[英]Newtonsoft json.net deserialization NullReferenceException
我有一個使用WCF Rest客戶端生成的簡單JSON,但是當我嘗試反序列化響應時,我在JSON.Net中收到錯誤NullReferenceException
。 我有以下JSON:
{"Code":-2146232800,"ExceptionType":"IOException","Message":"Msg","Stacktrace":"Some"}
下課:
[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; }
}
然后我反序化它:
const string text = "{\"Code\":-2146232800,\"ExceptionType\":\"IOException\",\"Message\":\"Msg\",\"Stacktrace\":\"Some\"}";
var obj = JsonConvert.DeserializeObject<FileUploadError>(text);
並得到subj錯誤。 在新的控制台應用程序中重現,如果需要,我可以提供。 JSON很簡單,為什么我收到這個錯誤?
示例: https : //dotnetfiddle.net/76FJd0
堆棧跟蹤:
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)
您需要向FileUploadError
類添加一個公共無參數構造函數:
public class FileUploadError
{
public FileUploadError()
{
}
或者,您可以將其[JsonConstructor]
私有並使用[JsonConstructor]
:
public class FileUploadError
{
[JsonConstructor]
private FileUploadError()
{
}
或者,將其保密並使用ConstructorHandling = ConstructorHandling.AllowNonPublicDefaultConstructor
反序列化:
var settings = new JsonSerializerSettings
{
ConstructorHandling = ConstructorHandling.AllowNonPublicDefaultConstructor
};
var obj = JsonConvert.DeserializeObject<FileUploadError>(text, settings);
有:
public class FileUploadError
{
private FileUploadError()
{
}
對於那些稍后翻滾的人,以及OP的具體案例已經解決。
以下是如何在發生錯誤消息時獲取更清晰的錯誤消息。
資料來源: https : //www.newtonsoft.com/json/help/html/SerializationErrorHandling.htm
var errors = new List<string>();
List<DateTime> c = JsonConvert.DeserializeObject<List<DateTime>>(
yourJsonHere,
new JsonSerializerSettings
{
Error = delegate(object sender, ErrorEventArgs args)
{
errors.Add(args.ErrorContext.Error.Message);
args.ErrorContext.Handled = true;
}
});
errors
將包含發生的錯誤列表! 適用於序列化和反 序列化 !
這樣做你會失去上下文! 因此,您可以將其設置為Handled = false
。
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