protected override void MutateInternal()
 {
     if (mBlock != null)
     {
         UpdateInternal(mDropdown.GetValue().Equals(DIVISIBLE_BY));
     }
 }
        protected override void OnAttached()
        {
            mDropdown = mBlock.GetField("PROPERTY") as FieldDropdown;
            if (mDropdown == null)
            {
                throw new Exception("FieldDropDown \"PROPERTY\" not found.");
            }

            UpdateInternal(mDropdown.GetValue().Equals(DIVISIBLE_BY));

            //register observer
            mObserver = new MemorySafeMutatorObserver(this);
            mDropdown.AddObserver(mObserver);
        }