为什么提供商有时不起作用？

Question

提供商的行为非常奇怪，当添加产品时，Isempty属性会发生变化，但没有调用提供商，当删除产品时，称为提供商，该行为的原因是什么。 有一个带价格的按钮，当按下noincart时，该按钮会添加一个产品，并且按钮上的文字更改，如果有产品，则该按钮具有两个区域incart 代码>，左侧区域删除了产品，右侧添加了更多，如果单击左侧，则按需按下按钮更改。

class AllGoodsViewModel extends ChangeNotifier {

   var _isEmpty = true;
   bool get isEmpty => _isEmpty;

   void detailSetting(Goods item) {
      final ind = cart.value.indexWhere((element) => element.id == item.id);
      if (ind != -1) {
        changeButtonState(false);
      } else {
        changeButtonState(true);
      }
    }

   void changeButtonState(bool state) {
     _isEmpty = state;
     notifyListeners();
   }
}

// adds and reduces a product
  void haveItem({required Goods item, required int operation}) async {
    final ind = cart.value.indexWhere((element) => element.id == item.id);
    if (ind == -1) {
      final minCount = item.optState == 0 ? 1 : item.opt!.count;
      if (item.count < minCount) {
        //order.shake();
      } else {
        changeButtonState(false); --------- cart is not empty, not working
        cart.value.add(item);
        final ind = cart.value.length - 1;
        cart.value.last.isOpt = item.optState == 0 ? false : true;
        cart.value.last.orderCount = minCount;
        cart.value = List.from(cart.value);
        await SQFliteService.cart.addToCart(cart.value.last);
        changeCountInCart(operation);
      }
    }  else {
      final count = cart.value[ind].orderCount;
      if (count <= item.count) {} else { return; } //order.shake()
      if (operation < 0 || count + operation <= item.count) {} else { return; } //order.shake()
      changeButtonState(false); --------- cart is not empty, not working
      cart.value[ind].orderCount += operation;
      cart.value = List.from(cart.value);
      await SQFliteService.cart.updateItem(cart.value[ind].id, {"orderCount":cart.value[ind].orderCount});
      changeCountInCart(operation);
    }
  }

class _DetailGoodsPageState extends State<DetailGoodsPage> {

  GlobalKey _key = GlobalKey();

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((_){
      Provider.of<AllGoodsViewModel>(context, listen: false).detailSetting(widget.item);
    });
  }


  @override
  Widget build(BuildContext context) {

    final model = Provider.of<AllGoodsViewModel>(context, listen: false);

    Widget inCart(){
      return GestureDetector(
          onPanDown: (details) {
            Goods? item = widget.item;
            RenderBox _cardBox = _key.currentContext!.findRenderObject() as RenderBox;
            final localPosition = details.localPosition;
            final localDx = localPosition.dx;
            if (localDx <= _cardBox.size.width/2) {
              Goods value = cart.value.firstWhere((element) => element.id == item.id);
              if (item.optState == 0 ? value.orderCount <= 1 : value.orderCount <= value.opt!.count) {
                setState(() {
                  final ind = cart.value.indexWhere((element) => element.id == item.id);
                  if (ind != -1) {
                    model.changeButtonState(true); ------ cart is empty it works
                    cart.value[ind].orderCount = 0;
                    SQFliteService.cart.delete(cart.value[ind].id);
                    cart.value = List.from(cart.value)..removeAt(ind);
                  }
                });
              } else {
                model.haveItem(item: item, operation: item.optState == 0 ? -1 : (-1 * value.opt!.count));
              }
            } else {
              model.haveItem(item: item, operation: item.optState == 0 ? 1 : item.count);
            }
          },
          child: ...
      );
    }

    Widget noInCart(){
      return Container(
        width: size.width - 16.w,
        margin: EdgeInsets.symmetric(vertical: 10.h),
        key: _key,
        child: TextButton(
            style: ButtonStyle(
                backgroundColor: MaterialStateProperty.all(Design.appColor),
                padding: MaterialStateProperty.all(EdgeInsets.symmetric(vertical: 8.h, horizontal: 10.w)),
                shape: MaterialStateProperty.all(RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(10.h),
                ))
            ),
            onPressed: (){
              Goods? item = widget.item;
              model.haveItem(item: item, operation: item.optState == 0 ? 1 : item.count);
            },
            child: ...
        ),
      );
    }

 return ScreenUtilInitService().build((context) => Scaffold(
      backgroundColor: Colors.white,
      body: Container(
              height: 64.h,
              color: Colors.white,
              child: model.isEmpty ? noInCart() : inCart()
          )

Answer 1

为了

更新

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Consumer<yourproviderclass>(
   builder: (context, yourproviderclassinstance, child) => widget,
 ),