How to Serialize and Deserialize Derived Types in C# with Json.net?

Serialize and deserialize derived types using Json.net

Json.net (Newtonsoft) requires special handling to properly serialize and deserialize derived types when using polymorphic inheritance in C#. This article explores how to do this by enabling type name handling.

Question

Consider the following class hierarchy:

public class Base
{
    public string Name;
}
public class Derived : Base
{
    public string Something;
}

Now, if you try to deserialize a JSON string containing a list of Base objects, but it actually contains Derived objects, you will not be able to recover the derived type information. How to solve this problem?

Answer

Json.net provides the TypeNameHandling option, which enables serialization and deserialization of type names. To use this feature:

1. Create a JsonSerializerSettings object and set TypeNameHandling to TypeNameHandling.All.
2. Pass this settings object as a parameter to the SerializeObject and DeserializeObject methods.

Here is an example:

// 序列化
Base object1 = new Base() { Name = "Object1" };
Derived object2 = new Derived() { Something = "Some other thing" };
List<Base> inheritanceList = new List<Base>() { object1, object2 };

JsonSerializerSettings settings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.All };
string Serialized = JsonConvert.SerializeObject(inheritanceList, settings);

// 反序列化
List<Base> deserializedList = JsonConvert.DeserializeObject<List<Base>>(Serialized, settings);

This approach ensures that Json.net preserves type information during serialization and restores it during deserialization, allowing derived types to be restored correctly.

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