JSON.NET deserializing derived classes does not work as expected - json

Question

I have been searching the forums and the JSON.NET website on this issue and from what I can see I'm correctly following the guidelines but it is not working correctly.
I'm trying to deserialize object from derived classes.
Serializing works fine, but when deserializing it tries to deserialize in to the wrong type.
I'm trying to do this with Windows Phone 8 and JSON.NET 4.5.11
I have the following classes which I am serializing:
public class MyClass : ModelBase
{
public string Title { get; set; }
[JsonProperty(TypeNameHandling = TypeNameHandling.All)]
public MyAction Action {get; set; }
}
public abstract class MyAction : ModelBase
{
[JsonIgnore()]
public abstract ActionType ActionType { get; }
public abstract void Execute();
}
public class SettingsAction : MyAction
{
public override ActionType ActionType
{
get { return ActionType.Settings; }
}
public SettingsType SettingsType {get; set; }
public override void Execute()
{
}
}
public class NoneAction : MyAction
{
public override ActionType ActionType
{
get { return ActionType.None; }
}
public override void Execute()
{
return;
}
}
I serialize it like this:
MyClass obj = new MyClass
{
Action = new SettingsAction()
};
string json = JsonConvert.SerializeObject(
obj,
Formatting.Indented,
new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.All });
using (StreamWriter writer = new StreamWriter(stream))
{
writer.Write(json);
}
And it gives me the following JSON:
{
"$type": "Model.MyClass, Model",
"Title": null,
"Action": {
"$type": "Model.SettingsAction, Model",
"SettingsType": 0
}
}
As far as I can see, this is correct, I told it to include the type information and it's correctly included.
The I deserialize it like this:
using (StreamReader r = new StreamReader(stream))
{
string json = r.ReadToEnd();
MyClass obj = JsonConvert.DeserializeObject<MyClass>(json);
}
And I get the following error:
JsonSerializationException: Error setting value to 'SettingsType' on 'Model.NoneAction'
So, although the type is contained in the JSON, on serializing it's ignoring it and of course deserializing it into a different type fails.
Does anyone have an idea why it's not taking the information into account and deserialize to the correct type?

Answer 1

I have found the culprit:
In one of my properties I was doing this:
public MyAction Action
{
get
{
if (_Action == null) {
Action = new NoneAction();
}
return _Action;
}
set
{
if (value != _Action)
{
_Action = value;
NotifyPropertyChanged("Action");
}
}
}
The problem is in the getter, where I create a NoneAction if the obejct is null.
Apparently Json.NET calls into the getter at some point between creating the MyClass object and setting the values of the MyAction object. When it sees that the Action-property is not null, it tries to assign the values instead of overwrite the whole object.