如何从 Riverpod 中的 StateNotifier 显示小吃店？

问题描述

我有以下课程工作正常。

class CartRiverpod extends StateNotifier<List<CartItemmodel>> {

    CartRiverpod([List<CartItemmodel> products]) : super(products ?? []);

        void add(ProductModel addProduct) {
            bool productExists = false;
                for (final product in state) {
                    if (product.id == addProduct.id) {
                        print("not added");
                        productExists = true;
                    }
                    else {
                    }
                 }
        if (productExists==false)
            {
                state = [
                    ...state,new CartItemmodel(product: addProduct),];
                print("added");
             }

    }

    void remove(String id) {
      state = state.where((product) => product.id != id).toList();
    }
  }

上面的代码完美运行。在我的购物车中，我想将产品的订单限制为 1 个单位，这就是我执行上述代码的原因。它按我的预期工作。 现在唯一的事情是，我想展示一个小吃店，提醒用户他或她只能订购 1 件产品。

如何在 StateNotifier 中添加小吃店？

解决方法

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/all.dart';
import 'package:freezed_annotation/freezed_annotation.dart';
part 'cart_list_page.freezed.dart';

final cartListPageStateNotifierProvider =
    StateNotifierProvider((ref) => CartListPageStateNotifier(ref.read));

final cartListProvider = StateProvider((ref) {
  return <CartListItemModel>[];
}); // this holds the cart list,at initial,its empty

class CartListPage extends StatefulWidget {
  @override
  _CartListPageState createState() => _CartListPageState();
}

class _CartListPageState extends State<CartListPage> {
  final _scaffoldKey = GlobalKey<ScaffoldState>();
  List<CartListItemModel> productsToBeAddedToCart = [
    CartListItemModel(id: 1,name: "Apple"),CartListItemModel(id: 2,name: "Tomatoes"),CartListItemModel(id: 3,name: "Oranges"),CartListItemModel(id: 4,name: "Ginger"),CartListItemModel(id: 5,name: "Garlic"),CartListItemModel(id: 6,name: "Pine"),];

  @override
  Widget build(BuildContext context) {
    return ProviderListener<CartListState>(
      provider: cartListPageStateNotifierProvider.state,onChange: (context,state) {
        return state.maybeWhen(
          loading: () {
            final snackBar = SnackBar(
              duration: Duration(seconds: 2),backgroundColor: Colors.yellow,content: Text('updating cart....'),);
            return _scaffoldKey.currentState.showSnackBar(snackBar);
          },success: (info) {
            final snackBar = SnackBar(
              duration: Duration(seconds: 2),backgroundColor: Colors.green,content: Text('$info'),);
            _scaffoldKey.currentState.hideCurrentSnackBar();
            return _scaffoldKey.currentState.showSnackBar(snackBar);
          },error: (errMsg) {
            final snackBar = SnackBar(
              duration: Duration(seconds: 2),backgroundColor: Colors.red,content: Text('$errMsg'),orElse: () => SizedBox.shrink(),);
      },child: Scaffold(
        key: _scaffoldKey,body: Container(
          height: MediaQuery.of(context).size.height,width: MediaQuery.of(context).size.width,child: Column(
            children: [
              SizedBox(height: 40),Expanded(
                child: ListView.builder(
                  itemCount: productsToBeAddedToCart.length,itemBuilder: (context,index) {
                    final item = productsToBeAddedToCart[index];
                    return ListTile(
                      title: Text("${item.name}"),leading: CircleAvatar(child: Text("${item.id}")),trailing: Row(
                        mainAxisSize: MainAxisSize.min,children: [
                          IconButton(
                            icon: Icon(Icons.add),onPressed: () => context
                                .read(cartListPageStateNotifierProvider)
                                .addProduct(item),),SizedBox(width: 2),IconButton(
                            icon: Icon(Icons.remove),onPressed: () => context
                                .read(cartListPageStateNotifierProvider)
                                .removeProduct(item),],);
                  },)
            ],);
  }
}

class CartListPageStateNotifier extends StateNotifier<CartListState> {
  final Reader reader;
  CartListPageStateNotifier(this.reader) : super(CartListState.initial());

  addProduct(CartListItemModel product) async {
    state = CartListState.loading();
    await Future.delayed(Duration(seconds: 1));
    var products = reader(cartListProvider).state;
    if (!products.contains(product)) {
      reader(cartListProvider).state.add(product);
      return state =
          CartListState.success("Added Successfully ${product.name}");
    } else {
      return state = CartListState.error(
          "cannot add more than 1 product of the same kind");
    }
  }

  removeProduct(CartListItemModel product) async {
    state = CartListState.loading();
    await Future.delayed(Duration(seconds: 1));
    var products = reader(cartListProvider).state;
    if (products.isNotEmpty) {
      bool status = reader(cartListProvider).state.remove(product);
      if (status) {
        return state =
            CartListState.success("removed Successfully ${product.name}");
      } else {
        return state;
      }
    }
    return state = CartListState.error("cart is empty");
  }
}

@freezed
abstract class CartListState with _$CartListState {
  const factory CartListState.initial() = _CartListInitial;
  const factory CartListState.loading() = _CartListLoading;
  const factory CartListState.success([String message]) = _CartListSuccess;
  const factory CartListState.error([String message]) = _CartListError;
}

@freezed
abstract class CartListItemModel with _$CartListItemModel {
  factory CartListItemModel({final String name,final int id}) =
      _CartListItemModel;
}