我有一个用WCF Rest客户端生成的简单JSON，但是当我尝试反序列化响应时NullReferenceException，JSON.Net中出现错误。我有以下JSON：
{"Code":-2146232800,"ExceptionType":"IOException","Message":"Msg","Stacktrace":"Some"}
和下课：
[DataContract]
public class FileUploadError
{
public FileUploadError(Exception exception)
{
Code = exception.HResult;
ExceptionType = exception.GetType().Name;
Message = GetMessage(exception);
Stacktrace = exception.StackTrace;
if (exception.Data.Count > 0)
{
Data = string.Join(Environment.NewLine, exception.Data.Cast<DictionaryEntry>().Select(x => x.Key + "=" + x.Value));
}
}
private string GetMessage(Exception exception)
{
if (exception.InnerException == null)
{
return exception.Message;
}
const string delimiter = "->";
var sb = new StringBuilder(1024);
for (var ex = exception; ex != null; ex = ex.InnerException)
{
sb.Append(ex.Message).Append(delimiter);
}
sb.Length -= delimiter.Length;
return sb.ToString();
}
[DataMember(IsRequired = true)]
[JsonProperty("Code", NullValueHandling = NullValueHandling.Ignore)]
public int Code { get; set; }
[DataMember(IsRequired = true)]
[JsonProperty("ExceptionType", NullValueHandling = NullValueHandling.Ignore)]
public string ExceptionType { get; set; }
[DataMember(EmitDefaultValue = false)]
[JsonProperty("Message", NullValueHandling = NullValueHandling.Ignore)]
public string Message { get; set; }
[DataMember(EmitDefaultValue = false)]
[JsonProperty("Stacktrace", NullValueHandling = NullValueHandling.Ignore)]
public string Stacktrace { get; set; }
[DataMember(EmitDefaultValue = false)]
[JsonProperty("Data", NullValueHandling = NullValueHandling.Ignore)]
public string Data { get; set; }
}
然后我反序列化它：
const string text = "{\"Code\":-2146232800,\"ExceptionType\":\"IOException\",\"Message\":\"Msg\",\"Stacktrace\":\"Some\"}";
var obj = JsonConvert.DeserializeObject<FileUploadError>(text);
并得到subj错误。转载在新的控制台应用程序中，如有需要，我可以提供。JSON非常简单，为什么会出现此错误？
范例：https：//dotnetfiddle.net/76FJd0
堆栈跟踪：
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.
at FileUploadError..ctor(Exception exception) in d:\Windows\Temp\nclgvim3.0.cs:line 28
--- End of inner exception stack trace ---
at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.ConstructorInfo.Invoke(Object[] parameters)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObjectFromNonDefaultConstructor(JsonReader reader, JsonObjectContract contract, JsonProperty containerProperty, ConstructorInfo constructorInfo, String id)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings)
at Program.Main(String[] args)
您需要在类中添加一个公共的无参数构造函数FileUploadError：
public class FileUploadError
{
public FileUploadError()
{
}
或者，您可以将其设为私有并使用[JsonConstructor]：
public class FileUploadError
{
[JsonConstructor]
private FileUploadError()
{
}
或者，将其保留为私有并反序列化ConstructorHandling = ConstructorHandling.AllowNonPublicDefaultConstructor：
var settings = new JsonSerializerSettings
{
ConstructorHandling = ConstructorHandling.AllowNonPublicDefaultConstructor
};
var obj = JsonConvert.DeserializeObject<FileUploadError>(text, settings);
和：
public class FileUploadError
{
private FileUploadError()
{
}
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