Question

我使用提供包（状态管理）创建了一个购物车应用，用于在购物车页面中存储所选商品或产品，但是问题是我收到“类型为String的错误，不是类型为Item的子类型”。下面是飞镖代码和模型，如果我尝试单击主页上的任何项目，则将所选项目存储在购物车页面中；如果我尝试存储第二个页面（数量页面）中的项目，则会出现错误。

HomePage.dart

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();}
class _HomeState extends State<Home> {
List<Item> _product=[
  Item(
    title: "Cake",
    image: "assets/1.png",
    price: 20.00,
  ),
  Item(
    title: "Pasteries",
    image: "assets/2.png",
    price: 30.00,
  ),];
  @override
  Widget build(BuildContext context) {
    return Consumer<Cart>(
      builder: (context,cart,child){
        return PlatformScaffold(
            body: ListView.builder(
                itemCount: _product.length,
                itemBuilder: (BuildContext context, int index) {
                  return Padding(
                    padding: const EdgeInsets.only(
                        top: 35.0, bottom: 15.0, left: 20.0, right: 20.0),
                    child: GestureDetector(
                      onTap: (){
                    //cart.add(_product[index]);//Here i try to select the item and it successfully stored in cart page
                    Navigator.of(context).push(MaterialPageRoute(builder: (context) => Quantities(
                      productname: _product[index].title,
                      productprice: _product[index].price,
                      productimage: _product[index].image,
                    )));},
                      child: Container(
                        child: new FittedBox(
                          child: Material(
                              color: Colors.white,
                              elevation: 15.0,
                              borderRadius: BorderRadius.circular(15.0),
                              shadowColor: Color(0x802196F3),
                              child: Column(
                                mainAxisAlignment: MainAxisAlignment.center,
                                children: <Widget>[
                                  Container(
                                    width: 250,
                                    height: 200,
                                    child: ClipRRect(
                                      borderRadius: new BorderRadius.circular(15.0),
                                      child: new Image.asset(
                                        _product[index].image,
                                        fit: BoxFit.cover,),),),
                                  Padding(
                                    padding: const EdgeInsets.only(top: 5.0,bottom: 5.0),
                                    child: Text(_product[index].title,style: TextStyle(color: Colors.blueGrey[700],
                                        fontWeight: FontWeight.bold,fontSize: 18.0),),
                                  ),],)),),),),);}));},);}}

Quantities.dart

class Quantities extends StatefulWidget {
  var productprice;
  String productimage;
  final productname;
  Quantities({this.productprice, this.productimage, this.productname});
  @override
  _QuantitiesState createState() => _QuantitiesState(productprice,productimage,productname);}
class _QuantitiesState extends State<Quantities> {
  final productprice;
  final productimage;
  final productname;
  _QuantitiesState(this.productprice, this.productimage, this.productname);
  @override
  Widget build(BuildContext context) {
    return Consumer<Cart>(
      builder: (context,cart,child){
        return PlatformScaffold(
          appBar: PlatformAppBar(
            backgroundColor: Colors.lightBlue[900],
            title: Text('Details'),),
          body: ListView(
            children: <Widget>[
              Padding(
                padding: const EdgeInsets.only(top: 20.0),
                child: Container(
                  child: Column(
                    children: <Widget>[
                      Container(
                        height: 150.0,
                        child: GridTile(
                          child: Container(
                            color: Colors.white,
                            child: Image.asset(productimage),),),),
                      Text(productname,style: TextStyle(fontWeight: FontWeight.bold, fontSize: 20.0),),
                      Text("Price: "+productprice.toString()+" SAR",style: TextStyle(fontWeight: FontWeight.bold, fontSize: 20.0),),
                      Padding(
                        padding: const EdgeInsets.only(top: 20.0),
                        child: Center(
                          child: PlatformButton(
                              onPressed: () {
                                cart.add(productname);},// Here i am getting an error
                              child: Text('Add to Cart',style: TextStyle(color: Colors.white),),
                              androidFlat: (_) => MaterialFlatButtonData(
                                  color: Colors.cyan),
                              ios: (_) => CupertinoButtonData(
                                  color: Colors.cyan
                              )),),),],),),),],),);},);}}

CartPage.dart

class CartPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _CartPageState();}}
class _CartPageState extends State<CartPage> {
  @override
  Widget build(BuildContext context) {
    return Consumer<Cart>(
      builder: (context,cart,child){
        return Scaffold(
          appBar: AppBar(
            backgroundColor: Colors.indigo,
            title: Text("Cart"),),
          body: cart.basketItems.length==0
          ?Text("no items"):ListView.builder(
            itemCount: cart.basketItems.length,
              itemBuilder: (context,index){
              return Card(
                child: ListTile(
                  title: Text(cart.basketItems[index].title),),);}),);},);}}

cartmodel.dart

class Item {
  String title;
  String image;
  double price;
  Item({this.title, this.price,this.image});}

Cart.dart

class Cart extends ChangeNotifier {
  List<Item> _items = [];
  double _totalPrice = 0.0;
  void add(Item item) {
    _items.add(item);
    _totalPrice += item.price;
    notifyListeners();}
  void remove(Item item) {
    _totalPrice -= item.price;
    _items.remove(item);
    notifyListeners();}
  int get count {
    return _items.length;}
  double get totalPrice {
    return _totalPrice;}
  List<Item> get basketItems {
    return _items;}}

Answer 1

出现此错误是因为您的add方法表单Cart类正在等待Item对象，并且您传递了productname这是一个字符串。

从您的代码中，您需要像这样在Item小部件中构建新的Quantities：

cart.add(Item(title: productname, image: productimage, price : productprice));

但是，如果您想改善代码，可以将Item类上的Quantities对象替换为这3个属性。您可以先将您的班级转换为StatelessWidget：

class Quantities extends StatelessWidget {
  final Item item;
  Quantities(this.item);
  @override
  Widget build() {
    ...

通常，您应该在可能的方法/小部件上使用该Item对象

Flutter中'String'类型不是'Item'类型的子类型

1 个答案: