removeAll method
Remove all their children from this render object's child list.
More efficient than removing them individually.
Implementation
@override
void removeAll() {
  super.removeAll();
  _paintingOrder = null;
}Remove all their children from this render object's child list.
More efficient than removing them individually.
@override
void removeAll() {
  super.removeAll();
  _paintingOrder = null;
}