detach method
override
    Mark this render object as detached from its PipelineOwner.
Typically called only from the parent's detach, and by the owner to mark the root of a tree as detached.
Subclasses with children should override this method to
detach all their children after calling the inherited method,
as in super.detach().
Implementation
@override
void detach() {
  // It's possible that the renderObject be detached during mouse events
  // dispatching, set the [MouseTrackerAnnotation.validForMouseTracker] false to prevent
  // the callbacks from being called.
  _validForMouseTracker = false;
  super.detach();
}