在json中将类的字节数组属性序列化为布尔值

Question

I have the following class

public class MyClass
{
     public int Id { get; set; }           
     public byte[] Logo { get; set; }   
}

I want to serialize Logo property in json as boolean: true if Logo is different than null, false otherwise. How can I use JsonProperty decorator?

Answer 1

If you use the following JsonConverter class, it will serialize how you want. I haven't implemented ReadJson (deserialization), since the data is no longer there. There are other ways to implement this, I'm sure, but I simply serialized an anonymous object with the right data. At first, I tried to write a converter for byte[] , but Json.NET apparently doesn't even try to use the converter for null values, so it'd give null or true , instead of false or true .

public class MyClassConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return typeof(MyClass) == objectType;
    }
    public override object ReadJson(JsonReader reader, Type objectType,
                 object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
    public override void WriteJson(JsonWriter writer, object value,
                                     JsonSerializer serializer)
    {
        var myClass = (MyClass)value;
        serializer.Serialize(writer, new { Id = myClass.Id,
                                           Logo = myClass.Logo != null });
    }
}

Either specify it as the converter for the class:

[JsonConverter(typeof(MyClassConverter))]
public class MyClass
{
    public int Id { get; set; }
    public byte[] Logo { get; set; }
}

Or specify it when you're serializing (I'd recommend this if you can't modify MyClass , or only sometimes want to serialize it like this):

var s1 = JsonConvert.SerializeObject(new MyClass(), new MyClassConverter());
var s2 = JsonConvert.SerializeObject(new MyClass
        { Id = 1, Logo = new byte[] { 1, 2, 3, } }, new MyClassConverter());

---

Here's another way to do it. I'd prefer this if you're ok with adding a property and able to modify MyClass :

public class MyClass
{
     public int Id { get; set; }
     [JsonProperty("Logo")]
     public bool HasLogo { get { return Logo != null; } }
     [JsonIgnore]
     public byte[] Logo { get; set; }
}

Outputs something like:

{"Id":0,"Logo":false} // or
{"Id":1,"Logo":true}