new B() };
var settings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.Auto };
var str = JsonConvert.SerializeObject(aList, Formatting.Indented, settings);
var obj = JsonConvert.DeserializeObject<List<A>>(str, settings);

这是我的网站配置：

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // Web API configuration and services
        // Configure Web API to use only bearer token authentication.
        config.SuppressDefaultHostAuthentication();
        config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));

        // Web API routes
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );

        config.formatters.clear();
        config.Formatters.Add(new CustomJsonFormatter() { SerializerSettings = new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.Auto } });
    }
}

有人有线索吗

更新和解决方案：

好吧，经过一番挣扎，我自己找到了答案。问题出在使用

clien.PostAsJsonAsync

的客户端请求中。我必须使用另一个带有格式化程序参数的函数

PostAsync

来添加

typenameholling.Auto

，如下所示

var formatter = new JsonMediaTypeFormatter() { SerializerSettings = new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.Auto } };
var response = await client.PostAsync("api/a", aList, formatter);

在

WebApiConfig.cs

中，使用此函数和

typenameholling.Auto

，可以正确地反序列化和序列化派生类

public class CustomJsonFormatter : JsonMediaTypeFormatter
{
    public override Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext)
    {
        try
        {
            Encoding effectiveEncoding = SelectCharacterEncoding(content == null ? null : content.Headers);

            if (!UseDataContractJsonSerializer)
            {
                using (JsonTextWriter jsonTextWriter = new JsonTextWriter(new StreamWriter(writeStream, effectiveEncoding)) { CloseOutput = false })
                {
                    if (Indent)
                    {
                        jsonTextWriter.Formatting = Newtonsoft.Json.Formatting.Indented;
                    }

                    JsonSerializer jsonSerializer = JsonSerializer.Create(this.SerializerSettings);
                    jsonSerializer.Serialize(jsonTextWriter, value, type); //NOTE: passing in 'type' here
                    jsonTextWriter.Flush();
                }
            }
            else
            {
                return base.WriteToStreamAsync(type, value, writeStream, content, transportContext);
            }

            return TaskHelpers.Completed();
        }
        catch (Exception e)
        {
            return TaskHelpers.FromError(e);
        }
    }
}

internal class TaskHelpers
{
    private static readonly Task _defaultCompleted = FromResult<AsyncVoid>(default(AsyncVoid));

    /// <summary>
    /// Used as the T in a "conversion" of a Task into a Task{T}
    /// </summary>
    private struct AsyncVoid
    {
    }

    internal static Task<TResult> FromResult<TResult>(TResult result)
    {
        TaskCompletionSource<TResult> tcs = new TaskCompletionSource<TResult>();
        tcs.SetResult(result);
        return tcs.Task;
    }

    /// <summary>
    /// Returns an error task. The task is Completed, IsCanceled = False, IsFaulted = True
    /// </summary>
    internal static Task FromError(Exception exception)
    {
        return FromError<AsyncVoid>(exception);
    }

    /// <summary>
    /// Returns an error task of the given type. The task is Completed, IsCanceled = False, IsFaulted = True
    /// </summary>
    /// <typeparam name="TResult"></typeparam>
    internal static Task<TResult> FromError<TResult>(Exception exception)
    {
        TaskCompletionSource<TResult> tcs = new TaskCompletionSource<TResult>();
        tcs.SetException(exception);
        return tcs.Task;
    }

    /// <summary>
    /// Returns a completed task that has no result. 
    /// </summary>        
    internal static Task Completed()
    {
        return _defaultCompleted;
    }
}

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        // Web API configuration and services
        // Configure Web API to use only bearer token authentication.
        config.SuppressDefaultHostAuthentication();
        config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));

        // Web API routes
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );

        config.formatters.clear();
        config.Formatters.Add(new CustomJsonFormatter() { SerializerSettings = new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.Auto } });
    }
}

var formatter = new JsonMediaTypeFormatter() { SerializerSettings = new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.Auto } };
var response = await client.PostAsync("api/a", aList, formatter);