Thx you so much for fast answer @mvaneijgen and warm greetings on the forum )
Yes , I've already checked that case , but for it's implementation it need time to rework project for suiting this implementation (at least I think so).
Previous example was very easy for me due to easy section bounding .
If u think that my way is really tricky and Observer solution is easier , I'll try to implement it (those inners and outers confusing me).