InvalidCastException occurs when a subclass obtains the Formatter of the base class.

[Liangjia0411]

When the base class defines a Formatter through JsonCustomSerializerAttribute, the subclass may obtain the Formatter when it obtains the Formatter; but when the code runs to ResolverBase.cs Line147, an InvalidCastException will occur.
In order to solve this problem, when performing BuildFormatter, "type. GetCustomAttribute()" should not consider inheriting?

[Tornhoof]

I'm not sure I follow, can you please provide a repro for this?

[Liangjia0411]

This is my test code. When I try to serialize an object of type ClassB, the following error will appear: "InvalidCastException: Unable to cast object of type 'MyTest.ClassAFormatter' to type 'SpanJson.IJsonFormatter2[MyTest.ClassB" ,System.Char]`'.
"

using SpanJson;

namespace MyTest
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var b = new ClassB { A = 1 };

            var jsonB = JsonSerializer.Generic.Utf16.Serialize(b);
        }
    }

    [JsonCustomSerializer(typeof(ClassAFormatter))]
    public class ClassA
    {
        public int A { get; set; }
    }

    public class ClassB : ClassA
    {
    }

    public class ClassAFormatter : ICustomJsonFormatter<ClassA>
    {
        public object Arguments { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }

        public static ClassAFormatter Default = new ClassAFormatter();

        public void Serialize(ref JsonWriter<char> writer, ClassA value)
        {
            throw new NotImplementedException();
        }

        public void Serialize(ref JsonWriter<byte> writer, ClassA value)
        {
            throw new NotImplementedException();
        }

        public ClassA Deserialize(ref JsonReader<byte> reader)
        {
            throw new NotImplementedException();
        }

        public ClassA Deserialize(ref JsonReader<char> reader)
        {
            throw new NotImplementedException();
        }

    }

}

[Tornhoof]

Yeah, I don't think that inheritance works with custom serializers, the concept is not really designed for that.