c# - DataContractJsonSerializer 设置值扩展点

Question

using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Json;
using System.Text;

namespace ConsoleApplication1 {
  internal class Program {
    private static void Main(string[] args) {
      var pony = new Pony();
      var serializer = new DataContractJsonSerializer(pony.GetType());
      var example = @"{""Foo"":null}";
      var stream = new MemoryStream(Encoding.UTF8.GetBytes(example.ToCharArray()));
      stream.Position = 0;
      pony = (Pony) serializer.ReadObject(stream);
      // The previous line throws an exception.
    }
  }

  [DataContract]
  public class Pony {
    [DataMember]
    private int Foo { get; set; }
  }
}

有时，序列化会在将 Int32 设置为 null 时引发强制转换错误。 有什么方法可以连接到 Json 序列化器吗？

Answer 1

恕我直言，最好的办法是更改 Foo从 Int32 输入至 System.Nullable<Int32> 因为这最能反射(reflect)它的语义(如果它可以为空)但是如果你不能修改这个类并且如果使用 DataContractJsonSerializer对您来说不是义务，Json.NET有允许您执行此操作的扩展点(它也恰好是 better performing )。

例如，您可以编写自定义类型转换器:

internal class NullableIntConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(int);
    }

    public override object ReadJson(JsonReader reader, Type objectType, JsonSerializer serializer)
    {
        if (reader.Value == null)
        {
            return default(int);
        }
        return int.Parse(reader.Value.ToString());
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new System.NotImplementedException();
    }
}

可以这样注册和使用:

internal class Program
{
    private static void Main(string[] args)
    {
        var serializer = new JsonSerializer();
        serializer.Converters.Add(new NullableIntConverter());
        using (var reader = new StringReader(@"{""Foo"":null}"))
        using (var jsonReader = new JsonTextReader(reader))
        {
            var pony = serializer.Deserialize<Pony>(jsonReader);
            Console.WriteLine(pony.Foo);
        }
    }
}