我正在尝试进行 ajax 调用以从某个国家/地区获取状态,但我一直收到无效的强制转换异常。 我将 MVC4 与 json.NET 一起使用。 我可以在我的测试中毫无问题地序列化对象,但是当我进行 ajax 调用时,我不断收到错误。
这是值类型:
[JsonConverter(typeof(ValueObjectConverter))]
public class Code : IValueObject
{
private readonly string _code;
private Code(string code)
{
_code = code;
}
public override string ToString()
{
return _code;
}
public static implicit operator Code(string code)
{
return new Code(code);
}
public static implicit operator String(Code code)
{
return code.ToString();
}
}
这是我的对象:
public class CountryState : Entity
{
public Code CodeWPS { get; set; }
public Code CodeIAM { get; set; }
public Name Description { get; set; }
}
这是 jsonconverter:
public class ValueObjectConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(IValueObject));
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
return (IValueObject)existingValue;
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var item = (IValueObject)value;
writer.WriteValue(item.ToString());
writer.Flush();
}
}
这是 API 方法:
public IEnumerable<CountryState> GetStatesByCountry(string codeType, string countryCodeIam)
{
var states = _getAllCountriesQueryHandler.Handle(countryCodeIam);
return states;
}
这是我用 Firebug 得到的错误:
{"Message":"An error has occurred.","ExceptionMessage":"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.","ExceptionType":"System.InvalidOperationException","StackTrace":null,"InnerException":{"Message":"An error has occurred.","ExceptionMessage":"Error getting value from 'CodeWPS' on 'CNH.CSCN.BBS.Entities.CountryState'.","ExceptionType":"Newtonsoft.Json.JsonSerializationException","StackTrace":" at Newtonsoft.Json.Serialization.DynamicValueProvider.GetValue(Object target)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CalculatePropertyValues(JsonWriter writer, Object value, JsonContainerContract contract, JsonProperty member, JsonProperty property, JsonContract& memberContract, Object& memberValue)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)\r\n at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)\r\n at System.Net.Http.Formatting.JsonMediaTypeFormatter.<>c__DisplayClassd.<WriteToStreamAsync>b__c()\r\n at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action, CancellationToken token)","InnerException":{"Message":"An error has occurred.","ExceptionMessage":"Unable to cast object of type 'System.String' to type 'CNH.CSCN.BBS.Entities.ValueTypes.Code'.","ExceptionType":"System.InvalidCastException","StackTrace":" at GetCodeWPS(Object )\r\n at Newtonsoft.Json.Serialization.DynamicValueProvider.GetValue(Object target)"}}}
更新:
我添加了一个合约解析器:
public class SpecialContractResolver : DefaultContractResolver
{
protected override IValueProvider CreateMemberValueProvider(MemberInfo member)
{
if (member.MemberType == MemberTypes.Property)
{
var pi = (PropertyInfo)member;
if (typeof(IValueObject).IsAssignableFrom(pi.PropertyType))
{
return new IValueObjectValueProvider(member, pi.PropertyType);
}
}
else if (member.MemberType == MemberTypes.Field)
{
var fi = (FieldInfo)member;
if (typeof(IValueObject).IsAssignableFrom(fi.FieldType))
{
return new IValueObjectValueProvider(member, fi.FieldType);
}
}
return base.CreateMemberValueProvider(member);
}
}
和一个 IValueProvider:
public class IValueObjectValueProvider : IValueProvider
{
private readonly object _defaultValue;
private readonly IValueProvider _underlyingValueProvider;
public IValueObjectValueProvider(MemberInfo memberInfo, Type underlyingType)
{
_underlyingValueProvider = new DynamicValueProvider(memberInfo);
_defaultValue = underlyingType;
}
public void SetValue(object target, object value)
{
target = value;
}
public object GetValue(object target)
{
return target.ToString();
}
}
我知道我在正确的轨道上,我不再收到错误消息,但结果是:
对象 { CodeWPS="CNH.CSCN.BBS.Entities.CountryState", CodeIAM="CNH.CSCN.BBS.Entities.CountryState", Description="CNH.CSCN.BBS.Entities.CountryState"}
我认为我的 contractresolver 和 ivalueprovider 还不是 100% 正确...
最佳答案
是因为这段代码:
public override bool CanConvert(Type objectType)
{
return (objectType == typeof(IValueObject));
}
您的 objectType
不是 IValueObject
,它是 Code
- 所以 CanConvert
返回 false
并且您的转换器未被使用。您的代码应如下所示:
return typeof(IValueObject).IsAssignableFrom(objectType);
在这个条件下,实现类也匹配。
关于c# - 使用 json.net 序列化值类型,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/18145251/