docs: public void captureChildView(View childView, int activePointerId) {
          if (childView.getParent() != mParentView) {
              throw new IllegalArgumentException("captureChildView: parameter must be a descendant " +
                      "of the ViewDragHelper's tracked parent view (" + mParentView + ")");
          }
  
          mCapturedView = childView;
          mActivePointerId = activePointerId;
          mCallback.onViewCaptured(childView, activePointerId);
          setDragState(STATE_DRAGGING);
      }