title: Notifications when an ObservedObject is changed
body: <p>I have a graphical user interface made of several SwiftUI components (lets call them subviews).
  These subviews communicate with each other with the help of ObservableObject / ObservedObject.
  When changes are made to one view, the other view is automatically notified and updates itself.</p>
  <p>However, one of the subviews is not a SwiftUI view but a SpriteKit SKScene.
  Here, too, I would like to react to the changes in an observed value.
  But I do not have a view that updates automatically. I want to make adjustments to the sprites, depending on the observed value.</p>
  <p>How can I be notified of changes in the value?
  Can I call a method as soon as the value of the ObservedObject changes?</p>