renderObject property

RenderObject renderObject

The render object at (or below) this location in the tree.

If this object is a RenderObjectElement, the render object is the one at this location in the tree. Otherwise, this getter will walk down the tree until it finds a RenderObjectElement.

Implementation 

RenderObject get renderObject {
  RenderObject result;
  void visit(Element element) {
    assert(result == null); // this verifies that there's only one child
    if (element is RenderObjectElement)
      result = element.renderObject;
    else
      element.visitChildren(visit);
  }
  visit(this);
  return result;
}