我如何为这个特定的类编写自定义的 protobuf-net 序列化器

Question

我正在尝试编写一个自定义的 protobuf-net 序列化器，以将

object

类型的属性放入线路中。

[ProtoContract(Serializer=typeof(ChangeRecordSerializer))]
public class ChangeRecord
{
   public object NewValue {get;set;}
}

这就是我现在的位置：

public class ChangeRecordSerializer : ISerializer<ChangeRecord>
{
   public void Write(ref ProtoWriter.State state, ChangeRecord value)
   {
      state.WriteString(1, value.NewValue.GetType().FullName;
      // how to serialize value.NewValue???
   }

   public void Read(ref ProtoReader.State state, ChangeRecord value)
   {
      int num = 0;
      string typeName = null;
      while ((num = state.ReadFieldHeader()) > 0)
      {
         switch (num)
         {
            case 1:
               typeName = state.ReadString();
               break;

            case 2:
               var type = Type.GetType(typeName);
               // how to read value.NewValue???
               break;
         }
      }
   }

   public SerializerFeatures Features => SerializerFeatures.CategoryMessage | SerializerFeatures.WireTypeString;
}

如何实现这两行注释掉的代码？

Answer 1

使用自定义序列化器的问题是（至少目前）一旦达到该级别：您需要保持在该级别 - 这意味着：您不能仅仅让序列化器处理所有预期的类型：它期望你从那里向下明确表达，这会变得非常尴尬。如果这是我，我只会使用代理人，让代理人与受歧视的工会“类似”地工作。这不需要很昂贵；考虑：

using ProtoBuf;

Show(32);
Show("abc");
Show(new Foo { Bar = "banana" });

static void Show(object value)
{
    var obj = new ChangeRecord { NewValue = value };
    var clone = Serializer.DeepClone(obj);
    Console.WriteLine($"{obj.NewValue} => {clone.NewValue}");
}


[ProtoContract(Surrogate = typeof(ChangeRecordSurrogate))]
public class ChangeRecord
{
    public object? NewValue { get; set; }
}


[ProtoContract]
public class Foo
{
    [ProtoMember(1)]
    public string? Bar { get; set; }
    public override string ToString() => $"Foo: {Bar}";
}


[ProtoContract]
struct ChangeRecordSurrogate
{
    public static implicit operator ChangeRecordSurrogate(ChangeRecord value)
        => new ChangeRecordSurrogate { Value = value?.NewValue };
    public static implicit operator ChangeRecord(ChangeRecordSurrogate value)
        => new ChangeRecord { NewValue = value.Value! };

    public object? Value { get; set; }

    [ProtoMember(1)]
    public int? ValueInt32
    {
        get => Value is int x ? x : default;
        set => Value = value;
    }

    [ProtoMember(2)]
    public string? ValueString
    {
        get => Value as string;
        set => Value = value;
    }

    [ProtoMember(3)]
    public Foo? ValueFoo
    {
        get => Value as Foo;
        set => Value = value;
    }
}