错误：键入 '() => Map<string, dynamic> ？' 不是类型“Map”的子类型<string, dynamic> ？'</string,></string,>

Question

我正在尝试获取条形码来扫描项目并从 Cloud firestore 数据库中检索项目。 该应用程序旨在随后将项目显示在主页上。 但我一直有同样的错误。 我试图将其更改为 Map<Dynamic, Dynamic>。 我还尝试将其从不是 null Map<String, dynamic> 没有问号中删除。 所有 flutter 库以及 pubspec 都是最新的。

下面的代码是我的主页

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/services.dart';
import 'package:flutter_barcode_scanner/flutter_barcode_scanner.dart';

  Map<String, dynamic>? mapProducts = {};

  //Initialize
  @override
  void initState() {
    if (userProfile.containsKey("Unordered Products")) {
      mapProducts = userProfile["Unordered Products"];
    }

    super.initState();
  }

  @override
  void dispose() {
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    double size =
        MediaQuery.of(context).size.width < MediaQuery.of(context).size.height
            ? MediaQuery.of(context).size.width
            : (!kIsWeb)
                ? MediaQuery.of(context).size.height
                : MediaQuery.of(context).size.height / 2;

    //For Refreshing the theme
    if (userProfile.containsKey("Theme")) {
      myAppTheme = userProfile["Theme"] == "Light Theme"
          ? getMainThemeWithBrightness(context, Brightness.light)
          : getMainThemeWithBrightness(context, Brightness.dark);
    }

    MobileScannerController cameraController = MobileScannerController();

    return SafeArea(
      child: Scaffold(
        key: scaffoldKey,
        backgroundColor: myAppTheme?.scaffoldBackgroundColor,
        appBar: getAppBar(
          scaffoldKey: scaffoldKey,
          context: context,
          strAppBarTitle: "Spar Store",
          showBackButton: false,
        ),

        //drawer
        drawer: getDrawer(context, scaffoldKey),

        floatingActionButton: FloatingActionButton(
          backgroundColor: myAppTheme?.primaryColor,
          onPressed: () async {
            String? barcode = await scan();
            if (barcode != null && barcode != "") {
              if (mapProducts!.containsKey(barcode)) {
                //Increase count
                setState(() {
                  mapProducts![barcode] = ++mapProducts![barcode];
                });
              } else {
                //Add a new product
                setState(() {
                  mapProducts![barcode] = 1;
                });
              }
              userProfile["Unordered Products"] = mapProducts;

              //Update the new Unordered Products list to the Firebase CLoud Firestpre
              await authService.setData();
            }
          },
          child: Icon(Icons.add, color: myAppTheme?.iconTheme.color),
        ),

        //Body
        body: mapProducts != null && mapProducts!.length > 0
            ? Column(
                children: <Widget>[
                  //Products in Cart List
                  getUnorderedProducts(size),

                  //Final invoice
                  getInvoice(size),

                  //Checkout Button
                  getCheckoutButton(size),
                ],
              )
            : Center(
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Image.asset(
                      "assets/images/empty-cart.png",
                      fit: BoxFit.fitWidth,
                    ),
                    Text(
                      "No Items Added.\nPlease Add items by scanning them",
                      style: myAppTheme?.textTheme.caption,
                      textAlign: TextAlign.center,
                    ),
                  ],
                ),
              ),
      ),
    );
  }

  //Get the list of all the Orders still in Cart
  getUnorderedProducts(double size) {
    return SizedBox(
      width: MediaQuery.of(context).size.width,
      height: MediaQuery.of(context).size.height * 0.7,
      child: ListView.builder(
          itemCount: mapProducts!.length,
          itemBuilder: (context, index) {
            return FutureBuilder(
              builder: (BuildContext context, AsyncSnapshot snapshot) {
                if (snapshot.data == null || snapshot.hasData == false) {
                  return Center(
                    child: CircularProgressIndicator(
                      valueColor: AlwaysStoppedAnimation<Color>(
                          myAppTheme!.primaryColor),
                      strokeWidth: 5,
                    ),
                  );
                } else {
                  Map<String, dynamic>? mapProduct = snapshot.data;

                  return GestureDetector(
                    child: Card(
                      elevation: myAppTheme?.cardTheme.elevation,
                      color: myAppTheme?.cardTheme.color,
                      shape: myAppTheme?.cardTheme.shape,
                      child: Row(
                        children: <Widget>[
                          mapProduct!.containsKey("photo url")
                              ? ClipRRect(
                                  borderRadius: BorderRadius.circular(15),
                                  child: SizedBox(
                                      width: 120,
                                      child: Image.network(
                                          mapProduct["photo url"][0])))
                              : Icon(
                                  Icons.category,
                                  color: myAppTheme?.iconTheme.color,
                                ),
                          SizedBox(
                            width: size - 150,
                            child: Column(
                              crossAxisAlignment: CrossAxisAlignment.end,
                              children: <Widget>[
                                //Title
                                Padding(
                                  padding: const EdgeInsets.all(8.0),
                                  child: Text(
                                    mapProduct["name"],
                                    style: myAppTheme?.textTheme.caption,
                                    overflow: TextOverflow.ellipsis,
                                    textAlign: TextAlign.right,
                                  ),
                                ),

                                //Model
                                Padding(
                                  padding: const EdgeInsets.all(8.0),
                                  child: Text(mapProduct["model"],
                                      style: myAppTheme?.textTheme.bodyText1,
                                      overflow: TextOverflow.ellipsis,
                                      textAlign: TextAlign.right),
                                ),

                                //Discount
                                Padding(
                                  padding: const EdgeInsets.all(8.0),
                                  child: Text(
                                      "Discount: ${mapProduct["discount"]}%",
                                      style: myAppTheme?.textTheme.bodyText1
                                          ?.copyWith(
                                              fontWeight: FontWeight.bold),
                                      overflow: TextOverflow.ellipsis,
                                      textAlign: TextAlign.right),
                                ),

                                //Price
                                Padding(
                                  padding: const EdgeInsets.all(8.0),
                                  child: Text("Price: ${mapProduct["price"]}",
                                      style: myAppTheme?.textTheme.bodyText1
                                          ?.copyWith(
                                              fontWeight: FontWeight.bold),
                                      overflow: TextOverflow.ellipsis,
                                      textAlign: TextAlign.right),
                                ),

                                //Quantity
                                Container(
                                  padding: const EdgeInsets.all(8.0),
                                  height: 60,
                                  child: StepperTouch(
                                    initialValue:
                                        mapProducts?.values.elementAt(index),
                                    direction: Axis.horizontal,
                                    withSpring: true,
                                    primaryColor:
                                        myAppTheme?.colorScheme.secondary,
                                    textColor:
                                        myAppTheme?.textTheme.bodyText1?.color,
                                    onChanged: (int value) {
                                      if (value == 0) {
                                        setState(() {
                                          mapProducts?.remove(mapProducts?.keys
                                              .elementAt(index));
                                        });
                                      } else if (value > 0) {
                                        setState(() {
                                          mapProducts![mapProducts!.keys
                                              .elementAt(index)] = value;
                                        });
                                      }

                                      userProfile["Unordered Products"] =
                                          mapProducts;
                                    },
                                  ),
                                ),
                              ],
                            ),
                          ),
                        ],
                      ),
                    ),

                    //Open
                    onTap: () {
                      Navigator.push(
                        context,
                        MaterialPageRoute(
                            builder: (context) =>
                                ViewProductScreen(mapProduct)),
                      );
                    },
                  );
                }
              },
              future: getProduct(mapProducts!.keys.elementAt(index)),
            );
          }),
    );
  }

  //Get the Total Price and the Total discount
  getInvoice(double size) {
    return FutureBuilder(
      builder: (BuildContext context, AsyncSnapshot snapshot) {
        if (snapshot == null ||
            snapshot.data == null ||
            snapshot.hasData == false) {
          return Center(
            child: CircularProgressIndicator(
              valueColor:
                  AlwaysStoppedAnimation<Color>(myAppTheme!.primaryColor),
              strokeWidth: 5,
            ),
          );
        } else {
          Map mapProduct = snapshot.data;

          double dbTotalDiscount = mapProduct["discount"],
              dbTotalPrice = mapProduct["price"];

          return Column(
            crossAxisAlignment: CrossAxisAlignment.end,
            children: <Widget>[
              
              //Total Price
              Padding(
                padding: const EdgeInsets.fromLTRB(0, 5, 10, 5),
                child: Row(
                  mainAxisAlignment: MainAxisAlignment.end,
                  children: <Widget>[
                    Text(
                      "Total Price:   ",
                      style: myAppTheme?.textTheme.bodyText1,
                      overflow: TextOverflow.ellipsis,
                    ),
                    Text(
                      dbTotalPrice.toString(),
                      style: myAppTheme?.textTheme.bodyText1,
                      overflow: TextOverflow.ellipsis,
                    ),
                  ],
                ),
              ),
            ],
          );
        }
      },
      future: getInvoiceDetails(),
    );
  }

  getInvoiceDetails() async {
    double dbTotalDiscount = 0.0, dbTotalPrice = 0.0;

    //Loop through all the products to get the Discount and the Price
    await Future.forEach(mapProducts!.keys, (key) async {
      String strProductID = key;
      Map<String, dynamic>? mapProduct =
          (await getProduct(strProductID)) as Map<String, dynamic>?;

      if (mapProduct!.containsKey("discount")) {
        dbTotalDiscount += double.tryParse(
            (mapProduct["discount"] * mapProducts![key]).toString())!;
      }
      if (mapProduct.containsKey("price")) {
        dbTotalPrice += double.tryParse(
            (mapProduct["price"] * mapProducts![key]).toString())!;
      }
//      print("discount: " + dbTotalDiscount.toString());
//      print("price: " + dbTotalPrice.toString());
    });

    return {"discount": dbTotalDiscount, "price": dbTotalPrice};
  }

  //Get Checkout button
  getCheckoutButton(double size) {
    return ButtonTheme(
      minWidth: double.infinity,
      child: Padding(
        padding: const EdgeInsets.fromLTRB(80, 20, 80, 10),
        child: primaryRaisedButton(
          context: context,
          text: "Checkout now",
          color: myAppTheme?.primaryColor,
          onPressed: () async {
            //Go to Checkout
            await Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => CheckoutScreen()),
            );

            setState(() {
              //Refresh the UI after returning back from the Checkout screen
              mapProducts = userProfile["Unordered Products"];
            });
          },
        ),
      ),
    );
  }

  //=================================================================================
  //Get details of product
  Future<Map<String, dynamic>? Function()> getProduct(String barcode) async {
    return (await FirebaseFirestore.instance
            .collection("Products")
            .doc(barcode)
            .get())
        .data;
  }

  //Scan QR code
  Future<String?> scan() async {
    try {
      String barcode = (await FlutterBarcodeScanner.scanBarcode(
          '#ff6666', 'Cancel', true, ScanMode.QR));
      return barcode;
    } on PlatformException catch (e) {
      if (e.code == BarcodeScanner.cameraAccessDenied) {
        showSnackBar(
            scaffoldKey: scaffoldKey,
            text: "The user did not grant the camera permission!",
            buttonText: '',
            onPressed: () {});
      } else {
        showSnackBar(
            scaffoldKey: scaffoldKey,
            text: "Unknown error: $e",
            buttonText: '',
            onPressed: () {});
      }

      return null;
    } on FormatException {
      showSnackBar(
          scaffoldKey: scaffoldKey,
          text:
              'null (User returned using the "back"-button before scanning anything. Result)',
          buttonText: '',
          onPressed: () {});
    } catch (e) {
      showSnackBar(
          scaffoldKey: scaffoldKey,
          text: "Unknown error: $e",
          buttonText: '',
          onPressed: () {});
    }
    return null;
  }
}

如果有人能提供帮助会很棒，因为我是初学者，而且是针对学校项目的。

Answer 1

用这个替换你的getProduct()方法：

 Future<Map<String, dynamic>?> getProduct(String barcode) async {
    return (await FirebaseFirestore.instance
            .collection("Products")
            .doc(barcode)
            .get())
        .data() ;
  }