Question

我正在尝试反序列化一个json响应，并且得到的值不能为null错误。

非常感谢任何帮助！我用这种方式反序列化了很多其他json字符串，并且从未遇到过这个错误。我不确定是什么导致了它。谢谢！

以下是对象的代码：

[Serializable]
public class LocationResponse
{
    public string authenticationResultCode { get; set; }
    public string brandLogoUri { get; set; }
    public string copyright { get; set; }
    public List<ResourceSet> resourceSets { get; set; }
    public int statusCode { get; set; }
    public string statusDescription { get; set; }
    public string traceId { get; set; }
}

[Serializable]
public class ResourceSet
{
    public int estimatedTotal { get; set; }
    public List<Resource> resources { get; set; }
}

[Serializable]
public class Resource
{
    //public string __type { get; set; }
    //public List<double> bbox { get; set; }
    public string name { get; set; }
    public Point point { get; set; }
    //public Address address { get; set; }
    //public string confidence { get; set; }
    //public string entityType { get; set; }
}

[Serializable]
public class Point
{
    public string type { get; set; }
    public List<double> coordinates { get; set; }
}

[Serializable]
public class Address
{
    public string countryRegion { get; set; }
    public string formattedAddress { get; set; }
}

反序列化的代码：

System.Web.Script.Serialization.JavaScriptSerializer ser = new System.Web.Script.Serialization.JavaScriptSerializer();
string json = "{\"authenticationResultCode\":\"ValidCredentials\",\"brandLogoUri\":\"http:\\/\\/dev.virtualearth.net\\/Branding\\/logo_powered_by.png\",\"copyright\":\"Copyright Â© 2011 Microsoft and its suppliers. All rights reserved. This API cannot be accessed and the content and any results may not be used, reproduced or transmitted in any manner without express written permission from Microsoft Corporation.\",\"resourceSets\":[{\"estimatedTotal\":1,\"resources\":[{\"__type\":\"Location:http:\\/\\/schemas.microsoft.com\\/search\\/local\\/ws\\/rest\\/v1\",\"bbox\":[33.177484847720336,35.531577579036423,33.235425613705445,35.623878963932327],\"name\":\"Qiryat Shemona, Israel\",\"point\":{\"type\":\"Point\",\"coordinates\":[33.206455230712891,35.577728271484375]},\"address\":{\"adminDistrict\":\"Northern\",\"countryRegion\":\"Israel\",\"formattedAddress\":\"Qiryat Shemona, Israel\",\"locality\":\"Qiryat Shemona\"},\"confidence\":\"High\",\"entityType\":\"PopulatedPlace\"}]}],\"statusCode\":200,\"statusDescription\":\"OK\",\"traceId\":\"NVM001351\"}";
LocationResponse response = ser.Deserialize<LocationResponse>(json);

我收到错误，我无法弄清楚代码的哪一部分或json给出了这个错误：异常详细信息：System.ArgumentNullException：Value不能为null。参数名称：type

如果有用，这是堆栈跟踪：

[ArgumentNullException: Value cannot be null.
Parameter name: type]
System.Activator.CreateInstance(Type type, Boolean nonPublic) +7468694
System.Web.Script.Serialization.ObjectConverter.ConvertDictionaryToObject(IDictionary`2 dictionary, Type type, JavaScriptSerializer serializer, Boolean throwOnError, Object& convertedObject) +406
System.Web.Script.Serialization.ObjectConverter.ConvertObjectToTypeInternal(Object o, Type type, JavaScriptSerializer serializer, Boolean throwOnError, Object& convertedObject) +71
System.Web.Script.Serialization.ObjectConverter.ConvertObjectToTypeMain(Object o, Type type, JavaScriptSerializer serializer, Boolean throwOnError, Object& convertedObject) +147
System.Web.Script.Serialization.ObjectConverter.ConvertObjectToType(Object o, Type type, JavaScriptSerializer serializer) +21
System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeInternal(Int32 depth) +181
System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeList(Int32 depth) +119
System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeInternal(Int32 depth) +210
System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeDictionary(Int32 depth) +422
System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeInternal(Int32 depth) +147
System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeList(Int32 depth) +119
System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeInternal(Int32 depth) +210
System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeDictionary(Int32 depth) +422
System.Web.Script.Serialization.JavaScriptObjectDeserializer.DeserializeInternal(Int32 depth) +147
System.Web.Script.Serialization.JavaScriptObjectDeserializer.BasicDeserialize(String input, Int32 depthLimit, JavaScriptSerializer serializer) +51
System.Web.Script.Serialization.JavaScriptSerializer.Deserialize(JavaScriptSerializer serializer, String input, Type type, Int32 depthLimit) +37
System.Web.Script.Serialization.JavaScriptSerializer.Deserialize(String input) +70

Answer 1

问题在于JSON中的__type字段。

阅读以下内容的答案：Problem with deserializing JSON on datamember “__type”似乎引用：the "__type" field has a special meaning for DataContractJsonSerializer, denoting the type to which the object should be deserialized.

从JSON中删除__type解决了这个问题。

一个选项，（如果您无法控制JSON），我刚刚使用JSON.NET库进行了测试，它按预期工作，反序列化，没有错误。

LocationResponse response = JsonConvert.DeserializeObject<LocationResponse>(json);

Answer 2

从堆栈跟踪中可以看到从System.Activator.CreateInstance（Type type，bool）方法抛出异常。
抛出它是因为反序列化器将null作为“type”传递给我上面提到的方法。

最有可能的情况是，因为反序列化器无法找到要将JSON反序列化的正确类型。尝试首先序列化LocationResponse类的实例，并将结果与您尝试反序列化的字符串进行比较。

Answer 3

这已经很晚了，但我遇到了同样的问题并通过向相关类添加默认构造函数并确保该类属性的setter是公共的来解决它。这解决了我的问题（同时存在于FastJson和JSON.net）。

万一有人遇到问题，上面的答案对他们没有帮助。

反序列化错误：值不能为空。参数名称：类型

3 个答案: