JSON.net(反)序列化未类型化的属性
本文关键字:类型化 属性 序列化 net JSON | 更新日期: 2023-09-27 18:00:12
假设我有一个这样的类:
public class Example {
public int TypedProperty { get; set; }
public object UntypedProperty { get; set; }
}
假设有人走过来写下:
var example = new Example
{
TypedProperty = 5,
UntypedProperty = Guid.NewGuid()
}
如果我用JsonConvert.SerializeObject(example)
串行化,我会得到
{
"TypedProperty": 5,
"UntypedProperty": "24bd733f-2ade-4374-9db6-3c9f3d97b12c"
}
理想情况下,我想得到这样的东西:
{
"TypedProperty": 5,
"UntypedProperty":
{
"$type": "System.Guid,mscorlib",
"$value": "24bd733f-2ade-4374-9db6-3c9f3d97b12c"
}
}
但是TypeNameHandling
在这种情况下不起作用。如何(反)序列化未类型化的属性?
如果用TypeNameHandling.All
或TypeNameHandling.Auto
序列化类,则当CCD_ 5属性将被序列化为JSON容器(对象或数组)时,JSON.NET应该通过将JSON文件中的类型信息存储在CCD_。但是,在UntypedProperty
被序列化为JSON基元(字符串、数字或布尔值)的情况下,这是不起作用的,因为正如您所指出的,JSON基元没有机会包含"$type"
属性。
解决方案是,当序列化具有类型object
属性的类型时,按照这个答案的行,序列化可以封装类型信息的基元值的包装器类。这里有一个自定义的JSON转换器,它注入了这样一个包装器:
public class UntypedToTypedValueConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
throw new NotImplementedException("This converter should only be applied directly via ItemConverterType, not added to JsonSerializer.Converters");
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (reader.TokenType == JsonToken.Null)
return null;
var value = serializer.Deserialize(reader, objectType);
if (value is TypeWrapper)
{
return ((TypeWrapper)value).ObjectValue;
}
return value;
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
if (serializer.TypeNameHandling == TypeNameHandling.None)
{
Console.WriteLine("ObjectItemConverter used when serializer.TypeNameHandling == TypeNameHandling.None");
serializer.Serialize(writer, value);
}
// Handle a couple of simple primitive cases where a type wrapper is not needed
else if (value is string)
{
writer.WriteValue((string)value);
}
else if (value is bool)
{
writer.WriteValue((bool)value);
}
else
{
var contract = serializer.ContractResolver.ResolveContract(value.GetType());
if (contract is JsonPrimitiveContract)
{
var wrapper = TypeWrapper.CreateWrapper(value);
serializer.Serialize(writer, wrapper, typeof(object));
}
else
{
serializer.Serialize(writer, value);
}
}
}
}
abstract class TypeWrapper
{
protected TypeWrapper() { }
[JsonIgnore]
public abstract object ObjectValue { get; }
public static TypeWrapper CreateWrapper<T>(T value)
{
if (value == null)
return new TypeWrapper<T>();
var type = value.GetType();
if (type == typeof(T))
return new TypeWrapper<T>(value);
// Return actual type of subclass
return (TypeWrapper)Activator.CreateInstance(typeof(TypeWrapper<>).MakeGenericType(type), value);
}
}
sealed class TypeWrapper<T> : TypeWrapper
{
public TypeWrapper() : base() { }
public TypeWrapper(T value)
: base()
{
this.Value = value;
}
public override object ObjectValue { get { return Value; } }
public T Value { get; set; }
}
然后使用[JsonConverter(typeof(UntypedToTypedValueConverter))]
:将其应用于您的类型
public class Example
{
public int TypedProperty { get; set; }
[JsonConverter(typeof(UntypedToTypedValueConverter))]
public object UntypedProperty { get; set; }
}
如果你不能以任何方式修改Example
类来添加这个属性(你的评论这个类不是我的,可以修改),你可以为转换器注入一个自定义的合约解析器:
public class UntypedToTypedPropertyContractResolver : DefaultContractResolver
{
readonly UntypedToTypedValueConverter converter = new UntypedToTypedValueConverter();
// As of 7.0.1, Json.NET suggests using a static instance for "stateless" contract resolvers, for performance reasons.
// http://www.newtonsoft.com/json/help/html/ContractResolver.htm
// http://www.newtonsoft.com/json/help/html/M_Newtonsoft_Json_Serialization_DefaultContractResolver__ctor_1.htm
// "Use the parameterless constructor and cache instances of the contract resolver within your application for optimal performance."
// See also https://stackoverflow.com/questions/33557737/does-json-net-cache-types-serialization-information
static UntypedToTypedPropertyContractResolver instance;
// Explicit static constructor to tell C# compiler not to mark type as beforefieldinit
static UntypedToTypedPropertyContractResolver() { instance = new UntypedToTypedPropertyContractResolver(); }
public static UntypedToTypedPropertyContractResolver Instance { get { return instance; } }
protected override JsonObjectContract CreateObjectContract(Type objectType)
{
var contract = base.CreateObjectContract(objectType);
foreach (var property in contract.Properties.Concat(contract.CreatorParameters))
{
if (property.PropertyType == typeof(object)
&& property.Converter == null)
{
property.Converter = property.MemberConverter = converter;
}
}
return contract;
}
}
并按如下方式使用:
var settings = new JsonSerializerSettings
{
TypeNameHandling = TypeNameHandling.Auto,
ContractResolver = UntypedToTypedPropertyContractResolver.Instance,
};
var json = JsonConvert.SerializeObject(example, Formatting.Indented, settings);
var example2 = JsonConvert.DeserializeObject<Example>(json, settings);
在这两种情况下,创建的JSON看起来都像:
{ "TypedProperty": 5, "UntypedProperty": { "$type": "Question38777588.TypeWrapper`1[[System.Guid, mscorlib]], Tile", "Value": "e2983c59-5ec4-41cc-b3fe-34d9d0a97f22" } }
Lookup SerializeWithJsonConverters.htm和ReadingWritingJSON。电话:JsonConvert.SerializeObject(example, new ObjectConverter());
class ObjectConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(Example);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
throw new NotImplementedException();
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
Example e = (Example)value;
writer.WriteStartObject();
writer.WritePropertyName("TypedProperty");
writer.WriteValue(e.TypedProperty);
writer.WritePropertyName("UntypedProperty");
writer.WriteStartObject();
writer.WritePropertyName("$type");
writer.WriteValue(e.UntypedProperty.GetType().FullName);
writer.WritePropertyName("$value");
writer.WriteValue(e.UntypedProperty.ToString());
writer.WriteEndObject();
writer.WriteEndObject();
}
}