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JSON.net: how to deserialize without using the default constructor?

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天涯浪人
天涯浪人 2020-11-22 07:21

I have a class that has a default constructor and also an overloaded constructor that takes in a set of parameters. These parameters match to fields on the object and are a

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  • 粉色の甜心
    粉色の甜心 (楼主)
    2020-11-22 07:53

    A bit late and not exactly suited here, but I'm gonna add my solution here, because my question had been closed as a duplicate of this one, and because this solution is completely different.

    I needed a general way to instruct Json.NET to prefer the most specific constructor for a user defined struct type, so I can omit the JsonConstructor attributes which would add a dependency to the project where each such struct is defined.

    I've reverse engineered a bit and implemented a custom contract resolver where I've overridden the CreateObjectContract method to add my custom creation logic.

    public class CustomContractResolver : DefaultContractResolver {

    protected override JsonObjectContract CreateObjectContract(Type objectType)
    {
        var c = base.CreateObjectContract(objectType);
        if (!IsCustomStruct(objectType)) return c;

        IList list = objectType.GetConstructors(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic).OrderBy(e => e.GetParameters().Length).ToList();
        var mostSpecific = list.LastOrDefault();
        if (mostSpecific != null)
        {
            c.OverrideCreator = CreateParameterizedConstructor(mostSpecific);
            c.CreatorParameters.AddRange(CreateConstructorParameters(mostSpecific, c.Properties));
        }

        return c;
    }

    protected virtual bool IsCustomStruct(Type objectType)
    {
        return objectType.IsValueType && !objectType.IsPrimitive && !objectType.IsEnum && !objectType.Namespace.IsNullOrEmpty() && !objectType.Namespace.StartsWith("System.");
    }

    private ObjectConstructor CreateParameterizedConstructor(MethodBase method)
    {
        method.ThrowIfNull("method");
        var c = method as ConstructorInfo;
        if (c != null)
            return a => c.Invoke(a);
        return a => method.Invoke(null, a);
    }
}



    I'm using it like this.
    


    public struct Test {
  public readonly int A;
  public readonly string B;

  public Test(int a, string b) {
    A = a;
    B = b;
  }
}

var json = JsonConvert.SerializeObject(new Test(1, "Test"), new JsonSerializerSettings {
  ContractResolver = new CustomContractResolver()
});
var t = JsonConvert.DeserializeObject(json);
t.A.ShouldEqual(1);
t.B.ShouldEqual("Test");

    
    
    
             
    
                                                        
    
            
            
    
              
                
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