anchor.diff:      this.onPageChanged,
       this.scaleStateChangedCallback,
       this.enableRotation = false,
  +    this.defaultPageIndex = 0,
     }) : super(key: key);
   
     /// A list of options to describe the items in the gallery
  
positive.code:     _controller = widget.pageController ?? PageController();
      _locked = false;
      super.initState();
    }
  
    void scaleStateChangedCallback(PhotoViewScaleState scaleState) {
  
negative.code:   /// Mirror to [PhotoView.enableRotation]
    final bool enableRotation;
  
    /// An index of the [PageView] inside [PhotoViewGallery]
    final int defaultPageIndex;
  
    @override
    State<StatefulWidget> createState() {
      return _PhotoViewGalleryState();
  