Newtonsoft json.net Deserialisierung NullReferenceException

Question

Ich habe eine einfache JSON mit WCF Rest Client generiert, aber wenn ich versuche, eine Antwort deserialize ich bekomme einen Fehler NullReferenceException in JSON.Net. Ich habe folgende JSON:

{"Code":-2146232800,"ExceptionType":"IOException","Message":"Msg","Stacktrace":"Some"} 

Und folgende Klasse:

[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; } 
} 

Dann habe ich deserialisieren es:

const string text = "{\"Code\":-2146232800,\"ExceptionType\":\"IOException\",\"Message\":\"Msg\",\"Stacktrace\":\"Some\"}"; 
var obj = JsonConvert.DeserializeObject<FileUploadError>(text); 

Und subj Fehler. Reproduziert in neuer Konsolenanwendung, die ich bei Bedarf bereitstellen kann. JSON ist sehr einfach, warum bekomme ich diesen Fehler?

Probe: https://dotnetfiddle.net/76FJd0

Stacktrace:

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) 

Answer 1

Sie benötigen einen öffentlichen parameterlosen Konstruktor auf Ihre FileUploadError Klasse hinzuzufügen:

public class FileUploadError 
{ 
    public FileUploadError() 
    { 
    } 

Oder könnten Sie es privat machen und [JsonConstructor] verwenden :

public class FileUploadError 
{ 
    [JsonConstructor] 
    private FileUploadError() 
    { 
    } 

Oder lassen Sie es privat und deserialisieren mit ConstructorHandling = ConstructorHandling.AllowNonPublicDefaultConstructor:

var settings = new JsonSerializerSettings 
{ 
    ConstructorHandling = ConstructorHandling.AllowNonPublicDefaultConstructor 
}; 
var obj = JsonConvert.DeserializeObject<FileUploadError>(text, settings); 

mit:

public class FileUploadError 
{ 
    private FileUploadError() 
    { 
    }