flutter标题栏滑动隐藏显示

 ScrollController _scrollController = ScrollController();
  int _titleAlpha = 0; //范围 0-255

使用 ScrollController 来监听滚动事件，在initState()方法中增加监听

   _scrollController
      ..addListener(() {
        setState(() {
          if (_scrollController.offset > titleHeight) {
            _titleAlpha = 255;
          } else if (_scrollController.offset <= 0) {
            _titleAlpha = 0;
          } else {
            _titleAlpha = _scrollController.offset * 255 ~/ titleHeight;
          }
        });
      });

最后设置颜色为Colors.white.withAlpha(_titleAlpha)