user1130329 user1130329 - 6 days ago 6
C# Question

JSON.NET - how to deserialize collection of interface-instances?

i would like to serialize this code via json.net:

public interface ITestInterface
{
string Guid {get;set;}
}

public class TestClassThatImplementsTestInterface1
{
public string Guid { get;set; }
}

public class TestClassThatImplementsTestInterface2
{
public string Guid { get;set; }
}


public class ClassToSerializeViaJson
{
public ClassToSerializeViaJson()
{
this.CollectionToSerialize = new List<ITestInterface>();
this.CollectionToSerialize.add( new TestClassThatImplementsTestInterface2() );
this.CollectionToSerialize.add( new TestClassThatImplementsTestInterface2() );
}
List<ITestInterface> CollectionToSerialize { get;set; }
}


I want to serialize/deserialize ClassToSerializeViaJson with json.net. Serialization is working, but deserialization gives me this error:

Newtonsoft.Json.JsonSerializationException: Could not create an instance of type ITestInterface. Type is an interface or abstract class and cannot be instantiated.

So how can I deserialize the List collection?

Thanks

Answer

Bellow full working example with what you want to do:

namespace ConsoleApplication
{

    public interface ITestInterface
    {
        string Guid { get; set; }
    }

    public class TestClassThatImplementsTestInterface1 : ITestInterface
    {
        public string Guid { get; set; }
        public string Something1 { get; set; }
    }

    public class TestClassThatImplementsTestInterface2 : ITestInterface
    {
        public string Guid { get; set; }
        public string Something2 { get; set; }
    }


    public class ClassToSerializeViaJson
    {
        public ClassToSerializeViaJson()
        {
            this.CollectionToSerialize = new List<ITestInterface>();
        }
        public List<ITestInterface> CollectionToSerialize { get; set; }
    }

    public class TypeNameSerializationBinder : SerializationBinder
    {
        public string TypeFormat { get; private set; }

        public TypeNameSerializationBinder(string typeFormat)
        {
            TypeFormat = typeFormat;
        }

        public override void BindToName(Type serializedType, out string assemblyName, out string typeName)
        {
            assemblyName = null;
            typeName = serializedType.Name;
        }

        public override Type BindToType(string assemblyName, string typeName)
        {
            string resolvedTypeName = string.Format(TypeFormat, typeName);

            return Type.GetType(resolvedTypeName, true);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            var binder = new TypeNameSerializationBinder("ConsoleApplication.{0}, ConsoleApplication");
            var toserialize = new ClassToSerializeViaJson();
            toserialize.CollectionToSerialize.Add(new TestClassThatImplementsTestInterface1() { Guid = Guid.NewGuid().ToString(), Something1 = "Some1" });
            toserialize.CollectionToSerialize.Add(new TestClassThatImplementsTestInterface2() { Guid = Guid.NewGuid().ToString(), Something2 = "Some2" });

            string json = JsonConvert.SerializeObject(toserialize, Formatting.Indented, new JsonSerializerSettings
            {
                TypeNameHandling = TypeNameHandling.Auto,
                Binder = binder
            });
            var obj = JsonConvert.DeserializeObject < ClassToSerializeViaJson>(json, new JsonSerializerSettings
                {
                    TypeNameHandling = TypeNameHandling.Auto,
                    Binder = binder 
                });
            Console.ReadLine();

        }
    }
}
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