我有一个 Newtonsoft JSON.NET JsonConverter
来帮助反序列化类型为抽象类的属性。它的要点是这样的:
public class PetConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(Animal);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
JObject jsonObject = JObject.Load(reader);
if (jsonObject["Lives"] != null) return jsonObject.ToObject<Cat>(serializer);
if (jsonObject["StopPhrase"] != null) return jsonObject.ToObject<Parrot>(serializer);
return null;
}
public override bool CanWrite { get { return false; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{ throw new NotImplementedException(); }
}
这是它处理的类:
public abstract class Animal
{ }
public class Cat : Animal
{
public int Lives { get; set; }
}
public class Parrot : Animal
{
public string StopPhrase { get; set; }
}
public class Person
{
[JsonConverter(typeof(PetConverter))]
public Animal Pet { get; set; }
}
这在反序列化具有非空 Pet
的 Person
时工作正常。但是,如果 Pet
为 null,则 ReadJson
方法会在第一行中断并出现此 JsonReaderException
:
An exception of type 'Newtonsoft.Json.JsonReaderException' occurred in Newtonsoft.Json.dll but was not handled in user code
Additional information: Error reading JObject from JsonReader. Current JsonReader item is not an object: Null. Path 'Pet', line 1, position 11.
我检查过 the Custom JsonConverter文档,但它仅仅是关于一个编写转换器。我尝试了以下方法:
if (reader.Value == null) return null; // this inverts the [Test] results
但后来我得到:
JsonSerializationException: Additional text found in JSON string after finishing deserializing object.
对于属性被填充的情况。
简而言之,处理这种情况的正确方法是什么?
为了完整起见,这里有一些单元测试可以证明手头的问题:
[TestFixture]
public class JsonConverterTests
{
[Test]
public void Cat_survives_serialization_roundtrip()
{
var person = new Person { Pet = new Cat { Lives = 9 } };
var serialized = JsonConvert.SerializeObject(person);
var deserialized = JsonConvert.DeserializeObject<Person>(serialized);
Assert.That(deserialized.Pet, Is.InstanceOf<Cat>());
Assert.That((deserialized.Pet as Cat).Lives, Is.EqualTo(9));
}
[Test]
public void Parrot_survives_serialization_roundtrip()
{
var person = new Person { Pet = new Parrot { StopPhrase = "Lorrie!" } };
var serialized = JsonConvert.SerializeObject(person);
var deserialized = JsonConvert.DeserializeObject<Person>(serialized);
Assert.That(deserialized.Pet, Is.InstanceOf<Parrot>());
Assert.That((deserialized.Pet as Parrot).StopPhrase, Is.EqualTo("Lorrie!"));
}
[Test]
public void Null_property_does_not_break_converter()
{
var person = new Person { Pet = null };
var serialized = JsonConvert.SerializeObject(person);
var deserialized = JsonConvert.DeserializeObject<Person>(serialized);
Assert.That(deserialized.Pet, Is.Null);
}
}
最佳答案
在写问题的时候,特别是在写“我试过什么”的时候,我找到了一个可能的解决方案:
if (reader.TokenType == JsonToken.Null) return null;
我发布这个有两个原因:
- 如果它足够好,它可能会帮助其他人解决同样的问题。
- 我可能会从其他人的回答中了解到更好的、有竞争力的解决方案。
FWIW,这里是完整的 JsonConverter,用于对类型为抽象类的属性进行非常基本的反序列化处理:
public class PetConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(Animal);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (reader.TokenType == JsonToken.Null) return null;
JObject jsonObject = JObject.Load(reader);
if (jsonObject["Lives"] != null) return jsonObject.ToObject<Cat>(serializer);
if (jsonObject["StopPhrase"] != null) return jsonObject.ToObject<Parrot>(serializer);
return null;
}
public override bool CanWrite { get { return false; } }
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
关于c# - 在自定义 JsonConverter 的 ReadJson 方法中处理空对象,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/34185295/