Flutter - Provider does not updating data - flutter

Question

I am using Provider to ensure data consistency between widgets. I just learned that the level of declared Provider object is important when accessing data in widgets. So I created one Provider variable at the top and tried to pass it as an argument to children, stateless & stateful widgets.
In a stateful widget, user selects size for a product. In a stateless widget, user taps button to add the selected item with selected specification to cart. Afterwards, API handles all stuff but to that point, when user selects other sizes, Provider does not update the initial data it holds. It always stuck with initial data or in my case initial size of a product.
Here is my: top parent widget:
#override
Widget build(BuildContext context) {
// initialize
var provider = Provider.of<ProductDetailProvider>(context, listen: true);
provider.detailModel = widget.detailModel!;
provider.seciliBeden = int.parse(widget.detailModel!.Stoks.first.Beden);
provider.stokId = -1;
return Scaffold(
backgroundColor: AppTheme.containerColor,
body: SafeArea(
bottom: false,
child: Container(
height: MediaQuery.of(context).size.height,
width: MediaQuery.of(context).size.width,
child: Stack(
children: [
ImageViewBuilder(
pageController: imagePageController,
productDetailModel: widget.detailModel,
resims: resims,
),
DraggableScrollableSheet(
initialChildSize: 0.3,
maxChildSize: 1,
minChildSize: 0.3,
builder: (context, controller) {
return DraggableProductView(
scrollController: controller,
detailModel: widget.detailModel,
provider: provider, // StatefulWidget
);
},
),
Positioned(
child: Align(
alignment: Alignment.bottomCenter,
child: AddToCartBottomBar(
productDetailModel: widget.detailModel!,
productDetailProvider: provider, //StatelessWidget
),
),
),
],
),
),
),
);
}
StatefulWidget: this is how I change Provider object in DraggableProductView:
onTap: () {
setState(() {
seciliBeden =
widget.detailModel!.Stoks[index].Beden;
});
widget.provider!
.changeSeciliBeden(int.parse(seciliBeden));
},
Inside this StatefulWidget, I can print updated provider with updated datas. ChangeSeciliBeden also triggers ChangeStockId function inside provider.
StatelessWidget: AddToCartBottom widget holds several stateless widgets. This is the onTap method from AddToCartButton:
onTap: () async {
// This line prints only initial size & stock id of the product.
// It does not print updated data
print("yukarı: ${productDetailProvider!.stokId}");
// ...
// ...
// ...
},
Finally, this is my provider class:
class ProductDetailProvider extends ChangeNotifier {
late ProductDetailModel detailModel;
late int seciliBeden;
late int stokId;
// This method works too. It prints updated data.
changeSeciliBeden(int value) {
seciliBeden = value;
prepareStokId();
print("provider secili beden: $seciliBeden");
print("provider stok id: $stokId");
notifyListeners();
}
changeStokId(int value) {
stokId = value;
notifyListeners();
}
// This method works. I checked that. If block is true always once.
prepareStokId() {
detailModel.Stoks.forEach((element) {
if (element.Beden == seciliBeden.toString()) {
changeStokId(element.StokId);
}
});
notifyListeners();
}
}
Can somebody help me to figure out where I did wrong? Isn't this the way to pass data between widgets without using arguments?