c# - 在 JSON.NET 中反序列化十进制值的自定义规则

Question

当我使用JsonConvert.DeserializeObject将JSON数据转换为自定义类时遇到问题，只要null属性值需要decimal.

我想实现一个自定义规则，该规则仅在我想要时使用——不想要全局设置。在这种特殊情况下，我希望只要属性是十进制类型，null值就会变为。0

我该如何做到这一点？

标签： c#jsonjson.net

Answer 1

您可以在要反序列化的类型中使用注释，也可以在反序列化时指定自定义转换器/设置（而不是全局）。我认为，仅处理某些 属性的唯一好方法decimal是使用注释。

string json = @"{""val"": null}";

public class NoAnnotation {
    public decimal val {get; set;}
}

public class WithAnnotation {
    [JsonConverter(typeof(CustomDecimalNullConverter))]
    public decimal val {get; set;}
}

void Main()
{   
    // Converting a type that specifies the converter
    // with attributes works without additional setup
    JsonConvert.DeserializeObject(json, typeof(WithAnnotation));

    // Converting a POCO doesn't work without some sort of setup,
    // this would throw
    // JsonConvert.DeserializeObject(json, typeof(NoAnnotation));

    // You can specify which extra converters
    // to use for this specific operation.
    // Here, the converter will be used
    // for all decimal properties
    JsonConvert.DeserializeObject(json, typeof(NoAnnotation),
       new CustomDecimalNullConverter());

    // You can also create custom serializer settings.
    // This is a good idea if you need to serialize/deserialize multiple places in your application,
    // now you only have one place to configure additional converters
    var settings = new JsonSerializerSettings();
    settings.Converters.Add(new CustomDecimalNullConverter());
    JsonConvert.DeserializeObject(json, typeof(NoAnnotation), settings);
}

// For completeness: A stupid example converter
class CustomDecimalNullConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(decimal);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        if (reader.TokenType == JsonToken.Null)
        {
            return 0m;
        }
        else
        {
            return Convert.ToDecimal(reader.Value);
        }
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        writer.WriteValue((decimal)value);
    }
}