当滚动条位于列表底部时，颤振中的启用按钮

Question

当滚动条位于列表底部时，任何人都可以发布示例颤振代码以启用按钮吗？

我使用了通知侦听器和通知侦听器，但是当滚动条位于列表底部时，事件没有触发。

我只想仅在滚动条位于列表底部时才启用该按钮，否则应将其禁用。

下面是我正在使用的代码。

class _TermsAndCondnsPage extends State<TermsAndCondnsPage> {
bool _isButtonEnabled = false;
bool _scrollingStarted() {
setState(() => _isButtonEnabled = false);
return false;
}
bool _scrollingEnded() {
setState(() => _isButtonEnabled = true);
return true;
}
ScrollController scrollcontroller;
@override
Widget build(BuildContext context) {
var acceptAndContinueButtonPressed;
if (_isButtonEnabled) {
acceptAndContinueButtonPressed = () {};
} else {
acceptAndContinueButtonPressed == null;
}
return new Scaffold(
appBar: new AppBar(
automaticallyImplyLeading: false,
title: new Text('Terms And Conditions', textAlign: TextAlign.center),
),
body:
NotificationListener<ScrollStartNotification>(
onNotification: (_) => _scrollingStarted(),
child: NotificationListener<ScrollEndNotification>(
onNotification: (_) => _scrollingEnded(),
child: new MaterialApp(
home: new Scaffold(
body: new SingleChildScrollView(
controller: scrollcontroller,
child: new Column(
children: <Widget>[
new Center(
child: new HtmlView(
data: html,
),
),
],
),
),
persistentFooterButtons: <Widget>[
new RaisedButton(
color: Colors.blue,
onPressed: _isButtonEnabled ? () {} : null,
child: new Text(
'Accept and Continue',
style: new TextStyle(
color: Colors.white,
),
)),
],
),
),
)),
);
}
String html = '''
<p>Sample HTML</p>
''';
}

Answer 1

这里有一个基本示例，到达底部时启用按钮，到达顶部时禁用按钮。

class ExampleState extends State<Example> {
final list = List.generate((40), (val) => "val $val");
final ScrollController _controller = new ScrollController();
var reachEnd = false;
_listener() {
final maxScroll = _controller.position.maxScrollExtent;
final minScroll = _controller.position.minScrollExtent;
if (_controller.offset >= maxScroll) {
setState(() {
reachEnd = true;
});
}
if (_controller.offset <= minScroll) {
setState(() {
reachEnd = false;
});
}
}
@override
void initState() {
_controller.addListener(_listener);
super.initState();
}
@override
void dispose() {
_controller.removeListener(_listener);
_controller.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return Stack(children: [
Positioned(
top: 0.0,
bottom: 50.0,
width: MediaQuery.of(context).size.width,
child: ListView.builder(
controller: _controller,
itemBuilder: (context, index) {
return ListTile(
title: Text(list[index]),
);
},
itemCount: list.length,
),
),
Align(
alignment: Alignment.bottomCenter,
child: RaisedButton(
child: Text("button"),
color: Colors.blue,
onPressed: reachEnd ? () => null : null,
))
]);
}
}