这可以应用于几个问题，其中列表包含有限数量的项目，如城市，货币，语言等列表。
我正在尝试找到一种方法将类序列化为其Id，然后反序列化回其完整描述。例如，如果我们有这样的城市结构：
public struct City
{
public string Name;
public Country Country;
}
[JsonObject(MemberSerialization.OptIn)]
public class Country
{
public Country(string code, string name) { Code = code; Name = name; }
[JsonProperty]
public string Code;
public string Name;
}
public class Countries
{
public static List<Country> All = new List<Country>()
{
new Country("US", "United States"),
new Country("GB", "United Kingdom"),
new Country("FR", "France"),
new Country("ES", "Spain"),
};
}
我不介意国家序列化为{＆＃34;代码＆＃34;：＆＃34; ES＆＃34;}或简单地＆＃34; ES＆＃34;，但我希望它被反序列化为Countries.All中的现有国家实例
我怎么能得到这种行为？
答案 0 :(得分：2)
您有两种解决方案：
我很快就会有例子，我需要先输入em。 编辑：示例已完成
在这两种情况下
在这两个示例中，我使用JsonConvertAttribute来设置在序列化或反序列化对象时应使用哪个转换器。此参数告诉json.net库默认情况下序列化对象/参数时要使用的类/转换器。
如果您只需要在特定时刻进行序列化，则必须选择2种不同的方案：
将国家/地区保留为对象/结构
在我看来，这个选项是2个解决方案中最灵活和最实用的选项，因为它允许更改需求和减少异常抛出。
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace MyApplication
{
public struct City
{
public string Name;
// you could also set a converter for this field specifically if you only need for specific fields but also
// still want it to display as a normal json object when you serialise the object.
// [JsonConverter(typeof(CountryConverter))]
public Country Country;
}
// Setting a json converter attribute allows json.net to understand that an object by default
// will be serialised and deserialised using the specified converter.
[JsonConverter(typeof(CountryConverter))]
public class Country
{
public Country(string code)
{
switch (code)
{
case "US": Name = "United-States"; break;
case "GB": Name = "United Kingdom"; break;
case "FR": Name = "France"; break;
case "ES": Name = "Spain"; break;
case "CA": Name = "Canada"; break;
}
}
public string Code { get; set; }
public string Name { get; set; }
}
public class CountryConverter : JsonConverter<Country>
{
// Assuming that the countries are serialised using the code
public override Country ReadJson(JsonReader reader, Type objectType, Country existingValue, bool hasExistingValue, JsonSerializer serializer)
{
if(reader.Value == null && reader.ValueType == typeof(string))
{
return null;
}
string code = (string) reader.Value;
code = code.ToUpperInvariant(); // Because reducing error points is usually a good thing
return new Country(code);
}
public override void WriteJson(JsonWriter writer, Country value, JsonSerializer serializer)
{
//Writes the code as the value for the object
writer.WriteValue(value.Code);
}
}
}
将国家/地区更改为枚举
使用枚举可能很棒，因为它允许您拥有一组不变的值，而不必一遍又一遍地创建新对象。但它会使你的转换逻辑变得更复杂。
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace MyApplication
{
public struct City
{
public string Name;
public Country Country;
}
// Using the full name as it makes it easier to work with and also because you'd need a json converter
// if you want a string and not the number/index of the country when you serialise the data
[JsonConverter(typeof(CountryConverter))]
public enum Country
{
UnitedStates,
UnitedKingdom,
France,
Spain,
Canada
}
// this class only exists for you to add extentions to this enums.
// In short extentions are a type of methods added to other classes that act
// as if they were part of outher classes. usually this means that the first parameter
// is prefixed by this.
public static class CountryExtentions
{
public static string GetCode(this Country country)
{
switch (country)
{
case Country.UnitedStates: return "US";
case Country.UnitedKingdom: return "GB";
case Country.France: return "FR";
case Country.Spain: return "SP";
case Country.Canada: return "CA";
default: throw new InvalidOperationException($"This country has no code {country.ToString()}");
}
}
}
public class CountryConverter : JsonConverter<Country>
{
// Assuming that the countries are serialised using the code
public override Country ReadJson(JsonReader reader, Type objectType, Country existingValue, bool hasExistingValue, JsonSerializer serializer)
{
// make sure you can convert the thing into a string
if (reader.Value == null && reader.ValueType == typeof(string))
{
throw new InvalidOperationException($"The data type passed {reader.ValueType.Name} isn't convertible. The data type musts be a string.");
}
// get the value
string code = (string)reader.Value;
code = code.ToUpperInvariant(); // Because reducing error points is usually a good thing
// cycle through the enum values to compare them to the code
foreach (Country country in Enum.GetValues(typeof(Country)))
{
// if the code matches
if (country.GetCode() == code)
{
// return the country enum
return country;
}
}
// if no match is found, the code is invlalid
throw new InvalidCastException("The provided code could not be converted.");
}
public override void WriteJson(JsonWriter writer, Country value, JsonSerializer serializer)
{
//Writes the code as the value for the object
writer.WriteValue(value.GetCode());
}
}
}
答案 1 :(得分：1)
我建议使用JsonConverter，如此：
public class CountryConverter : JsonConverter
{
public override bool CanRead { get { return true; } }
public override bool CanWrite { get { return false; } }
public override bool CanConvert(Type objectType)
{
return typeof(Country) == objectType;
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
var obj = JObject.Load(reader);
var code = obj.GetValue("code", StringComparison.OrdinalIgnoreCase)?.Value<string>();
if (code != null)
{
return Countries.All.FirstOrDefault(c => string.Equals(c.Code, code, StringComparison.OrdinalIgnoreCase));
}
return null;
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
throw new NotImplementedException();
}
}
它不负责序列化对象，只对其进行反序列化。要反序列化它们，它会读取＆＃34;代码＆＃34;字段，然后从Countries.All列表返回第一个匹配的国家/地区。使用字典可能是最好的（更有效率）。
要使用此功能，只需装饰您的国家/地区类：
[JsonConverter(typeof(CountryConverter))]
public class Country