Test example of using webview with floating app bar on Flutter

flutter_webview_with_appbar.dart

...

AnimationController? _hidePanelController;
double _hidePanelsValue = 0.0;
String _url = 'https://flutter.dev/';

@override
void initState() {
  super.initState();
  _hidePanelController = new AnimationController(vsync: this);
}

@override
Widget build(BuildContext context) {
  return Stack(children: [
    /// Webview with touch listener
    AnimatedBuilder(
        animation: _hidePanelController!,
        builder: (context, c) {
          return Scaffold(
            /// Empty space for floating appbar
            appBar: PreferredSize(
              preferredSize: Size(
                  MediaQuery.of(context).size.width, (kToolbarHeight - 1) * (1 - _hidePanelController!.value)),
              child: Container(),
            ),

            body: Listener(
              onPointerMove: (_) {
                /// Hide panel
                ///

                _hidePanelsValue -= _.delta.dy / 60;

                if (_hidePanelsValue > 1.0) _hidePanelsValue = 1.0;
                if (_hidePanelsValue < 0.0) _hidePanelsValue = 0.0;

                _hidePanelController?.value = _hidePanelsValue;
              },
              onPointerUp: (_) {
                /// Snap panels
                ///
                double _value = _hidePanelController!.value;
                if (_value != 0.0 && _value != 1.0) {
                  if (_value < 0.5) {
                    _hidePanelController?.animateTo(0, duration: Duration(milliseconds: 150), curve: Curves.easeIn);
                  } else {
                    _hidePanelController?.animateTo(1, duration: Duration(milliseconds: 150), curve: Curves.easeIn);
                  }
                }
              },
              child: InAppWebView(
                initialUrlRequest: URLRequest(url: _url),
              ),
            ),
          );
        }),

    /// Floating app bar
    Positioned(
      top: 0,
      right: 0,
      left: 0,
      child: AnimatedBuilder(
        animation: _hidePanelController!,
        builder: (context, child) => SlideTransition(
          position: Tween<Offset>(begin: const Offset(0, 0), end: Offset(0, -((kToolbarHeight / (kToolbarHeight + MediaQuery.of(context).padding.top)))))
              .animate(_hidePanelController!),
          child: ConstrainedBox(constraints: BoxConstraints(maxHeight: kToolbarHeight), child: AppBar(title: Text(_url))),
        ),
      ),
    ),
  ]);
}