Deserialize collection of interface-instances?

Question

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<ITestInterface> collection?

Answer 1

I found this question while trying to do this myself. After I implemented Piotr Stapp's(Garath's) answer, I was struck by how simple it seemed. If I was merely implementing a method that was already being passed the exact Type (as a string) that I wanted to instantiate, why wasn't the library binding it automatically?

I actually found that I didn't need any custom binders, Json.Net was able to do exactly what I needed, provided I told it that was what I was doing.

When serializing:

string serializedJson = JsonConvert.SerializeObject(objectToSerialize, Formatting.Indented, new JsonSerializerSettings {     TypeNameHandling = TypeNameHandling.Objects,     TypeNameAssemblyFormat = System.Runtime.Serialization.Formatters.FormatterAssemblyStyle.Simple }); 

When de-serializing:

var deserializedObject = JsonConvert.DeserializeObject<ClassToSerializeViaJson>(serializedJson, new JsonSerializerSettings {     TypeNameHandling = TypeNameHandling.Objects }); 

Relevant documentation: Serialization Settings for Json.NET and TypeNameHandling setting

Answer 2

Bellow full working example with what you want to do:

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)     {         var resolvedTypeName = string.Format(TypeFormat, typeName);         return Type.GetType(resolvedTypeName, true);     } }  class Program {     static void Main()     {         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();     } }