Could not create an instance of type T. Type is an interface or abstract class

在开发中定义了一个抽象类，序列号抽象类的子类时，出现如下问题：

Could not create an instance of type TestJsonConvert.IDevice. Type is an interface or abstract class and cannot be instantiated.

解决方法：

在JsonSerializerSettings中设置TypeNameHandling 属性为TypeNameHandling.Auto即可。如下所示：

public abstract class Business
{public string Name { get; set; }
}public class Hotel : Business
{public int Stars { get; set; }
}public class Stockholder
{public string FullName { get; set; }public IList<Business> Businesses { get; set; }
}Stockholder stockholder = new Stockholder
{FullName = "Steve Stockholder",Businesses = new List<Business>{new Hotel{Name = "Hudson Hotel",Stars = 4}}
};string jsonTypeNameAll = JsonConvert.SerializeObject(stockholder, Formatting.Indented, new JsonSerializerSettings
{TypeNameHandling = TypeNameHandling.All
});Console.WriteLine(jsonTypeNameAll);
// {
//   "$type": "Newtonsoft.Json.Samples.Stockholder, Newtonsoft.Json.Tests",
//   "FullName": "Steve Stockholder",
//   "Businesses": {
//     "$type": "System.Collections.Generic.List`1[[Newtonsoft.Json.Samples.Business, Newtonsoft.Json.Tests]], mscorlib",
//     "$values": [
//       {
//         "$type": "Newtonsoft.Json.Samples.Hotel, Newtonsoft.Json.Tests",
//         "Stars": 4,
//         "Name": "Hudson Hotel"
//       }
//     ]
//   }
// }string jsonTypeNameAuto = JsonConvert.SerializeObject(stockholder, Formatting.Indented, new JsonSerializerSettings
{TypeNameHandling = TypeNameHandling.Auto
});Console.WriteLine(jsonTypeNameAuto);
// {
//   "FullName": "Steve Stockholder",
//   "Businesses": [
//     {
//       "$type": "Newtonsoft.Json.Samples.Hotel, Newtonsoft.Json.Tests",
//       "Stars": 4,
//       "Name": "Hudson Hotel"
//     }
//   ]
// }// for security TypeNameHandling is required when deserializing
Stockholder newStockholder = JsonConvert.DeserializeObject<Stockholder>(jsonTypeNameAuto, new JsonSerializerSettings
{TypeNameHandling = TypeNameHandling.Auto
});Console.WriteLine(newStockholder.Businesses[0].GetType().Name);
// Hotel

总结

属性	值	描述
None	0	序列化类型时不要包含.NET类型名称。
Objects	1	序列化为JSON对象结构时包括.NET类型名称。
Arrays	2	序列化为JSON数组结构时包含.NET类型名称。
All	3	始终在序列化时包含.NET类型名称。
Auto	4	当序列化对象的类型与其声明的类型不同时，请包含.NET类型名称。请注意，默认情况下，这不包括根序列化对象。要在JSON中包含根对象的类型名称，必须使用SerializeObject（Object，Type，JsonSerializerSettings）或Serialize（JsonWriter，Object，Type）指定根类型对象。

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Could not create an instance of type T. Type is an interface or abstract class

总结

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