Json.net自定义枚举转换器 [英] Json.net Custom enum converter
问题描述
我正在使用Json.net在我的应用程序中使用json。
我使用的API向我发送枚举的特定字符串格式,例如:
对于类型 TemperatureType
,值为 fahrenheit,Celcius
json值是:
{result:[TemperatureType_fahrenheit,TemperatureType_Celcius]}
我想使用转换器来直接管理它,以获得
$ IList< TemperatureType>
,但也适用于其他枚举类型。
有人有想法吗?
我尝试使用自定义JsonConverter:
if(reader.TokenType == JsonToken.String&& reader.Value!= null)
{
string value = reader。 Value.ToString();
var splitValues = value.Split('_');
if(splitValues.Length == 2)
{
var type = Type.GetType(splitValues [0]);
return Enum.Parse(type,splitValues [1]);
}
}
问题是GetType属性,因为我没有获取参数,指示所需的类型,没有命名空间
枚举类型是 objectType
参数 ReadJson
。但是,有几点:
- 您需要处理可空的枚举类型。
- 您需要处理
[Flag]
枚举。 Json.NET将这些值作为逗号分隔的值列表。 - 您需要处理具有无效值的枚举的情况。 Json.NET在
StringEnumConverter.AllowIntegerValues == true
时将数据写入数值,否则会引发异常。
这里是 StringEnumConverter
,通过调用基类来处理这些情况,然后在适当的时候添加或删除类型前缀:
pre $
public class TypePrefixEnumConverter:StringEnumConverter
{
public override object ReadJson(JsonReader reader,Type objectType,object existingValue,JsonSerializer serializer)
{
bool isNullable =(Nullable.GetUnderlyingType(objectType)!= null);
类型enumType =(Nullable.GetUnderlyingType(objectType)?objectType);
if(!enumType.IsEnum)
throw new JsonSerializationException(string.Format(type {0}不是枚举类型,enumType.FullName));
var prefix = enumType.Name +_;
if(reader.TokenType == JsonToken.Null)
{
if(!isNullable)
throw new JsonSerializationException();
返回null;
}
//从枚举组件中剥离前缀(如果有)。
var token = JToken.Load(reader);
if(token.Type == JTokenType.String)
{
token =(JValue)string.Join(,,token.ToString()Split(',')。选择(s => s.Trim())。选择(s => s.StartsWith(prefix)?s.Substring(prefix.Length):s).ToArray());
}
使用(var subReader = token.CreateReader())
{
while(subReader.TokenType == JsonToken.None)
subReader。读();
return base.ReadJson(subReader,objectType,existingValue,serializer); //使用基类转换
}
}
public override void WriteJson(JsonWriter writer,object value,JsonSerializer serializer)
{
var array = new JArray();
using(var tempWriter = array.CreateWriter())
base.WriteJson(tempWriter,value,serializer);
var token = array.Single();
if(token.Type == JTokenType.String&& value!= null)
{
var enumType = value.GetType();
var prefix = enumType.Name +_;
token =(JValue)string.Join(,,token.ToString()Split(',')选择(s => s.Trim())Select(s => !char.IsNumber(s [0])&& s [0]!=' - ')?prefix + s:s).ToArray());
}
token.WriteTo(writer);
}
}
然后,您可以使用它,无论何处可以使用< a href =http://www.newtonsoft.com/json/help/html/SerializeWithJsonConverters.htm =noreferrer> StringEnumConverter
,for实例:
var settings = new JsonSerializerSettings {Converters = new JsonConverter [] {new TypePrefixEnumConverter()}};
var json = JsonConvert.SerializeObject(myClass,Formatting.Indented,settings);
I'm currently using Json.net to consume json in my app. The API I use send me a specific string format for enum for example:
For an enum of type TemperatureType
with values fahrenheit, Celcius
The json value is:
{"result":["TemperatureType_fahrenheit","TemperatureType_Celcius"]}
I would like to use a converter to directly manage it to get
an IList<TemperatureType>
but also working for other enum types.
Does anybody have an idea ?
I've try to use a custom JsonConverter :
if (reader.TokenType == JsonToken.String && reader.Value != null)
{
string value = reader.Value.ToString();
var splitValues = value.Split('_');
if (splitValues.Length == 2)
{
var type = Type.GetType(splitValues[0]);
return Enum.Parse(type, splitValues[1]);
}
}
The problem is the GetType Property because I haven't got parameters indicating the desired type and no namespace
The enum type is the objectType
argument to ReadJson
. However, a few points:
- You need to handle nullable enum types.
- You need to handle
[Flag]
enumerations. Json.NET writes these as comma-separated lists of values. - You need to handle the case of an enum with an invalid value. Json.NET writes these as numeric values when
StringEnumConverter.AllowIntegerValues == true
and throws an exception otherwise.
Here is a subclass of StringEnumConverter
that handles these cases by calling the base class then adding or removing the type prefix when appropriate:
public class TypePrefixEnumConverter : StringEnumConverter
{
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
bool isNullable = (Nullable.GetUnderlyingType(objectType) != null);
Type enumType = (Nullable.GetUnderlyingType(objectType) ?? objectType);
if (!enumType.IsEnum)
throw new JsonSerializationException(string.Format("type {0} is not a enum type", enumType.FullName));
var prefix = enumType.Name + "_";
if (reader.TokenType == JsonToken.Null)
{
if (!isNullable)
throw new JsonSerializationException();
return null;
}
// Strip the prefix from the enum components (if any).
var token = JToken.Load(reader);
if (token.Type == JTokenType.String)
{
token = (JValue)string.Join(", ", token.ToString().Split(',').Select(s => s.Trim()).Select(s => s.StartsWith(prefix) ? s.Substring(prefix.Length) : s).ToArray());
}
using (var subReader = token.CreateReader())
{
while (subReader.TokenType == JsonToken.None)
subReader.Read();
return base.ReadJson(subReader, objectType, existingValue, serializer); // Use base class to convert
}
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var array = new JArray();
using (var tempWriter = array.CreateWriter())
base.WriteJson(tempWriter, value, serializer);
var token = array.Single();
if (token.Type == JTokenType.String && value != null)
{
var enumType = value.GetType();
var prefix = enumType.Name + "_";
token = (JValue)string.Join(", ", token.ToString().Split(',').Select(s => s.Trim()).Select(s => (!char.IsNumber(s[0]) && s[0] != '-') ? prefix + s : s).ToArray());
}
token.WriteTo(writer);
}
}
Then, you can use it wherever you could use StringEnumConverter
, for instance:
var settings = new JsonSerializerSettings { Converters = new JsonConverter[] { new TypePrefixEnumConverter() } };
var json = JsonConvert.SerializeObject(myClass, Formatting.Indented, settings);
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