Infinite-scroll listview.builder - to expand or not to expand... and more provider value not updating and how to fix "RenderFlex overflowed" - flutter

Question

I am trying to build a view/route that will list items fetched from a REST source.
I want to show a notification item below the list while the data is being fetched.
But my ListView builder is constructed around the fetched data's structure, so I figured just have a ListTile fit some appropriate UX elements below the generated list inside a Column - which was kinda working great - or so I thought - until the list grows to fill the screen causing RenderFlex overflowed error. Wrapping the ListView builder in Expanded fixed that but moved the indicator to the bottom of the screen.
In trying to fix it I seem to have broken more of the plumbing and the boolean variable that should control the idicator widget; isLoading: stockSet.isBusyLoading doesn't seem to update.
At the moment if I hardcode it as `` it does sit in the appropraite position but I am back with the RenderFlex overflow.
Once all of this is working I'll be wanting to automatically load items untill the screen is full - not sure where I'll be triggering that from yet.
class MyStockSet extends StatefulWidget {
const MyStockSet({super.key});
static const indexStr = 'stocks';
static const labelStr = 'Properties';
#override
State<MyStockSet> createState() => _MyStockSetState();
}
class _MyStockSetState extends State<MyStockSet> {
#override
Widget build(BuildContext context) {
const String imagePath = 'assets/images/${MyStockSet.indexStr}.png';
var assetImage = const AssetImage(imagePath);
//var stockSet = context.watch<StockSet>(); <- didn't work either
var stockSet = Provider.of<StockSet>(context,listen: false);
return Scaffold(
appBar: AppBar(
title: Row(
children: [
AscHero(
assetImage: assetImage,
tag: MyStockSet.indexStr,
title: MyStockSet.labelStr,
radius: 32,
),
const SizedBox(width: 12),
const Text(MyStockSet.labelStr),
],
),
actions: [
IconButton(
onPressed: () {
var stockSet = context.read<StockSet>();
int newNr = stockSet.stocks.length + 1;
Stock tmpstock = Stock(
id: newNr,
title: 'test$newNr',
thumbUrl: 'url',
description: 'desc');
stockSet.add(tmpstock);
},
icon: const Icon(Icons.add),
),
IconButton(
onPressed: () {
developer.log('btn before isBusyLoading ${stockSet.isBusyLoading}');
stockSet.fetch();
developer.log('after btn isBusyLoading ${stockSet.isBusyLoading}');
},
icon: const Icon(Icons.handshake),
),
],
),
body: Column(
children: [
Row(
// these will be filters, order toggle etc.
children: [
ElevatedButton(
onPressed: () => developer.log('Btn pressed.'),
child: Text('Btn')),
],
),
Expanded(
child: Column(children: [
_StockListView(),
LoadingStockListItemNotif(
isLoading: true,
),
]),
),
],
),
);
}
}
class _StockListView extends StatefulWidget {
#override
State<_StockListView> createState() => _StockListViewState();
}
class _StockListViewState extends State<_StockListView> {
#override
void didChangeDependencies() {
super.didChangeDependencies();
developer.log('_StockListView didChangeDependencies()');
// developer.log('scroll pos ${_scrollController.position}');
}
#override
Widget build(BuildContext context) {
var stockSet = context.watch<StockSet>();
return ListView.builder(
// controller: _scrollController,
shrinkWrap: true,
itemCount: stockSet.stocks.length,
itemBuilder: (context, index) => InkWell(
child: StockListItem(
stock: stockSet.stocks[index],
),
onTap: () => Navigator.pushNamed(
context,
'/stocks/stock',
arguments: ScreenArguments(stockSet.stocks[index]),
),
),
);
}
void _scrollListener() {
developer.log('_scrollListener');
}
}
and
class StockSet extends ChangeNotifier {
final List<Stock> _stocks = [];
late bool isBusyLoading = false;
List<Stock> get stocks => _stocks;
void add(Stock stock) {
_stocks.add(stock);
developer.log('added stock :${stock.title}');
notifyListeners();
}
void remove(Stock stock) {
_stocks.remove(stock);
notifyListeners();
}
Future<void> fetch() async {
developer.log('fetch() iL T');
isBusyLoading = true;
notifyListeners();
Stock tmpStock = await _fetchAStock();
developer.log('fetch() iL F');
isBusyLoading = false;
notifyListeners();
add(tmpStock);
}
Future<Stock> _fetchAStock() async {
developer.log('fetch stock ');
final response = await http.get(
Uri.https(
//...
),
);
developer.log('response.statusCode:${response.statusCode}');
if (response.statusCode == 200) {
final Map<String, dynamic> map = json.decode(response.body);
return Stock(
id: map['id'] as int,
title: map['title'] as String,
description: map['description'] as String,
thumbUrl: map['thumbUrl'] as String,
);
}
throw Exception('error fetching stocks:');
}
}
Apologies for the convoluted question.

Answer 1

Add mainAxisSize : MainAxisSize.min for the column inside the expanded widget. The expanded doesn't have any bounds and that's why it throws an error. You can wrap the column with a SingleChildScrollView if you have long content to display

Answer 2

This worked for me!
Just set the shrinkWrap attribute to true

Answer 3

Main lesson:
Don't fight the framework.
Answer:
Instead of tying yourself into Möbius knots trying to put the ListView's functionality outside of itself; use the fact that the ListView.builder allows you to sculpt the logic of how it gets built and what it will contain - given that the provider can trigger its rebuild when the variable in the data set changes.
In other words; by increasing the loop of the builder, you can insert a kind of footer to the Listview. The appearance (or not) of that can depend on the provider, provided it fires the appropriate notifyListeners()s etc.
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:equatable/equatable.dart';
import 'dart:async';
class ItemSetRoute extends StatefulWidget {
const ItemSetRoute({Key? key}) : super(key: key);
#override
State<ItemSetRoute> createState() => _ItemSetRouteState();
}
class _ItemSetRouteState extends State<ItemSetRoute> {
#override
Widget build(BuildContext context) {
var itemSet = Provider.of<ItemSet>(
context,
listen: true /* in order to rebuild */,
);
return Scaffold(
appBar: AppBar(title: const Text('Test'), actions: [
IconButton(
onPressed: () {
itemSet.fetch();
},
icon: const Icon(Icons.download),
)
]),
body: Column(
//screen
children: [
Row(
children: [
ElevatedButton(
onPressed: () {
itemSet.fetch();
},
child: const Text('Btn')),
],
),
Expanded(
child: ListView.builder(
scrollDirection: Axis.vertical,
shrinkWrap: true,
itemCount: itemSet.items.length + 1,
itemBuilder: (context, index) {
/* logic here to create a kind of footer of the ListView */
if (index <= itemSet.items.length - 1) {
return InkWell(
child: ItemListItem(
item: itemSet.items[index],
),
onTap: () {
//('Item tapped, navigate etc.');
});
} else {
return LoadingItemNotifier(
isLoading: itemSet.isBusyLoading,
);
}
},
),
),
],
),
);
}
}
//Models
class ItemListItem extends StatelessWidget {
const ItemListItem({Key? key, required this.item}) : super(key: key);
final Item item;
#override
Widget build(BuildContext context) {
return Material(
child: ListTile(
title: Text(item.title),
subtitle: Text(item.description),
),
);
}
}
class LoadingItemNotifier extends StatefulWidget {
const LoadingItemNotifier({Key? key, this.isLoading = false})
: super(key: key);
final bool isLoading;
#override
State<LoadingItemNotifier> createState() => _LoadingItemNotifierState();
}
class _LoadingItemNotifierState extends State<LoadingItemNotifier> {
#override
Widget build(BuildContext context) {
if (widget.isLoading) {
return Material(
child: ListTile(
leading: SizedBox(
width: 48,
height: 48,
child: ClipOval(
child: Material(
color: Colors.lightBlue.withOpacity(0.25),
child: const Center(
child: Icon(Icons.download),
),
),
),
),
title: const Text('Loading'),
isThreeLine: true,
subtitle: const Text('One moment please...'),
dense: true,
),
);
} else {
return const SizedBox(height: 0);
}
}
}
class ItemSet extends ChangeNotifier {
final List<Item> _items = [];
late bool isBusyLoading = false;
List<Item> get items => _items;
void add(Item item) {
_items.add(item);
notifyListeners();
}
void remove(Item item) {
_items.remove(item);
notifyListeners();
}
Future<void> fetch() async {
isBusyLoading = true;
notifyListeners();
/* handling REST call here */
await Future.delayed(const Duration(milliseconds: 500));
Item newItem = const Item(id: 123, title: 'Title', description: 'Desc');
isBusyLoading = false;
add(newItem);
}
}
class Item extends Equatable {
const Item({
required this.id,
required this.title,
required this.description,
});
final int id;
final String title;
final String description;
#override
List<Object> get props => [id, title, description];
}
Caveats
I don't know if this is the most efficient way of doing this - perhaps there should be fewer states, etc. ...