Serializable Type

gistfile1.txt

[Serializable]
public class SerializedType : ISerializationCallbackReceiver
{
    [SerializeField]
    public string serializedTypeName = "";
    [NonSerialized]
    public Type type = null;

    public SerializedType(System.Type t)
    {
        type = t;
    }

    public void OnBeforeSerialize()
    {
        if (type != null)
        {
            serializedTypeName = type.AssemblyQualifiedName;
        }
    }

    public void OnAfterDeserialize()
    {
        type = Type.GetType(serializedTypeName);
    }
}

Serializable Type Drawer Example

  [TypeSelect(typeof(Component))]
  public SerializedType componentType;

Type Select Attribute

  [AttributeUsage(AttributeTargets.Field)]
  public class TypeSelect : PropertyAttribute
  {
      public readonly Type selectTypesOf;
      public TypeSelect(Type t)
      {
          selectTypesOf = t;
      }
  }

Type Select Drawer

[CustomPropertyDrawer(typeof(TypeSelect))]
public class SpecialTypeDrawer : PropertyDrawer
{
    private SerializedProperty typeField;
    private DropdownField dropdown;

    public override VisualElement CreatePropertyGUI(SerializedProperty property)
    {
        VisualElement ve = new VisualElement();
        typeField = property.FindPropertyRelative(nameof(SerializedType.serializedTypeName));

        if (typeField == null)
            return null;

        var typeSelectAttr = this.attribute as TypeSelect;
        var types = TypeCache.GetTypesDerivedFrom(typeSelectAttr.selectTypesOf);
        if(typeField == null)
            Debug.Log("Null!");

        List<string> things = new List<string>(types.Count);
        foreach (var type in types)
        {
            things.Add(type.Name);
        }

        dropdown = new DropdownField(ObjectNames.NicifyVariableName(fieldInfo.Name), 
            things, 1);
        dropdown.SetValueWithoutNotify(typeField.stringValue);
        ve.Add(dropdown);

        return ve;
    }