问题
How can I show a Container with animation on scrolling ListView down and hide it when scrolling up.
The video I am attaching is not exact implementation I want but it is just to give you an idea.
Sample video
https://imgur.com/a/auEzJQk
Edit:
Every time I scroll down, I need to show the Container and every time I scroll up, I want to hide it. It shouldn't depend on the index of the ListView.
回答1:
Not sure if I got your question properly, is this what you are trying to achieve?
Screenshot:
Code:
class HomePage extends StatefulWidget {
@override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
// Height of your Container
static final _containerHeight = 100.0;
// You don't need to change any of these variables
var _fromTop = -_containerHeight;
var _controller = ScrollController();
var _allowReverse = true, _allowForward = true;
var _prevOffset = 0.0;
var _prevForwardOffset = -_containerHeight;
var _prevReverseOffset = 0.0;
@override
void initState() {
super.initState();
_controller.addListener(_listener);
}
// entire logic is inside this listener for ListView
void _listener() {
double offset = _controller.offset;
var direction = _controller.position.userScrollDirection;
if (direction == ScrollDirection.reverse) {
_allowForward = true;
if (_allowReverse) {
_allowReverse = false;
_prevOffset = offset;
_prevForwardOffset = _fromTop;
}
var difference = offset - _prevOffset;
_fromTop = _prevForwardOffset + difference;
if (_fromTop > 0) _fromTop = 0;
} else if (direction == ScrollDirection.forward) {
_allowReverse = true;
if (_allowForward) {
_allowForward = false;
_prevOffset = offset;
_prevReverseOffset = _fromTop;
}
var difference = offset - _prevOffset;
_fromTop = _prevReverseOffset + difference;
if (_fromTop < -_containerHeight) _fromTop = -_containerHeight;
}
setState(() {}); // for simplicity I'm calling setState here, you can put bool values to only call setState when there is a genuine change in _fromTop
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text("ListView")),
body: Stack(
children: <Widget>[
_yourListView(),
Positioned(
top: _fromTop,
left: 0,
right: 0,
child: _yourContainer(),
)
],
),
);
}
Widget _yourListView() {
return ListView.builder(
itemCount: 100,
controller: _controller,
itemBuilder: (_, index) => ListTile(title: Text("Item $index")),
);
}
Widget _yourContainer() {
return Opacity(
opacity: 1 - (-_fromTop / _containerHeight),
child: Container(
height: _containerHeight,
color: Colors.red,
alignment: Alignment.center,
child: Text("Your Container", style: TextStyle(fontSize: 32, fontWeight: FontWeight.bold, color: Colors.white)),
),
);
}
}
回答2:
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
const double HEIGHT = 96;
final ValueNotifier<double> notifier = ValueNotifier(0);
return MaterialApp(
debugShowCheckedModeBanner: false,
home: Scaffold(
appBar: AppBar(title: const Text('Test')),
body: Stack(
children: [
NotificationListener<ScrollNotification>(
onNotification: (n) {
if (n.metrics.pixels <= HEIGHT) {
notifier.value = n.metrics.pixels;
}
return false;
},
child: ListView.builder(
itemCount: 42,
itemBuilder: (context, index) {
return Container(
height: 64,
padding: const EdgeInsets.all(16),
alignment: Alignment.centerLeft,
child: Text('Item $index'),
);
},
),
),
HideableWidget(height: HEIGHT, notifier: notifier),
],
),
),
);
}
}
class HideableWidget extends StatelessWidget {
final double height;
final ValueNotifier<double> notifier;
HideableWidget({@required this.height, @required this.notifier});
@override
Widget build(BuildContext context) {
return ValueListenableBuilder<double>(
valueListenable: notifier,
builder: (context, value, child) {
return Transform.translate(
offset: Offset(0, value - height),
child: Container(
height: 80,
color: Colors.red,
),
);
},
);
}
}
回答3:
I got the solution of your problem. Here is the demo code
class _DemoState extends State<WidgetDemo> {
ScrollController scrollController = new ScrollController();
bool isVisible = true;
@override
initState() {
super.initState();
scrollController.addListener(() {
if (scrollController.position.userScrollDirection ==
ScrollDirection.reverse) {
if (isVisible)
setState(() {
isVisible = false;
});
}
if (scrollController.position.userScrollDirection ==
ScrollDirection.forward) {
if (!isVisible)
setState(() {
isVisible = true;
});
}
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
body: Stack(
children: <Widget>[
new CustomScrollView(
controller: scrollController,
shrinkWrap: true,
slivers: <Widget>[
new SliverPadding(
padding: const EdgeInsets.all(20.0),
sliver: new SliverList(
delegate: new SliverChildListDelegate(
<Widget>[
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
const Text('My temp data'),
const Text('Wow its working'),
],
),
),
),
],
),
AnimatedContainer(
duration: Duration(milliseconds: 400),
height: isVisible ? 60.0 : 0.0,
child: new Container(
color: Colors.green,
width: MediaQuery.of(context).size.width,
child: Center(child: Text("Container")),
)),
],
),
);
}
}
来源：https://stackoverflow.com/questions/58254569/flutter-show-and-hide-container-on-scrolling-listview