屏幕截图(空安全+优化)
代码:
class MyPage extends StatefulWidget {
@override
State<MyPage> createState() => _MyPageState();
}
class _MyPageState extends State<MyPage> {
late final ScrollListener _model;
late final ScrollController _controller;
final double _bottomNavBarHeight = 56;
@override
void initState() {
super.initState();
_controller = ScrollController();
_model = ScrollListener.initialise(_controller);
}
@override
Widget build(BuildContext context) {
return Scaffold(
body: AnimatedBuilder(
animation: _model,
builder: (context, child) {
return Stack(
children: [
ListView.builder(
controller: _controller,
itemCount: 20,
itemBuilder: (_, i) => ListTile(title: Text('Item $i')),
),
Positioned(
left: 0,
right: 0,
bottom: _model.bottom,
child: _bottomNavBar,
),
],
);
},
),
);
}
Widget get _bottomNavBar {
return SizedBox(
height: _bottomNavBarHeight,
child: BottomNavigationBar(
backgroundColor: Colors.amber,
items: [
BottomNavigationBarItem(icon: Icon(Icons.call), label: 'Call'),
BottomNavigationBarItem(icon: Icon(Icons.message), label: 'Message'),
],
),
);
}
}
class ScrollListener extends ChangeNotifier {
double bottom = 0;
double _last = 0;
ScrollListener.initialise(ScrollController controller, [double height = 56]) {
controller.addListener(() {
final current = controller.offset;
bottom += _last - current;
if (bottom <= -height) bottom = -height;
if (bottom >= 0) bottom = 0;
_last = current;
if (bottom <= 0 && bottom >= -height) notifyListeners();
});
}
}