json - 将多个值反序列化为单个属性

Question

我有一个包含一些标志的 JSON 响应:

{"df":1,"dr":0,"pf":0,"pr":0,"ft":0,"rt":1}

我想将其反序列化为标志枚举:

public class Foo {
    public Doors Doors { get; set; }
    public Trunk Trunks { get; set; }
}

df、dr、pf、pr 应该反序列化为 Doors 标志枚举，而 ft、rt 应该进入 Trunks。我希望这是做出决定的自定义代码。我正在寻找的是可以让我说的东西:

[JsonProperty("df,dr,pf,pr"), JsonConverter(typeof(DoorsConverter))]
public Doors Door { get; set; }

这将使我能够根据这些值来处理属性的构造。这种事情是否存在，或者我是否坚持将个人属性(property)插入非公共(public)领域并在事后构建属性(property)？

Answer 1

我同意@JeffMercado 的观点，处理这个问题的最佳方法是创建一个处理整个类的自定义转换器。您在评论中说您对创建这样的转换器感到困惑，因为您不想编写代码来处理所有其他类属性(未在您的问题中显示)，因为它们不需要任何特殊处理。为此，我提出了一个转换器的想法，它将使用 JSON.Net 的所有标准属性的常用机制序列化/反序列化您的对象，然后处理 Doors 和 Trunks 特别枚举字段。因为我不知道你的其他属性叫什么，所以我只是编了一些与汽车有关的属性。为了与该主题保持一致，我还将您的 Foo 类重命名为 Car。

下面是这个例子的类和枚举定义:

public class Car
{
    [JsonIgnore]
    public Door Doors { get; set; }
    [JsonIgnore]
    public Trunk Trunks { get; set; }
    [JsonProperty("make")]
    public string Make { get; set; }
    [JsonProperty("model")]
    public string Model { get; set; }
    [JsonProperty("year")]
    public int Year { get; set; }
    [JsonProperty("MSRP")]
    public decimal MSRP { get; set; }
}

[Flags]
public enum Door 
{
    None = 0,
    DriverSideFront = 1,
    DriverSideRear = 2,
    PassengerSideFront = 4,
    PassengerSideRear = 8 
}

[Flags]
public enum Trunk
{
    None = 0,
    Front = 1, 
    Rear = 2
}

这是自定义转换器的代码:

public class CarConverter : JsonConverter
{
    private static Dictionary<string, Door> doorMap;
    private static Dictionary<string, Trunk> trunkMap;

    static CarConverter()
    {
        doorMap = new Dictionary<string, Door>();
        doorMap.Add("df", Door.DriverSideFront);
        doorMap.Add("dr", Door.DriverSideRear);
        doorMap.Add("pf", Door.PassengerSideFront);
        doorMap.Add("pr", Door.PassengerSideRear);

        trunkMap = new Dictionary<string, Trunk>();
        trunkMap.Add("ft", Trunk.Front);
        trunkMap.Add("rt", Trunk.Rear);
    }

    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(Car));
    }

    public override object ReadJson(JsonReader reader, Type objectType, 
                                    object existingValue, JsonSerializer serializer)
    {
        JObject jo = JObject.Load(reader);
        Car car = jo.ToObject<Car>();
        car.Doors = GetDoors(jo);
        car.Trunks = GetTrunks(jo);
        return car;
    }

    private Door GetDoors(JObject obj)
    {
        Door doors = Door.None;
        foreach (KeyValuePair<string, Door> kvp in doorMap)
        {
            if (obj[kvp.Key].Value<int>() == 1)
            {
                doors |= kvp.Value;
            }
        }
        return doors;
    }

    private Trunk GetTrunks(JObject obj)
    {
        Trunk trunks = Trunk.None;
        foreach (KeyValuePair<string, Trunk> kvp in trunkMap)
        {
            if (obj[kvp.Key].Value<int>() == 1)
            {
                trunks |= kvp.Value;
            }
        }
        return trunks;
    }

    public override void WriteJson(JsonWriter writer, object value, 
                                   JsonSerializer serializer)
    {
        Car car = (Car)value;
        JObject obj = JObject.FromObject(value);
        AddDoors(obj, car.Doors);
        AddTrunks(obj, car.Trunks);
        obj.WriteTo(writer);
    }

    private void AddDoors(JObject obj, Door doors)
    {
        foreach (KeyValuePair<string, Door> kvp in doorMap)
        {
            obj.Add(kvp.Key, ((doors & kvp.Value) != Door.None) ? 1 : 0);
        }
    }

    private void AddTrunks(JObject obj, Trunk trunk)
    {
        foreach (KeyValuePair<string, Trunk> kvp in trunkMap)
        {
            obj.Add(kvp.Key, ((trunk & kvp.Value) != Trunk.None) ? 1 : 0);
        }
    }
}

最后，这是一个显示用法的测试程序:

static void Q18066528()
{
    string json = @"{""df"":1,""dr"":0,""pf"":0,""pr"":1,""ft"":0,""rt"":1,
       ""make"":""Chevrolet"",""model"":""Corvette"",""year"":2013,""MSRP"":49600}";

    JsonSerializerSettings settings = new JsonSerializerSettings 
    { 
        Converters = new List<JsonConverter> { new CarConverter() } 
    };

    Car car = JsonConvert.DeserializeObject<Car>(json, settings);

    Console.WriteLine("Model: " + car.Model);
    Console.WriteLine("Year: " + car.Year);
    Console.WriteLine("Doors: " + car.Doors);
    Console.WriteLine("Trunks: " + car.Trunks);

    string json2 = JsonConvert.SerializeObject(car, settings);

    Console.WriteLine(json2);
}

上面的输出:

Model: Corvette
Year: 2013
Doors: DriverSideFront, PassengerSideRear
Trunks: Rear
{"make":"Chevrolet","model":"Corvette","year":2013,"MSRP":49600.0,"df":1,"dr":0,
"pf":0,"pr":1,"ft":0,"rt":1}

重要提示:您可能想用 [JsonConverter(typeof(CarConverter))] 装饰 Car 类，但不要这样做。如果这样做，CarConverter 将无法正常工作:转换器最终将递归调用自身，直到出现 StackOverflowException 错误。 (手动处理所有类属性的转换器不会有这个问题。)