Determine Scroll Widget height - flutter

Question

I would like to determine if a 'scrollable' widget indeed needs to scroll. I would ultimately like to show something like 'Scroll for more'. How do I achieve this?
I could use a combination of LayoutBuilder and a ScrollController. However, ScrollController gives me maxScrollExtent and minScrollExtent only after any event - like say for example user trying to scroll
I would like to know during 'build' so that I can determine to show 'Scroll for more' or not depending on the screen dimensions
class _MyHomePageState extends State<MyHomePage> {
int value = 0;
String text = 'You have pushed the button 0 times\n';
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Expanded(
flex: 9,
child: SingleChildScrollView(
child: Text(text),
),
),
Expanded(
flex: 1,
child: Text('Scroll for more')),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: () {
setState(() {
value += 1;
text = text + 'You have pushed the button $value times \n';
});
},
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
I would like to dynamically display
Text('Scroll for more'),
only if the SingleChildScrollView needs to be scrolled to view the entire content. Please note, I am just giving the above code as example.
In my real case, I have a StreamBuilder inside a SingleChildScrollView and I cannot determine how much of data is going to be flowing in from the stream. I also do not have any button or tap or any gesture to access the controller and setState
Thanks in advance for any help

Answer 1

class _MyHomePageState extends State<MyHomePage> {
bool showMore = false;
final scrollController = ScrollController();
#override
Widget build(BuildContext context) {
SchedulerBinding.instance.addPostFrameCallback((_) {
setState(() {
showMore = scrollController.position.maxScrollExtent > 0;
});
});
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Expanded(
flex: 9,
child: SingleChildScrollView(
controller: scrollController,
child: SizedBox(height: 650, child: Text('blah')),
),
),
if (showMore) Expanded(flex: 1, child: Text('Scroll for more')),
],
),
),
);
}
}