Add/Remove TypeInfoResolver to existing JsonSerializerOptions

Starting with .NET 8, the JsonSerializerOptions class features a new TypeInfoResolverChain property in addition to the existing TypeInfoResolver property. With this new property, you are no longer required to specify all the resolvers in the same place, instead, you can add them later as needed.

Let’s look at an example:

var options = new JsonSerializerOptions
{
    TypeInfoResolver = JsonTypeInfoResolver.Combine(
        new ResolverA(), 
        new ResolverB()
    );
};

options.TypeInfoResolverChain.Add(new ResolverC());
Code language: C# (cs)

Besides adding new type resolvers to an existing JsonSerializerOptions, TypeInfoResolverChain also allows you to remove type info resolvers from the serializer options.

options.TypeInfoResolverChain.RemoveAt(0);Code language: C# (cs)

If you want to prevent changes to the type info resolver chain, you can do it by making the JsonSerializerOptions instance read-only. That is done by calling the MakeReadOnly() method on the options instance and will force the following InvalidOperationException in case anyone attempts to modify the type info resolver chain after the fact.

Unhandled exception. System.InvalidOperationException: This JsonSerializerOptions instance is read-only or has already been used in serialization or deserialization.
   at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_SerializerOptionsReadOnly(JsonSerializerContext context)
   at System.Text.Json.JsonSerializerOptions.VerifyMutable()
   at System.Text.Json.JsonSerializerOptions.OptionsBoundJsonTypeInfoResolverChain.OnCollectionModifying()
   at System.Text.Json.Serialization.ConfigurationList`1.Add(TItem item)Code language: plaintext (plaintext)