使用多态对象数组的JSON反序列化

Question

我遇到了一个涉及多态对象数组的JSON反序列化问题。我尝试了这里和这里记录的序列化解决方案，它们对序列化非常有效，但在反序列化方面都失败了。

我的类结构如下:

IDable

[DataContract(IsReference=true)]
public abstract class IDable<T> {
    [DataMember]
    public T ID { get; set; }
}

观察组

[DataContract(IsReference=true)]
[KnownType(typeof(DescriptiveObservation))]
[KnownType(typeof(NoteObservation))]
[KnownType(typeof(NumericObservation))]
[KnownType(typeof(ScoredObservation))]
public class ObservationGroup : IDable<int> {
    [DataMember]
    public string Title { get; set; }
    [DataMember]
    public List<Observation> Observations { get; set; }
    [OnDeserializing]
    void OnDeserializing(StreamingContext context)
    {
        init();
    }
    public ObservationGroup()  {
        init();
    }
    private void init()
    {
        Observations = new List<Observation>();
        ObservationRecords = new List<ObservationRecord>();
    }
}

DescriptiveObservation

[DataContract(IsReference = true)]
public class DescriptiveObservation : Observation
{
    protected override ObservationType GetObservationType()
    {
        return ObservationType.Descriptive;
    }
}

NoteObservation

[DataContract(IsReference = true)]
public class NoteObservation : Observation
{
    protected override ObservationType GetObservationType()
    {
        return ObservationType.Note;
    }
}

NumericObservation

[DataContract(IsReference = true)]
public class NumericObservation : Observation
{
    [DataMember]
    public double ConstraintMaximum { get; set; }
    [DataMember]
    public double ConstraintMinimum { get; set; }
    [DataMember]
    public int PrecisionMaximum { get; set; }
    [DataMember]
    public int PrecisionMinimum { get; set; }
    [DataMember]
    public string UnitType { get; set; }
    protected override ObservationType GetObservationType()
    {
        return ObservationType.Numeric;
    }
}

ScoredObservation

[DataContract(IsReference = true)]
public class ScoredObservation : Observation {
    [DataMember]
    public int Value { get; set; }
    protected override ObservationType GetObservationType() {
        return ObservationType.Scored;
    }
}

我对使用内置的JavaScriptSerializer或Newtonsoft JSON库持中立态度。

序列化代码

var settings = new Newtonsoft.Json.JsonSerializerSettings();
settings.TypeNameHandling = Newtonsoft.Json.TypeNameHandling.Objects;
Newtonsoft.Json.JsonConvert.SerializeObject(AnInitializedScoresheet, Newtonsoft.Json.Formatting.None, settings);

反序列化代码

return Newtonsoft.Json.JsonConvert.DeserializeObject(returnedStringFromClient, typeof(Scoresheet));
//Scoresheet contains a list of observationgroups

我得到的错误是

"无法创建projectxcommon . datastore . observation类型的实例。"类型是接口或抽象类，不能实例化。"

任何帮助将非常感激!

Answer 1

您没有添加任何反序列化设置。您需要将TypeNameHandling设置为Object或All。

像这样:

JsonConvert.DeserializeObject(
    returnedStringFromClient, 
    typeof(Scoresheet), 
    new JsonSerializerSettings 
    { 
        TypeNameHandling = TypeNameHandling.Objects 
    });

文档:TypeNameHandling设置

Answer 2

使用这个JsonKnownTypes，方法类似:

[JsonConverter(typeof(JsonKnownTypesConverter<BaseClass>))]
[JsonKnownType(typeof(Base), "base")]
[JsonKnownType(typeof(Derived), "derived")]
public class Base
{
    public string Name;
}
public class Derived : Base
{
    public string Something;
}

现在当你序列化json对象将添加"$type"与"base"和"derived"值，它将用于反序列化

序列化列表示例:

[
    {"Name":"some name", "$type":"base"},
    {"Name":"some name", "Something":"something", "$type":"derived"}
]