小贝子编程

类型 'Null' 不是类型 'String' 映射到列表错误问题的子类型



我想列出来自API服务的json数据，并将其列在FutureBuilder上。但无论我做什么，它都会返回捕获。可能是什么问题？Json值即将到来，但我不能使用toList属性。我该怎么办？

支付服务：

Future<List<PaymentData>> paymentGetList() async {
SharedPreferences preferences = await SharedPreferences.getInstance();
// ignore: prefer_typing_uninitialized_variables
dynamic responseData;
String token = await getToken();
final paymentListApiUrl = Uri.parse(
apiUrlKey + preferences.getString('apiUrl').toString() + paymentListUrl);
try {
final response = await http.post(paymentListApiUrl, headers: {
'Authorization': token,
'Accept': 'application/json',
}, body: {
'filters': '',
'params': '',
'limit': '10',
'offset': '0',
'sorting': ''
});
if (response.statusCode == 200) {
var jsonData = jsonDecode(response.body);
var jsonArray = jsonData['data'];
List<PaymentData> jsonResult =
(jsonDecode(response.body)['data'] as List)
.map((e) => PaymentData.fromMap(e))
.toList();
responseData = jsonArray;
}
} catch (e) {
print("Error:  $e");
}
return responseData;
}

结果打印：flutter:错误：类型"Null"不是类型"String"的子类型

支付模型

PaymentData paymentDataFromMap(String str) =>
PaymentData.fromMap(json.decode(str));
String paymentDataToMap(PaymentData data) => json.encode(data.toMap());
class PaymentData {
PaymentData({
required this.id,
required this.paymentsendId,
required this.collectionEmail,
required this.collectionSms,
required this.periodOrder,
required this.email,
required this.cardType1,
required this.cardType2,
required this.cardNameSurname,
required this.comment,
required this.datumNull,
required this.customerId,
required this.orderid,
required this.installmentNumber,
required this.plusInstallment,
required this.status,
required this.maskedCard,
required this.totalWithCommison,
required this.totalWithoutCommison,
required this.currencyType,
required this.transactionData,
required this.transactionBank,
required this.transactionType,
required this.partial,
required this.nameSurname,
required this.phoneNumber,
required this.postCode,
required this.city,
required this.district,
required this.country,
required this.paymentType,
required this.memberCode,
required this.paymentNote,
required this.paymentAddress,
required this.erpOrderIds,
required this.erpStatus,
required this.erpStatusMsg,
required this.idNumber,
required this.taxNumber,
required this.paymentIp,
required this.space1,
required this.space2,
required this.space3,
required this.space4,
required this.space5,
required this.space6,
required this.space7,
required this.posId,
required this.createdIn,
required this.updatedIn,
});
final String id;
final String paymentsendId;
final String collectionEmail;
final String collectionSms;
final String periodOrder;
final String email;
final String cardType1;
final String cardType2;
final String cardNameSurname;
final String comment;
final String datumNull;
final String customerId;
final String orderid;
final String installmentNumber;
final String plusInstallment;
final String status;
final String maskedCard;
final String totalWithCommison;
final String totalWithoutCommison;
final String currencyType;
final String transactionData;
final String transactionBank;
final String transactionType;
final String partial;
final String nameSurname;
final String phoneNumber;
final String postCode;
final String city;
final String district;
final String country;
final String paymentType;
final String memberCode;
final String paymentNote;
final String paymentAddress;
final String erpOrderIds;
final String erpStatus;
final String erpStatusMsg;
final String idNumber;
final String taxNumber;
final String paymentIp;
final String space1;
final String space2;
final String space3;
final String space4;
final String space5;
final String space6;
final String space7;
final String posId;
final DateTime createdIn;
final DateTime updatedIn;
factory PaymentData.fromMap(Map<String, dynamic> json) => PaymentData(
id: json["id"],
paymentsendId: json["paymentsend_id"],
collectionEmail: json["collection_email"],
collectionSms: json["collection_sms"],
periodOrder: json["period_order"],
email: json["email"],
cardType1: json["card_type1"],
cardType2: json["card_type2"],
cardNameSurname: json["card_name_surname"],
comment: json["comment"],
datumNull: json["NULL"],
customerId: json["customer_id"],
orderid: json["orderid"],
installmentNumber: json["installment_number"],
plusInstallment: json["plus_installment"],
status: json["status"],
maskedCard: json["masked_card"],
totalWithCommison: json["total_with_commison"],
totalWithoutCommison: json["total_without_commison"],
currencyType: json["currency_type"],
transactionData: json["transaction_data"],
transactionBank: json["transaction_bank"],
transactionType: json["transaction_type"],
partial: json["partial"],
nameSurname: json["name_surname"],
phoneNumber: json["phone_number"],
postCode: json["post_code"],
city: json["city"],
district: json["district"],
country: json["country"],
paymentType: json["payment_type"],
memberCode: json["member_code"],
paymentNote: json["payment_note"],
paymentAddress: json["payment_address"],
erpOrderIds: json["erp_order_ids"],
erpStatus: json["erp_status"],
erpStatusMsg: json["erp_status_msg"],
idNumber: json["id_number"],
taxNumber: json["tax_number"],
paymentIp: json["payment_ip"],
space1: json["space1"],
space2: json["space2"],
space3: json["space3"],
space4: json["space4"],
space5: json["space5"],
space6: json["space6"],
space7: json["space7"],
posId: json["pos_id"],
createdIn: DateTime.parse(json["created_in"]),
updatedIn: DateTime.parse(json["updated_in"]),
);
factory PaymentData.fromJson(Map<String, dynamic> json) {
return PaymentData(
id: json["id"],
paymentsendId: json["paymentsend_id"],
collectionEmail: json["collection_email"],
collectionSms: json["collection_sms"],
periodOrder: json["period_order"],
email: json["email"],
cardType1: json["card_type1"],
cardType2: json["card_type2"],
cardNameSurname: json["card_name_surname"],
comment: json["comment"],
datumNull: json["NULL"],
customerId: json["customer_id"],
orderid: json["orderid"],
installmentNumber: json["installment_number"],
plusInstallment: json["plus_installment"],
status: json["status"],
maskedCard: json["masked_card"],
totalWithCommison: json["total_with_commison"],
totalWithoutCommison: json["total_without_commison"],
currencyType: json["currency_type"],
transactionData: json["transaction_data"],
transactionBank: json["transaction_bank"],
transactionType: json["transaction_type"],
partial: json["partial"],
nameSurname: json["name_surname"],
phoneNumber: json["phone_number"],
postCode: json["post_code"],
city: json["city"],
district: json["district"],
country: json["country"],
paymentType: json["payment_type"],
memberCode: json["member_code"],
paymentNote: json["payment_note"],
paymentAddress: json["payment_address"],
erpOrderIds: json["erp_order_ids"],
erpStatus: json["erp_status"],
erpStatusMsg: json["erp_status_msg"],
idNumber: json["id_number"],
taxNumber: json["tax_number"],
paymentIp: json["payment_ip"],
space1: json["space1"],
space2: json["space2"],
space3: json["space3"],
space4: json["space4"],
space5: json["space5"],
space6: json["space6"],
space7: json["space7"],
posId: json["pos_id"],
createdIn: DateTime.parse(json["created_in"]),
updatedIn: DateTime.parse(json["updated_in"]));
}
Map<String, dynamic> toMap() => {
"id": id,
"paymentsend_id": paymentsendId,
"collection_email": collectionEmail,
"collection_sms": collectionSms,
"period_order": periodOrder,
"email": email,
"card_type1": cardType1,
"card_type2": cardType2,
"card_name_surname": cardNameSurname,
"comment": comment,
"NULL": datumNull,
"customer_id": customerId,
"orderid": orderid,
"installment_number": installmentNumber,
"plus_installment": plusInstallment,
"status": status,
"masked_card": maskedCard,
"total_with_commison": totalWithCommison,
"total_without_commison": totalWithoutCommison,
"currency_type": currencyType,
"transaction_data": transactionData,
"transaction_bank": transactionBank,
"transaction_type": transactionType,
"partial": partial,
"name_surname": nameSurname,
"phone_number": phoneNumber,
"post_code": postCode,
"city": city,
"district": district,
"country": country,
"payment_type": paymentType,
"member_code": memberCode,
"payment_note": paymentNote,
"payment_address": paymentAddress,
"erp_order_ids": erpOrderIds,
"erp_status": erpStatus,
"erp_status_msg": erpStatusMsg,
"id_number": idNumber,
"tax_number": taxNumber,
"payment_ip": paymentIp,
"space1": space1,
"space2": space2,
"space3": space3,
"space4": space4,
"space5": space5,
"space6": space6,
"space7": space7,
"pos_id": posId,
"created_in": createdIn.toIso8601String(),
"updated_in": updatedIn.toIso8601String(),
};
}

当我在Payment_model.dart上打印时，我会得到以下结果。

[{id: 1, paymentsend_id: , collection_email: 0, collection_sms: 0, period_order: 0, email: mail@site.com, card_type1: cardfinans, card_type2: troy, card_name_surname: asktest, comment: , NULL: , customer_id: 123, orderid: 123123321, installment_number: 3, plus_installment: , status: 3D-POST, masked_card: 111111** **** 1111, total_with_commison: 1000.0000, total_without_commison: 1000.0000, currency_type: null, transaction_data: , transaction_bank: ing, transaction_type: 2, partial: , name_surname: asktest, phone_number: 1233123123, post_code: , city: Gaziantep, district: sahinbey, country: TR, payment_type: 3d, member_code: , payment_note: , payment_address: , erp_order_ids: , erp_status: , erp_status_msg: , id_number: , tax_number: , payment_ip: 111.111.11.11, space1: 12/2024, space2: , space3: , space4: log, space5: null, space6: null, space7: null, pos_id: null, created_in: 2021-11-26 12:54:07, updated_in: 0000-00-00 00:00:00}..]

您的JSON有一些NULL值。因此，让所有字段都不可为null不是一个好主意。若您确信"JSON的这个字段永远不会有null值"，那个么就让它不可为null。否则，这样更改它们：

final String? comment;
...

删除required

this.comment
...

您可以像这样更改PaymentModel.dart文件中的fromMap函数，以避免访问没有值的密钥

factory PaymentData.fromMap(Map<String, dynamic> json) => PaymentData(
id: json["id"] == null ? "" : json["id"],
paymentsendId: json["paymentsend_id"] == null ? "" : json["paymentsend_id"],
collectionEmail: json["collection_email"] == null ? "" : json["collection_email"],
collectionSms: json["collection_sms"] == null ? "" : json["collection_sms"],
periodOrder: json["period_order"] == null ? "" : json["period_order"],
email: json["email"] == null ? "" : json["email"],
cardType1: json["card_type1"] == null ? "" : json["card_type1"],
cardType2: json["card_type2"] == null ? "" : json["card_type2"],
cardNameSurname: json["card_name_surname"] == null ? "" : json["card_name_surname"],
comment: json["comment"] == null ? "" : json["comment"],
datumNull: json["NULL"] == null ? "" : json["NULL"],
customerId: json["customer_id"] == null ? "" : json["customer_id"],
orderid: json["orderid"] == null ? "" json["orderid"]: ,
installmentNumber: json["installment_number"] == null ? "" : json["installment_number"],
plusInstallment: json["plus_installment"] == null ? "" : json["plus_installment"],
status: json["status"] == null ? "" : json["status"],
maskedCard: json["masked_card"] == null ? "" : json["masked_card"],
totalWithCommison: json["total_with_commison"] == null ? "" : json["total_with_commison"],
totalWithoutCommison: json["total_without_commison"] == null ? "" : json["total_without_commison"],
currencyType: json["currency_type"] == null ? "" : json["currency_type"],
transactionData: json["transaction_data"] == null ? "" : json["transaction_data"],
transactionBank: json["transaction_bank"] == null ? "" : json["transaction_bank"],
transactionType: json["transaction_type"] == null ? "" : json["transaction_type"],
partial: json["partial"] == null ? "" : json["partial"],
nameSurname: json["name_surname"] == null ? "" : json["name_surname"],
phoneNumber: json["phone_number"] == null ? "" : json["phone_number"],
postCode: json["post_code"] == null ? "" : json["post_code"],
city: json["city"] == null ? "" : json["city"],
district: json["district"] == null ? "" : json["district"],
country: json["country"] == null ? "" : json["country"],
paymentType: json["payment_type"] == null ? "" : json["payment_type"],
memberCode: json["member_code"] == null ? "" : json["member_code"],
paymentNote: json["payment_note"] == null ? "" : json["payment_note"],
paymentAddress: json["payment_address"] == null ? "" : json["payment_address"],
erpOrderIds: json["erp_order_ids"] == null ? "" : json["erp_order_ids"],
erpStatus: json["erp_status"] == null ? "" : json["erp_status"],
erpStatusMsg: json["erp_status_msg"] == null ? "" : json["erp_status_msg"],
idNumber: json["id_number"] == null ? "" : json["id_number"],
taxNumber: json["tax_number"] == null ? "" : json["tax_number"],
paymentIp: json["payment_ip"] == null ? "" : json["payment_ip"],
space1: json["space1"] == null ? "" : json["space1"],
space2: json["space2"] == null ? "" : json["space2"],
space3: json["space3"] == null ? "" : json["space3"],
space4: json["space4"] == null ? "" : json["space4"],
space5: json["space5"] == null ? "" : json["space5"],
space6: json["space6"] == null ? "" : json["space6"],
space7: json["space7"] == null ? "" : json["space7"],
posId: json["pos_id"] == null ? "" : json["pos_id"],
createdIn: DateTime.parse(json["created_in"]),
updatedIn: DateTime.parse(json["updated_in"]),
);

并对fromJson功能执行相同操作

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