构建一个JsonConstructor来反序列化我的对象

Question

我正在使用JSON.net，我试图从开源UnitClassLibrary序列化和反序列化一个距离对象。目前，我有一个对象序列化为以下JSON:

{
    "ThirtySecondsOfAnInch": 454,
    "SixteenthsOfAnInch": 227,
    "EighthsOfAnInch": 113.5,
    "QuartersOfAnInch": 56.75,
    "HalvesOfAnInch": 28.375,
    "Inches": 14.1875,
    "Feet": 1.1822916666666667,
    "Yards": 0.3940972222222222,
    "Miles": 0.00022391887626262627,
    "Millimeters": 360.36249999999995,
    "Centimeters": 36.03625,
    "Meters": 0.3603625,
    "Kilometers": 0.0003603625,
    "Architectural": "1'2 3/16""
}

我可以取其中任何一个，并使用这个类将其转换为距离对象。例如，对于最后一个体系结构字符串，我可以使用以下构造函数:

Distance newDistance = new Distance("1'2 3/16"");

或者，使用32英寸，我可以这样做:

Distance newDistance = new Distance(DistanceType.ThirtySecond, 454.0);

然而，我不确定编写JsonConstructor (JSON.net可以专门使用的构造函数类型)的最佳方法是在传递带有JsonConvert.DeserializeObject<Distance>(json);的JSON字符串时接受任何一种类型的输出。

我如何写一个构造函数来接受一个新的距离对象?

Answer 1

下面是一个JsonConverter示例。

public class DistanceConverter : JsonConverter
{
    private readonly IDictionary<string, DistanceType> _distanceTypeMap;
    public DistanceConverter()
    {
        _distanceTypeMap = new Dictionary<string, DistanceType>
        {
            {"Meters", DistanceType.Meter},
            {"Yards", DistanceType.Yard}
        };
    }
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        Distance distance = value as Distance;
        if (distance == null)
        {
            writer.WriteNull();
            return;
        }
        writer.WriteStartObject();
        foreach (KeyValuePair<string, DistanceType> pair in _distanceTypeMap)
        {
            writer.WritePropertyName(pair.Key);
            writer.WriteValue(distance.GetValue(pair.Value));
        }
        writer.WriteEndObject();
    }
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        Distance result = null;
        while (reader.Read())
        {
            var key = reader.Value;
            string value = reader.ReadAsString();
            if (result == null && key != null)
            {
                DistanceType distanceType;
                if (_distanceTypeMap.TryGetValue(key.ToString(), out distanceType))
                {
                    double parsedValue = JToken.Parse(value).Value<double>();
                    result = new Distance(distanceType, parsedValue);
                }
            }
        }
        return result;
    }
    public override bool CanConvert(Type objectType)
    {
        return typeof(Distance) == objectType;
    }
}

这个目前有问题。我不明白为什么即使我在反序列化中创建对象，也会得到零距离。下面是查看结果的几个测试:

更新:我在再次阅读时修复了错误。它目前可以工作，但当你向字典中添加其他单位时，可能会出现异常。

public class DistanceConverterTests
{
    private JsonSerializerSettings _jsonSerializerSettings;
    [SetUp]
    public void Setup()
    {
        _jsonSerializerSettings = new JsonSerializerSettings
        {
            Converters = new List<JsonConverter> { new DistanceConverter() }
        };
    }

    [Test]
    public void DeserializeTest()
    {
        string json = File.ReadAllText("data.json");
        var distance = JsonConvert.DeserializeObject<Distance>(json, _jsonSerializerSettings);
        distance.Meters.Should().BeInRange(0.360, 0.361);
    }
    [Test]
    public void SerializeTest()
    {
        Distance distance = new Distance(DistanceType.Meter, 2.20);
        string json = JsonConvert.SerializeObject(distance, _jsonSerializerSettings);
        Console.WriteLine(json);
    }
}