使用 Json.Net 自定义日期时间序列化

Question

我试图创建自定义日期时间转换器失败。问题：我有很多对象要序列化，其中一些包含 DateTime 的包含 DateTime.MinValue 的属性。我想将其序列化为空。但是我要求在对象内部装饰适当的所有解决方案（我不能这样做）我在下面找到的其他解决方案是创建转换器，据我所知，该转换器仅适用于显式返回的 DateTime 对象而不是在其他对象内部。请帮忙。

public class DateTimeConverter : JsonConverter
{
    private readonly Type[] types;

    public DateTimeConverter(params Type[] types)
    {
        this.types = types;
    }

    public override bool CanConvert(Type objectType)
    {
        return types.Any(t => t == objectType);
    }
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        JToken t = JToken.FromObject(value);

        if (t.Type != JTokenType.Object)
        {
            if (value is DateTime && value.Equals(DateTime.MinValue))
            {
                t = JToken.FromObject(null);
                t.WriteTo(writer);
            }
            else
            {
                t.WriteTo(writer);
            }
        }
        else
        {
            if (value.Equals(DateTime.MinValue)) {
                t = JToken.FromObject(null);
                t.WriteTo(writer);
            }
            else {
                t.WriteTo(writer);
            }
        }
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException("Unnecessary because CanRead is false. The type will skip the converter.");
    }

Answer 1

我认为你把事情复杂化了。您的转换器应该只关心转换日期值，而不是可能包含日期值的对象。每当在任何其他对象中遇到日期时，序列化程序都会自然地调用您的转换器。

这是一个简单的转换器，可以满足您的需求：

public class MinDateToNullConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        // This converter handles date values directly
        return (objectType == typeof(DateTime));
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        // The CanConvert method guarantees the value will be a DateTime
        DateTime date = (DateTime)value;
        if (date == DateTime.MinValue)
        {
            writer.WriteNull();
        }
        else
        {
            writer.WriteValue(date);
        }
    }

    public override bool CanRead
    {
        get { return false; }
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

这是一个演示，显示转换器在对象的嵌套层次结构中处理日期：

class Program
{
    static void Main(string[] args)
    {
        Example example = new Example
        {
            Date1 = new DateTime(2014, 2, 2),
            Date2 = DateTime.MinValue,
            Inner = new Inner
            {
                DateA = DateTime.MinValue,
                DateB = new DateTime(1954, 1, 26)
            },
            MoreDates = new List<DateTime>
            {
                new DateTime(1971, 11, 15),
                DateTime.MinValue
            }
        };

        // Set up the serializer to use our date converter
        JsonSerializerSettings settings = new JsonSerializerSettings();
        settings.Converters.Add(new MinDateToNullConverter());
        settings.Formatting = Formatting.Indented;

        string json = JsonConvert.SerializeObject(example, settings);
        Console.WriteLine(json);
    }
}

class Example
{
    public DateTime Date1 { get; set; }
    public DateTime Date2 { get; set; }
    public Inner Inner { get; set; }
    public List<DateTime> MoreDates { get; set; }
}

class Inner
{
    public DateTime DateA { get; set; }
    public DateTime DateB { get; set; }
}

输出：

{
  "Date1": "2014-02-02T00:00:00",
  "Date2": null,
  "Inner": {
    "DateA": null,
    "DateB": "1954-01-26T00:00:00"
  },
  "MoreDates": [
    "1971-11-15T00:00:00",
    null
  ]
}