Animation<double> parent

The animation whose value this animation will proxy.

This value is mutable. When mutated, the listeners on the proxy animation will be transparently updated to be listening to the new parent animation.

Source 

Animation<double> get parent => _parent;
void parent=(Animation<double> value)

Source 

set parent(Animation<double> value) {
  if (value == _parent)
    return;
  if (_parent != null) {
    _status = _parent.status;
    _value = _parent.value;
    if (isListening)
      didStopListening();
  }
  _parent = value;
  if (_parent != null) {
    if (isListening)
      didStartListening();
    if (_value != _parent.value)
      notifyListeners();
    if (_status != _parent.status)
      notifyStatusListeners(_parent.status);
    _status = null;
    _value = null;
  }
}