我有一个自定义类型:
[TypeConverter(typeof(FriendlyUrlTypeConverter))]
public class FriendlyUrl : IEquatable<FriendlyUrl>, IConvertible
{
public FriendlyUrl()
{
_friendlyUrl = string.Empty;
}
public FriendlyUrl(string value)
{
value = value.Trim();
if (!FriednlyUrlValidator.Validate(value))
throw new FriendlyUrlValidationException("Invalid value for FrienlyUrl");
_friendlyUrl = value;
}
public static implicit operator FriendlyUrl(string friendlyUrlValue)
{
if (friendlyUrlValue != "" && !FriednlyUrlValidator.Validate(friendlyUrlValue))
throw new FriendlyUrlValidationException($"Invalid value for FrienlyUrl: {friendlyUrlValue}");
return new FriendlyUrl { _friendlyUrl = friendlyUrlValue };
}
public static implicit operator string(FriendlyUrl furl)
{
return furl._friendlyUrl;
}
public override string ToString()
{
return _friendlyUrl;
}
private string _friendlyUrl;
//[...skip IEquatable implementation...]
TypeCode IConvertible.GetTypeCode()
{
return _friendlyUrl.GetTypeCode();
}
bool IConvertible.ToBoolean(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToBoolean(provider);
}
byte IConvertible.ToByte(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToByte(provider);
}
char IConvertible.ToChar(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToChar(provider);
}
DateTime IConvertible.ToDateTime(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToDateTime(provider);
}
decimal IConvertible.ToDecimal(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToDecimal(provider);
}
double IConvertible.ToDouble(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToDouble(provider);
}
short IConvertible.ToInt16(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToInt16(provider);
}
int IConvertible.ToInt32(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToInt32(provider);
}
long IConvertible.ToInt64(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToInt64(provider);
}
sbyte IConvertible.ToSByte(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToSByte(provider);
}
float IConvertible.ToSingle(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToSingle(provider);
}
string IConvertible.ToString(IFormatProvider provider)
{
return _friendlyUrl.ToString(provider);
}
object IConvertible.ToType(Type conversionType, IFormatProvider provider)
{
if (conversionType == typeof(FriendlyUrl))
return this;
return ((IConvertible) _friendlyUrl).ToType(conversionType, provider);
}
ushort IConvertible.ToUInt16(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToUInt16(provider);
}
uint IConvertible.ToUInt32(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToUInt32(provider);
}
ulong IConvertible.ToUInt64(IFormatProvider provider)
{
return ((IConvertible) _friendlyUrl).ToUInt64(provider);
}
}
这是Json序列化/反序列化(xUnit)的测试:
[Fact]
public void ConvertToJsonAndBack()
{
FriendlyUrl friendlyUrl = "some-friendly-url-1";
string friendlyUrlJson = JsonConvert.SerializeObject(friendlyUrl);
Assert.Equal($"\"{friendlyUrl}\"", friendlyUrlJson);
// ******** Throws the next line: ********
FriendlyUrl deserialized = JsonConvert.DeserializeObject<FriendlyUrl>(friendlyUrlJson);
Assert.Equal(friendlyUrl, deserialized);
}
它抛出以下异常:
Newtonsoft.Json.JsonSerializationException:将值“ some-friendly-url-1”转换为“ BlahBlah.Entities.FriendlyUrl”类型时出错。路径”,第1行,位置21。---- System.InvalidCastException:从'System.String'到'BlahBlah.Entities.FriendlyUrl'的无效转换。
堆栈跟踪:
堆栈跟踪:JsonSerializerInternalReader.EnsureType(JsonReader阅读器,对象值,CultureInfo文化,JsonContract合同,类型targetType)JsonSerializerInternalReader.CreateValueInternal(JsonReader阅读器,类型objectType,JsonContract合同,JsonProperty成员,JsonContainerContractContainerContracterInnerReader。 (JsonReader阅读器,类型objectType,布尔值checkAdditionalContent)JsonSerializer.DeserializeInternal(JsonReader阅读器,类型objectType)JsonSerializer.Deserialize(JsonReader阅读器,类型objectType)JsonConvert.DeserializeObject(字符串值,类型类型,JsonSerializerSettings []设置)[]字符串值,JsonSerializerSettings设置)JsonConvert.DeserializeObject [T](字符串值)
现在,如果我删除实现并仅保留它,它确实可以工作IConvertible
:
TypeConverter
实施-请参阅第一行。但是当类实现时,IConvertible
我得到了那个错误。我怎样才能解决这个问题?
(我确实需要IConvertible
实施。我也尝试使用JsonObject
它,但没有帮助)。
这是repro- https: //dotnetfiddle.net/YPfr60 。
public class FriendlyUrlTypeConverter : TypeConverter
{
public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
{
return sourceType == typeof(string) || base.CanConvertFrom(context, sourceType);
}
public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
{
return value is string sValue ? new FriendlyUrl(sValue) : base.ConvertFrom(context, culture, value);
}
public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
{
return destinationType == typeof(string) ? value.ToString() : base.ConvertTo(context, culture, value, destinationType);
}
}
因为您的类实现IConvertible
,所以JsonSerializerInternalReader
显然是在尝试调用,Convert.ChangeType
而不是使用TypeConverter
您提供的。源代码的第984行有一条注释,指出该注释Convert.ChangeType
不适用于custom IConvertible
,因此作者表面上意识到该问题:
if (contract.IsConvertable)
{
JsonPrimitiveContract primitiveContract = (JsonPrimitiveContract)contract;
...
// this won't work when converting to a custom IConvertible
return Convert.ChangeType(value, contract.NonNullableUnderlyingType, culture);
}
您可以通过JsonConverter
为FriendlyUrl
类实现自定义来解决此问题:
public class FriendlyUrlJsonConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return objectType == typeof(FriendlyUrl);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
return new FriendlyUrl((string)reader.Value);
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
writer.WriteValue(((FriendlyUrl)value).ToString());
}
}
要使用JsonConverter
,只需以[JsonConverter]
与您FriendlyUrl
相同的方式向类中添加一个属性[TypeConverter]
。然后[TypeConverter]
,您可以删除该属性,除非您出于其他目的需要它。(Json.Net在解析类型时会DefaultContractResolver
寻找JsonConverter
第一个,因此它将优先于TypeConverter
。)
[JsonConverter(typeof(FriendlyUrlJsonConverter))]
public class FriendlyUrl : IEquatable<FriendlyUrl>, IConvertible
{
...
}
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