Understanding and implementing OOP (in flutter/dart) to abstract shared structure and functionality - flutter

Question

(Edited to clarify & update with progress)
When building an app with various lists of items and some cross-referencing between them; e.g. I have a stock class and a StockSet that extends ChangeNotifier as well as holds some basic rest functionality etc. But I'm also going to have Clients, Meetings etc, all of which are basically the same except for minor differences in fields.
So I recon I should define a parent class, say Item and ItemSet that, and then the actual elements in my app will extend those. - Or is that over-engineering?
However, in say my current StockSet I have methods to fetch either a single, or a number of stock items, i.e. ...Future<Stock> _fetchAStock() async {...
the only significant difference between it and say client records will be the REST url, and type of object returned (and give or take a few fields).
Is it better to have individual methods in all the child level classes - seems simpler though more code = more potential errors etc. OR build the fetch functionality into the parent class with some kind of abstraction/specification/parameterization(/or external configuration look-up) of the case specific differences?
New-ish to OOP and Flutter/Dart and it seems clearer some days than others... this is an others :-)
What I have:
class StocksSetRoute extends StatelessWidget with asc_alertBar {
const StocksSetRoute({Key? key}) : super(key: key);
static const indexStr = 'stocks';
static const labelStr = 'Properties';
static GlobalKey myKey = GlobalKey();
static GlobalKey parentKey = GlobalKey();
#override
Widget build(BuildContext context) {
var stockSet = context.watch<StockSet>();
return Scaffold(
key: parentKey,
appBar: AppBar(
title: const TitleRow(indexStr: indexStr, labelStr: labelStr),
),
body: Column(
mainAxisSize: MainAxisSize.min,
children: [
Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
// these will be filters, order toggle etc.
children: [
ElevatedButton(
onPressed: (stockSet.isRemoteEmpty)
? null
: () async {
try {
await stockSet.fetch(5);
} catch (e) {
alertBar(
'Could not fetch any more. ', stockSet as ItemSet,
backgroundColor: Colors.grey, context: context);
}
},
child: const Text('Fetch More'),
),
ElevatedButton(
onPressed:
(stockSet.stocks.isEmpty) ? null : () => stockSet.clear(),
child: const Text('Clear'),
),
],
),
Expanded(
child: StockListViewBuilder(
stockSet: stockSet, theKey: myKey, alert: alertBar))
],
),
);
}
}
class StockListViewBuilder extends StatefulWidget {
final StockSet stockSet;
final GlobalKey theKey;
final Function alert;
const StockListViewBuilder({
Key? key,
required this.stockSet,
required this.theKey,
required this.alert,
}) : super(key: key);
#override
State<StockListViewBuilder> createState() => _StockListViewBuilderState();
}
class _StockListViewBuilderState extends State<StockListViewBuilder>
with asc_alertBar {
final ScrollController _scrollController = ScrollController();
late double _scrollPosition;
late double _maxScrollExtent;
late bool isThisTheEnd = false;
_scrollListener() async {
setState(() {
_scrollPosition = _scrollController.position.pixels;
_maxScrollExtent = _scrollController.position.maxScrollExtent;
});
if (!isThisTheEnd && _scrollPosition / _maxScrollExtent > 0.90) {
isThisTheEnd = true;
if (widget.stockSet.isRemoteEmpty) {
alertBar('No more items available', null, context: context);
} else {
await widget.stockSet.fetch(5);
}
}
if (isThisTheEnd && _scrollPosition / _maxScrollExtent <= 0.90) {
isThisTheEnd = false;
}
}
#override
void initState() {
super.initState();
int listCount;
_scrollController.addListener(_scrollListener);
WidgetsBinding.instance.addPostFrameCallback((_) async {
listCount = widget.stockSet.stocks.length;
if (listCount < 10 && !widget.stockSet.isRemoteEmpty) {
try {
await widget.stockSet.fetch(10);
} catch (e) {
super.setState(() {
widget.alert("Can't load stock.", widget.stockSet,
backgroundColor: Colors.red);
});
}
}
});
}
#override
Widget build(BuildContext context) {
return ListView.builder(
scrollDirection: Axis.vertical,
controller: _scrollController,
shrinkWrap: true,
key: widget.theKey,
itemCount: widget.stockSet.stocks.length + 1,
itemBuilder: (context, index) {
if (index <= widget.stockSet.stocks.length - 1) {
return InkWell(
onTap: (() => Navigator.pushNamed(
context,
'/stocks/stock',
arguments: ScreenArguments(widget.stockSet.stocks[index]),
)),
child: StockListItem(
stock: widget.stockSet.stocks[index],
));
} else {
return LoadingItemNotifier(
isLoading: widget.stockSet.isBusyLoading,
);
}
},
);
}
}
class StockSet extends ItemSet {
final List<Stock> _stocks = [];
List<Stock> get stocks => _stocks;
List<int> getHaveStocksIds() {
final List<int> ids = _stocks.map((stock) => stock.id).toList();
return ids;
}
void add(Stock stock) {
_stocks.add(stock);
notifyListeners();
}
void remove(Stock stock) {
_stocks.remove(stock);
notifyListeners();
}
void clear() {
_stocks.clear();
isBusyLoading = false;
isRemoteEmpty = false;
notifyListeners();
}
Future<void> fetch([int num = 1]) async {
int i = 0;
for (i; i < num; i++) {
if (!isRemoteEmpty) {
try {
Stock tmpStock = await _fetchAStock();
if (getHaveStocksIds().contains(tmpStock.id)) {
throw Exception('We allready have ${tmpStock.id}');
}
add(tmpStock);
} catch (e) {
i = num;
isRemoteEmpty = true;
isBusyLoading = false;
notifyListeners();
throw Exception('No more to fetch $e');
}
}
}
return;
}
Future<Stock> _fetchAStock() async {
List<int> have = getHaveStocksIds();
final queryParameters = {
'exclude': json.encode(have),
};
isBusyLoading = true;
notifyListeners();
try {
final response = await http.post(
Uri.https('onethread.design', 'agency/wp-json/ypagp/v1/pr-get-a',
queryParameters),
);
isBusyLoading = false;
notifyListeners();
if (response.statusCode != 200) {
throw HttpException('${response.statusCode}');
}
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,
);
} on SocketException {
feedback = 'Please enable an internet connection.';
notifyListeners();
} on HttpException {
feedback = "Couldn't find the/a post.";
notifyListeners();
} on FormatException {
feedback = "Bad response format.";
} catch (e, s) {
feedback = 'fetchA catch $e $s ';
}
throw Exception('Could not _fetchAStock');
}
}
class ItemSet extends ChangeNotifier {
bool isBusyLoading = false;
bool isRemoteEmpty = false;
String? feedback;
}
what I'm aiming at (and have partially succeeded in implementing) is something like
class StockSet extends ItemSet and class ItemSet extends ChangeNotifier {...
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];
}
and I think then
class Stock extends Item {
final String thumbUrl;
const Stock(
{required super.id, required super.title, required super.description, required this.thumbUrl});
#override
List<Object> get props => [id, title, description, thumbUrl];
}
though when it comes to the ItemSet's methods, e.g.
been trying things like e.g.
in ItemSet
Future<Type> fetchAItem(String typeSlug, Type type) async {
List<int> have = getHaveItemsIds();
final queryParameters = {
'exclude': json.encode(have),
};
developer.log('_fetchAItem $queryParameters');
isBusyLoading = true;
notifyListeners();
try {
final response = await http.post(
Uri.https('###', 'a###/v1/$typeSlug-get-a',
queryParameters),
);
developer.log('response.statusCode:${response.statusCode}');
isBusyLoading = false;
notifyListeners();
if (response.statusCode != 200) {
throw HttpException('${response.statusCode}');
}
final Map<String, dynamic> map = json.decode(response.body);
return Item(
id: map['id'] as int,
title: map['title'] as String,
description: map['description'] as String,
) as type;// no! - was worth a guess though
} on...
but I'm getting lost in the plumbing, should I use #override in the child classes? seems clunky - or maybe use more mixins?.
Thanks in advance
and the alertBar mixin...
mixin asc_alertBar {
void alertBar(
String message,
ItemSet? itemSet, {
String label = 'Okay',
Function? action,
Color? backgroundColor,
required BuildContext context,
}) {
if (itemSet != null) {
String? itemSetFeedback = itemSet.feedback;
if (itemSetFeedback != null) {
message += '\n$itemSetFeedback';
itemSet.feedback = null;
}
}
ScaffoldMessenger.of(context).showSnackBar(
SnackBar(
backgroundColor: backgroundColor,
duration: const Duration(seconds: 15),
content: AnimatedText(
textContent: message,
durationFactor: 0.25,
),
action: SnackBarAction(
label: label,
onPressed: () => action,
),
),
);
}
}
I hope the question makes sense.