Appbar getting trasnparent and shows content under it

I am trying to achieve appbar animation. I have achieved the animation required but app bar is getting transparent. I dont know why this is happening. Can someone help resolving the issue?

Here is the code

  bool showAppbar = false;
  bool isScrollingDown = true;
  ScrollController controller = ScrollController();

  @override
  void initState() {
    super.initState();
    controller.addListener(() {
      if (controller.position.userScrollDirection == ScrollDirection.forward) {
        if (!isScrollingDown) {
          isScrollingDown = true;
          showAppbar = false;
          setState(() {});
        }
      }

  if (controller.position.userScrollDirection == ScrollDirection.reverse) {
    if (isScrollingDown && controller.position.pixels > 200) {
      isScrollingDown = false;
      showAppbar = true;
      setState(() {});
    }
  }
});


}



@override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          children: [
            Expanded(
              child: Stack(
                children: [
                  AnimatedContainer(
                    duration: const Duration(
                      milliseconds: 150,
                    ),
                    height: showAppbar ? 90 : 0,
                    child: AppBar(
                      title: Text(widget.title),
                      backgroundColor: Colors.redAccent,
                    ),
                  ),
                  Expanded(
                    child: ListView.builder(
                      itemBuilder: (context, index) {
                        return Text("data $index");
                      },
                      itemCount: 60,
                      controller: controller,
                    ),
                  ),
                ],
              ),
            ),
          ],
        ),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }

This is the result

I dont want the Listview rows showing behind the appbar.

>Solution :

You need to change the order inside your stack widget:

Stack(
        children: [
          Expanded(
            child: ListView.builder(
              itemBuilder: (context, index) {
                return Text("data $index");
              },
              itemCount: 60,
              controller: controller,
            ),
          ),
          AnimatedContainer(
            duration: const Duration(
              milliseconds: 150,
            ),
            height: showAppbar ? 90 : 0,
            child: AppBar(
              title: Text(widget.title),
              backgroundColor: Colors.redAccent,
            ),
          ),
        ],
      )