startanimation

startanim.dart

 void _startAnimation(AnimationController _controller) {
    _controller.fling(
        velocity:isBackpanelVisible(widget._controller) ? -1.0 : 1.0);
  }
  
   bool isBackpanelVisible(AnimationController _controller) {
    final AnimationStatus status =_controller.status;
    return status == AnimationStatus.completed ||
        status == AnimationStatus.forward;
  }