【C#】リフレクションを利用してArrayやIListにデータを追加する

        public static void AddListByReflection(this FieldInfo fieldInfo, object obj)
        {
            var elementType = fieldInfo.FieldType.GetArrayType();
            if (elementType == null)
                return;

            var instance = Activator.CreateInstance(elementType);
            if (fieldInfo.FieldType.IsArray)
            {
                var array = fieldInfo.GetValue(obj) as Array;
                var newArray = Array.CreateInstance(elementType, array.Length + 1);
                for (var i = 0; i < array.Length; i++)
                {
                    newArray.SetValue(array.GetValue(i), i);
                }
                newArray.SetValue(instance, array.Length);
                fieldInfo.SetValue(obj, newArray);
            }
            else if (fieldInfo.FieldType.IsGenericType && fieldInfo.FieldType.GetGenericTypeDefinition() == typeof(List<>))
            {
                var list = fieldInfo.GetValue(obj) as IList;
                list.Add(instance);
            }
        }

        private static Type GetArrayType(this Type type)
        {
            if (type.IsArray)
                return type.GetElementType();
 
            if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(List<>))
                return type.GetGenericArguments()[0];

            return null;
        }