@Override
  public void onDraw() {
    // draw is only expected if the controller is attached
    if (mIsControllerAttached) {
      return;
    }

    // something went wrong here; controller is not attached, yet the hierarchy has to be drawn
    // log error and attach the controller
    FLog.w(
        DraweeEventTracker.class,
        "%x: Draw requested for a non-attached controller %x. %s",
        System.identityHashCode(this),
        System.identityHashCode(mController),
        toString());

    mIsHolderAttached = true;
    mIsVisible = true;
    attachOrDetachController();
  }
Callback used to notify about top-level-drawable being drawn.
drawee/src/main/java/com/facebook/drawee/view/DraweeHolder.java