attach method

  1. @mustCallSuper
void attach (covariant Object owner)
@mustCallSuper

Mark this node as attached to the given owner.

Typically called only from the parent's attach method, and by the owner to mark the root of a tree as attached.

Subclasses with children should override this method to first call their inherited attach method, and then attach all their children to the same owner.

Implementation 

@mustCallSuper
void attach(covariant Object owner) {
  assert(owner != null);
  assert(_owner == null);
  _owner = owner;
}