ASP.Net Webmethod：如何用继承类反序列化参数？

Question

我在标有 [ScriptService] 的类中定义了一个 WebMethod，如下所示：

[WebMethod(enableSession: false), ScriptMethod(UseHttpGet = false, ResponseFormat = ResponseFormat.Json)]
public static JsonResult ReportApplicationActivity(JsonApplicationActivityReport request, bool isTestUpload)
{ ... }

JsonApplicationActivityReport 类型的参数是一个抽象基类，可能是许多（一级）子类之一。 问题：当我从 WPF 客户端调用此 WebMethod 时，该方法永远不会被命中，并且在客户端抛出异常，说明类似于“内部服务器错误 (500)”。

我在 Global.asax 中的配置：

GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.SerializationBinder = new JsonApiUtils.InheritanceSerializationBinder();
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.TypeNameHandling = TypeNameHandling.All;

所以我试图告诉 JSON 序列化器使用自定义 SerializationBinder 来解决继承问题。它看起来像这样：

public class InheritanceSerializationBinder : DefaultSerializationBinder
    {
        public override Type BindToType(string assemblyName, string typeName)
        {
            switch (typeName)
            {
                case "JsonMeasurementActivityReport[]": return typeof(JsonMeasurementActivityReport[]);
                case "JsonMeasurementActivityReport": return typeof(JsonMeasurementActivityReport);
                case "JsonSimulationActivityReport[]": return typeof(JsonSimulationActivityReport[]);
                case "JsonSimulationActivityReport": return typeof(JsonSimulationActivityReport);
                default: return base.BindToType(assemblyName, typeName);
            }
        }
    }

但是 BindToType() 方法在请求期间永远不会被调用。 我还在 Web.config 中打开了跟踪，可以看到请求（每次调用 2 个，无论出于何种原因......）到达服务器，但 /trace.axd 中没有提供错误消息或任何对我有帮助的信息。

最后，这就是我的客户端代码的样子：

JsonApplicationActivityReport request = new JsonApplicationActivityReport () {...};
HttpWebRequest webRequest = GetWebRequest(Endpoints.ReportApplicationActivity);
using (var writer = webRequest.GetRequestStream())
{
    string jsonRequest = JsonConvert.SerializeObject(new { request = request, isTestUpload = isTestUpload }, Formatting.Indented, new JsonSerializerSettings {  TypeNameHandling = TypeNameHandling.All }); //also includes type information when serializing to JSON (required because the server expects an abstract class that has to be deserialized into the actual child activity class)
    byte[] requestData = Encoding.UTF8.GetBytes(jsonRequest);
    writer.Write(requestData, 0, requestData.Length);
}

var webResponse = (HttpWebResponse)webRequest.GetResponse();
var responseStream = new StreamReader(webResponse.GetResponseStream());

只要调用 GetResponse()，就会触发异常。

请告诉我我在这里缺少什么:)

Answer 1

WebService/ScriptService 不遵守您在Global.asax 中设置的序列化程序设置。它使用System.Web.Script.Serialization.JavaScriptSerializer，它被硬编码为WebServiceData，您对此没有太多控制权。

但是，它允许您注册继承自 JavaScriptConverter 的自定义 JavaScript 转换器。为此，您需要在 Web.config 文件中使用 system.web.extensions/scripting/webServices/jsonSerialization/converters 配置。

例如，假设您实现了JsonApplicationActivityReportConverter 来处理JsonApplicationActivityReport 类的反序列化。在这种情况下，配置如下所示

<configuration>
  <!-- ... -->
  <system.web.extensions>
    <scripting>
      <webServices>
        <jsonSerialization>
          <converters>
            <add name="JsonApplicationActivityReportConverter" type="YourApplicationNamespace.JsonApplicationActivityReportConverter, YourApplicationAssemblyName"/>
          </converters>
        </jsonSerialization>
      </webServices>
    </scripting>
  </system.web.extensions>
</configuration>

但是，缺点是您必须重新发明大部分反序列化以在您的 JsonApplicationActivityReportConverter 中正确处理此问题。作为一个起点，这个类看起来像......

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Web.Script.Serialization;

namespace YourApplicationNamespace    {
    public class JsonApplicationActivityReportConverter : JavaScriptConverter
    {
        public override object Deserialize(IDictionary<string, object> dictionary, Type type, JavaScriptSerializer serializer)
        {
            var typeName = (string) dictionary["$type"];
            var typeInfo = Type.GetType(typeName);
            var result = Activator.CreateInstance(typeInfo);

            foreach (var property in typeInfo.GetProperties(BindingFlags.Instance | BindingFlags.Public))
            {
                if (property.CanWrite && dictionary.ContainsKey(property.Name))
                {
                    property.SetValue(result, dictionary[property.Name]);
                }
            }

            return result;
        }

        public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer)
        {
            // Reverse the process here if the type is to be used the other direction
        }

        public override IEnumerable<Type> SupportedTypes
        {
            get { yield return typeof(JsonApplicationActivityReport); }
        }
    }
}