为什么我使用KnownType属性错误？

Question

我试图从谷歌api反序列化一个json响应,所以我想我会定义几个类来帮助它:

[DataContract]
public class DetectionResult:ResponseData
{
    [DataMember(Name="language")]
    public string Language
    { get; set; }

    [DataMember(Name="isReliable")]
    public bool IsReliable
    { get; set; }

    [DataMember(Name="confidence")]
    public double Confidence
    {get;set;}
}

[DataContract]
public abstract class ResponseData
{

    [DataMember(Name = "error")]
    public TranslationError Error
    { get; set; }

}

[DataContract]
public class TranslationError
{
    [DataMember(Name="code")]
    public int Code
    { get; set; }

    [DataMember(Name="message" )]
    public int Message
    { get; set; }
}


[DataContract]
[KnownType(typeof(DetectionResult))]
public class RequestResult
{
    [DataMember(Name="responseStatus")]
    public int ResponseStatus
    { get; set; }

    [DataMember(Name="responseDetails")]
    public string ResponseDetails
    { get; set; }

    [DataMember(Name = "responseData")]
    public ResponseData Response
    { get; set; }
}

我提出请求后得到的回复是:

{"responseData": {"language":"en","isReliable":false,"confidence":0.114892714}, "responseDetails": null, "responseStatus": 200}

并使用此代码反序列化它:

HttpWebResponse response = (HttpWebResponse)request.GetResponse();
  using (Stream stream = response.GetResponseStream())
        {
            DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(RequestResult));

            RequestResult result = (RequestResult)serializer.ReadObject(stream);                

            stream.Close();
        }

但我得到一个例外,说明"无法创建一个抽象类".难道它不知道DetectionResult类并正确反序列化吗？

Answer 1

在您的响应数据中,无法推断出具体类型.未在响应中指定要反序列化的类型.

来自MSDN:

为了保留类型标识,在将复杂类型序列化为JSON时,可以添加"类型提示",并且反序列化器可以识别提示并采取相应的操作."类型提示"是一个JSON键/值对,键名为"__type"(两个下划线后跟单词"type").该值是"DataContractName:DataContractNamespace"形式的JSON字符串(第一个冒号的所有内容都是名称).使用前面的示例,"Circle"可以按如下方式序列化.

http://msdn.microsoft.com/en-us/library/bb412170.aspx

请参阅与多态性相关的部分.