anchor.diff:    void _handleDragStart() {
       if (_fadePerformance.isAnimating)
         return;
  -    _dragUnderway = true;
  -    _dragExtent = 0.0;
  -    _fadePerformance.progress = 0.0;
  +    setState(() {
  +      _dragUnderway = true;
  +      _dragExtent = 0.0;
  +      _fadePerformance.progress = 0.0;
  +    });
     }
   
     void _handleDragUpdate(double scrollOffset) {
  
positive.code:         break;
      }
  
      if (oldDragExtent.sign != _dragExtent.sign)
        setState(() {}); // Rebuild to update the new drag endpoint.
      if (!_fadePerformance.isAnimating)
        _fadePerformance.progress = _dragExtent.abs() / (_size.width * _kDismissCardThreshold);
    }
  
negative.code:       _startResizePerformance();
    }
  
    bool get _isActive {
      return _size != null && (_dragUnderway || _fadePerformance.isAnimating);
    }
  