Flutter开发Dart报错：参数类型Object?无法赋值给String/int类型如何解决

• 你定义的cardData默认泛型为List<Map<String, Object?>>，通过item['xxx']读取到的值是可空的Object类型，无法直接赋值给CardModel构造函数要求的非空String/int类型，因此触发类型不匹配报错。
• 额外注意：你当前代码中cards的初始化声明在cardData之前，还会触发变量未初始化的报错，需要调整两者的先后顺序。

方案1：显式声明类型+强制类型转换（适合静态固定的测试数据） #

显式指定Map的value类型，同时对每个取值做明确的类型转换即可，修改后代码如下：

// 先声明cardData
var cardData = <Map<String, dynamic>>[
  {
    "user": "Berfin Gürz",
    "cardNumber": "**** **** **** 1727",
    "cardExpired": "17-01-2022",
    "cardType": "assets/images/mastercard_logo.png",
    "cardBackground": 0xFF1E1E99,
    "cardElementTop": "assets/svg/ellipse_top_pink.svg",
    "cardElementBottom": "assets/svg/ellipse_bottom_pink.svg"
  },
  {
    "user": "Berfin Gürz",
    "cardNumber": "**** **** **** 8213",
    "cardExpired": "03-01-2024",
    "cardType": "assets/images/mastercard_logo.png",
    "cardBackground": 0xFFFF70A3,
    "cardElementTop": "assets/svg/ellipse_top_blue.svg",
    "cardElementBottom": "assets/svg/ellipse_bottom_blue.svg"
  }
];

List<CardModel> cards = cardData.map(
  (item) => CardModel(
    item['user'] as String,
    item['cardNumber'] as String,
    item['cardExpired'] as String,
    item['cardType'] as String,
    item['cardBackground'] as int,
    item['cardElementTop'] as String,
    item['cardElementBottom'] as String,
  ),
).toList();

class CardModel {
  String user;
  String cardNumber;
  String cardExpired;
  String cardType;
  int cardBackground;
  String cardElementTop;
  String cardElementBottom;

  CardModel(this.user, this.cardNumber, this.cardExpired, this.cardType,
      this.cardBackground, this.cardElementTop, this.cardElementBottom);
}

方案2：增加空安全校验（适合后端接口返回的动态数据） #

如果数据来源是动态接口，不能保证字段一定存在或类型正确，可以增加兜底逻辑避免运行崩溃：

List<CardModel> cards = cardData.map(
  (item) => CardModel(
    item['user']?.toString() ?? '',
    item['cardNumber']?.toString() ?? '',
    item['cardExpired']?.toString() ?? '',
    item['cardType']?.toString() ?? '',
    item['cardBackground'] as int? ?? 0,
    item['cardElementTop']?.toString() ?? '',
    item['cardElementBottom']?.toString() ?? '',
  ),
).toList();

内容的提问来源于stack exchange，提问作者MaybeExpertDBA