Question

代码如下：

using System.Diagnostics;
using System.IO;
using ProtoBuf;

namespace ProtoBufTest
{
    [ProtoContract]
    [ProtoInclude(13, typeof(BuildEvent))]
    public abstract class Event
    {
        [ProtoMember(1)]
        public int NodeId { get; set; }
    }

    [ProtoContract]
    public class BuildEvent : Event
    {
    }

    public class Program
    {
        static void Main(string[] args)
        {
            var ms = new MemoryStream();
            Serializer.SerializeWithLengthPrefix<object>(ms, new BuildEvent(), PrefixStyle.Base128);

            Debug.WriteLine(ms.Position);
            ms.Position = 0;

            var ev = Serializer.DeserializeWithLengthPrefix<BuildEvent>(ms, PrefixStyle.Base128);
            Debug.WriteLine(ev.ToString());
        }
    }
}

我正在使用protobuf-net 2.4.0。运行此代码会引发以下异常：

Unhandled Exception: ProtoBuf.ProtoException: No parameterless constructor found for ProtoBufTest.Event
   at ProtoBuf.Meta.TypeModel.ThrowCannotCreateInstance(Type type)
   at proto_4(Object , ProtoReader )
   at ProtoBuf.Serializers.CompiledSerializer.ProtoBuf.Serializers.IProtoSerializer.Read(Object value, ProtoReader source)
   at ProtoBuf.Meta.RuntimeTypeModel.Deserialize(Int32 key, Object value, ProtoReader source)
   at ProtoBuf.Meta.TypeModel.DeserializeWithLengthPrefix(Stream source, Object value, Type type, PrefixStyle style, Int32 expectedField, TypeResolver resolver, Int64& bytesRead, Boolean& haveObject, SerializationContext context)
   at ProtoBuf.Serializer.DeserializeWithLengthPrefix[T](Stream source, PrefixStyle style, Int32 fieldNumber)
   at ProtoBuf.Serializer.DeserializeWithLengthPrefix[T](Stream source, PrefixStyle style)
   at ProtoBufTest.Program.Main(String[] args) in C:\Work\ProtoBufTest\ProtoBufTest\Program.cs:line 30

Answer 1

此处使用<object>是不正确的；就是说“我知道类型-类型是object”。如果没有通用的情况，则应使用非通用的API-请参见Serializer.NonGeneric.*或使用RuntimeTypeModel.Default.*；然后它将通过该对象获得Type。

我会考虑是否应该让<object>自动切换到非通用模式。

为什么以下简单的C＃代码引发有关缺少的默认构造函数的ProtoException？

1 个答案: