Newtonsoft.Json，填充字典失败 [英] Newtonsoft.Json, Populate Dictionary failed

问题描述

  var serializeSettings = new JsonSerializerSettings 
我将序列化一个字典到json by Newtonsoft.json {
 TypeNameHandling = TypeNameHandling.All，
 TypeNameAssemblyFormat = FormatterAssemblyStyle.Full，
 Formatting = Formatting.Indented 
}; 
 var serializedObject = JsonConvert.SerializeObject（dic，serializeSettings）; 
  

此代码生成一个这样的json：

  {
$ type：System.Collections.Generic.Dictionary`2 [[System.Guid，mscorlib，Version = 4.0.0.0，Culture = neutral，PublicKeyToken = b77a5c561934e089]，[System.String，mscorlib，Version = 4.0.0.0，Culture = neutral，PublicKeyToken = b77a5c561934e089]]，mscorlib，Version = 4.0.0.0，Culture = neutral，PublicKeyToken = b77a5c561934e089，
9648af76 -7986-4b34-8b2c-97b2345769ef：测试
} 
  

我尝试通过此代码将json反序列化为字典：

  var newDic = new Dictionay< Guid，string>（）; 
 var deserializeSettings = new JsonSerializerSettings 
 {
 TypeNameHandling = TypeNameHandling.All，
 TypeNameAssemblyFormat = FormatterAssemblyStyle.Full，
 Formatting = Formatting.Indented 
} 
 JsonConvert.PopulateObject（serializedObject，newDic，deserializeSettings）; 
  

但是发生这种异常：

无法将字符串'$ type'转换为字典键类型'System.Guid'。创建一个TypeConverter以将其从字符串转换为键类型对象。路径'$ type'，行2，位置10。

在Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateDictionary（IDictionary dictionary，JsonReader reader，JsonDictionaryContract contract，JsonProperty containerProperty，在Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Populate（JsonReader reader，Object target）中

在Newtonsoft.Json.JsonSerializer.PopulateInternal（JsonReader reader，Object target）

在Newtonsoft.Json.JsonSerializer.Populate（JsonReader reader，Object target）

$ Newtonsoft.Json.JsonConvert.PopulateObject（String value，Object target，JsonSerializerSettings设置）中的
$ b

我写这样的GuidConverter并使用它。但不工作

  public class GuidConverter：JsonConverter 
 {
 public override bool CanConvert（Type objectType）
 {
 return objectType.IsAssignableFrom（typeof（Guid））; 
 
 
 public override object ReadJson（JsonReader reader，Type objectType，object existingValue，JsonSerializer serializer）
 {
 try 
 {
 return serializer.Deserialize<&的Guid GT;（读取器）; 
} 
 catch 
 {
 return Guid.Empty; 
} 
} 
 
 public override void WriteJson（JsonWriter writer，object value，JsonSerializer serializer）
 {
 serializer.Serialize（writer，value）; 
} 
} 
  

编辑： p>

我发现我的问题。将代码更改为序列化json到Dictionary<字符串，字符串>现在生成的字典中的第一个项目是：

  Kay：$ type
值： System.Collections.Generic.Dictionary`2 [[System.Guid，mscorlib，Version = 4.0.0.0，Culture = neutral，PublicKeyToken = b77a5c561934e089]，[System.String，mscorlib，Version = 4.0.0.0，Culture = neutral，PublicKeyToken = b77a5c561934e089]]，mscorlib，Version = 4.0.0.0，Culture = neutral，PublicKeyToken = b77a5c561934e089
  

为什么？

解决方案

问题是指定< a href =http://www.newtonsoft.com/json/help/html/P_Newtonsoft_Json_JsonSerializer_TypeNameHandling.htm =nofollow> TypeNameHandling = TypeNameHandling.All 当序列化你的字典。这将导致元数据$ type属性作为字典中的第一个对象发布：

  {
$ type：System.Collections.Generic.Dictionary`2 [[System.Guid，mscorlib，Version = 2.0.0.0，Culture =中性，PublicKeyToken = b77a5c561934e089]，[System.String，mscorlib，Version = 2.0.0.0，Culture = neutral，PublicKeyToken = b77a5c561934e089]]，mscorlib，Version = 2.0.0.0，Culture = neutral，PublicKeyToken = b77a5c561934e089，
9648af76-7986-4b34-8b2c-97b2345769ef：Test
} 
  

当使用 DeserializeObject ，当构造相应的c＃对象时，该令牌通常由Json.NET使用。但是您正在使用 PopulateObject 在预先分配的字典上。因此，元数据属性在构建期间不会消耗，而Json.NET会尝试将其添加到字典中，并失败。

解决方案设置 MetadataPropertyHandling = MetadataPropertyHandling.ReadAhead 在 deserializeSettings 。这样做会导致$ type属性无条件地被使用或忽略（如适用）：

  var deserializeSettings = new JsonSerializerSettings 
 {
 TypeNameHandling = TypeNameHandling.All，
 TypeNameAssemblyFormat = FormatterAssemblyStyle.Full，
 Formatting = Formatting.Indented，
 MetadataPropertyHandling = MetadataPropertyHandling.ReadAhead 
}; 
 JsonConvert.PopulateObject（serializedObject，newDic，deserializeSettings）; 
  

请注意，从发行说明，使用此设置的内存使用情况和速度。

或，如果您无条件地在JSON中需要元数据类型信息您可以使用 TypeNameHandling = TypeNameHandling.Auto 序列化，并且只会发布多态类型的类型信息，您的 Dictionary< Guid，string> 不是。

I serialize a dictionary to json by Newtonsoft.json and bellow code :

var serializeSettings = new JsonSerializerSettings
        {
            TypeNameHandling = TypeNameHandling.All,
            TypeNameAssemblyFormat = FormatterAssemblyStyle.Full,
            Formatting = Formatting.Indented
        };
        var serializedObject = JsonConvert.SerializeObject(dic, serializeSettings);

this code generate a json like this :

{
  "$type": "System.Collections.Generic.Dictionary`2[[System.Guid, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]], mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089",
  "9648af76-7986-4b34-8b2c-97b2345769ef": "Test"
}

I try to deserialize json to dictionary by this code :

var newDic = new Dictionay<Guid,string>();
var deserializeSettings = new JsonSerializerSettings
{
    TypeNameHandling = TypeNameHandling.All,
    TypeNameAssemblyFormat = FormatterAssemblyStyle.Full,
    Formatting = Formatting.Indented
}
JsonConvert.PopulateObject(serializedObject, newDic, deserializeSettings);

But this exception occurs :

Could not convert string '$type' to dictionary key type 'System.Guid'. Create a TypeConverter to convert from the string to the key type object. Path '$type', line 2, position 10.

at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateDictionary(IDictionary dictionary, JsonReader reader, JsonDictionaryContract contract, JsonProperty containerProperty, String id)

at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Populate(JsonReader reader, Object target)

at Newtonsoft.Json.JsonSerializer.PopulateInternal(JsonReader reader, Object target)

at Newtonsoft.Json.JsonSerializer.Populate(JsonReader reader, Object target)

at Newtonsoft.Json.JsonConvert.PopulateObject(String value, Object target, JsonSerializerSettings settings)

I write GuidConverter like this and use it. but not work

public class GuidConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType.IsAssignableFrom(typeof(Guid));
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        try
        {
            return serializer.Deserialize<Guid>(reader);
        }
        catch
        {
            return Guid.Empty;
        }
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        serializer.Serialize(writer, value);
    }
}

EDIT:

I found my problem. Change code to deserialize json to Dictionary< string, string > and now First item in generated dictionary is :

Kay: "$type"
Value : "System.Collections.Generic.Dictionary`2[[System.Guid, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]], mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"

Why??

解决方案

The problem is that you have specified TypeNameHandling = TypeNameHandling.All when serializing your dictionary. This causes a metadata "$type" property to be emitted as the first object in the dictionary:

{
  "$type": "System.Collections.Generic.Dictionary`2[[System.Guid, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]], mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089",
  "9648af76-7986-4b34-8b2c-97b2345769ef": "Test"
}

When deserializing using DeserializeObject, this token is normally consumed by Json.NET when the corresponding c# object is constructed. But you are using PopulateObject on a pre-allocated dictionary. Thus the metadata property is not consumed during construction and instead Json.NET tries to add it to the dictionary, and fails.

The solution is to set MetadataPropertyHandling = MetadataPropertyHandling.ReadAhead in deserializeSettings. Doing so will cause the "$type" property to be consumed or ignored (as appropriate) unconditionally:

var deserializeSettings = new JsonSerializerSettings
{
    TypeNameHandling = TypeNameHandling.All,
    TypeNameAssemblyFormat = FormatterAssemblyStyle.Full,
    Formatting = Formatting.Indented,
    MetadataPropertyHandling = MetadataPropertyHandling.ReadAhead
};
JsonConvert.PopulateObject(serializedObject, newDic, deserializeSettings);

Please note that, from the release notes, there is a slight cost in memory usage and speed from using this setting.

Alternatively, if you don't unconditionally need metadata type information in your JSON, you could serialize with TypeNameHandling = TypeNameHandling.Auto and only emit type information for polymorphic types, which your Dictionary<Guid, string> is not.

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