getChildAt method
Implementation
@override
RenderViewModel? getChildAt(int index) {
  if (index >= 0 && index < childCount) {
    return _children[index];
  }
  return null;
}@override
RenderViewModel? getChildAt(int index) {
  if (index >= 0 && index < childCount) {
    return _children[index];
  }
  return null;
}