protobuf-net：枚举类型转换错误

Question

namespace MyNamespace                                               
{       

    public enum MyEnum
    {
        EnumName1 = 1,    
        EnumName2 = 2,
        ...

    [ProtoContract(Name=@"MyClassProto")]                                               
    [Serializable]                                                                                  
    public class MyClass : IExtensible                                              
    {                                                                                                                                           
        [ProtoMember(1, IsRequired = false, Name = @"MyEnumProperty", DataFormat = ProtoBuf.DataFormat.Default)]
        [System.ComponentModel.DefaultValue(1)]                                                     
        public MyEnum MyEnumProperty;                               
        ...



  var myObjectIn = new MyClass
  {
      MyEnumProperty = MyEnum.EnumName1,
      ...
  };

  MyClass myObjectOut;
  using (var stream = new MemoryStream())
  {
      ProtoBuf.Serializer.Serialize(stream, myObjectIn);
      stream.Seek(0, SeekOrigin.Begin);
      myObjectOut = ProtoBuf.Serializer.Deserialize<MyClass>(stream);
  }

System.InvalidCastException : Invalid cast from 'System.Int32' to 'MyNamespace.MyEnum'.

Answer 1

I am using protobuf-net v2.1.0, and depending on approach I get two distinct ProtoException s. Either No wire-value is mapped to the enum MyEnum , or No parameterless constructor found . Reasons are: the default int value 0 is not a constant in your enum type, or you haven't assigned a default value to it in a parameter constructor.

Workaround (logical or):

public enum MyEnum { EnumName1 = 1, EnumName2 = 2, @default = 0 }

or

public MyClass() { MyEnumProperty = MyEnum.EnumName1 }

From ECMA-334 C# Language Specification

1. An enum declaration that does not explicitly declare an underlying type has an underlying type of int. If the enum member is the first enum member declared in the enum type, its associated value is zero.
2. Enums are used for “multiple choice” scenarios, in which a runtime decision is made from a fixed number of choices that are known at compile-time

So, your enum with a runtime value you haven't defined as a compile-time constant, imo, is a bad enum.