参数类型 'List<String>' 不能分配给 Dart 上的参数类型 'String'.dart(argument_type_not_assignable)答案

【问题标题】：The argument type 'List<String>' can't be assigned to the parameter type 'String'.dart(argument_type_not_assignable) on the Dart参数类型 'List<String>' 不能分配给 Dart 上的参数类型 'String'.dart(argument_type_not_assignable)
【发布时间】：2021-06-06 11:31:48
【问题描述】：

“字符串？”类型的值不能分配给“字符串”类型的变量。尝试更改变量的类型，或将右侧类型转换为 'String'.dart(invalid_assignment)

  late String manufacturer;
  late double fuelCapacity;
  late double fuelRemaining;

  String showInfo() =>
      '$manufacturer: $fuelRemaining of $fuelCapacity (critical: $criticalFuelLevel)';

  double get criticalFuelLevel => fuelCapacity * 0.1;
  set newFuelRemaining(double val) => fuelRemaining = val;

  // default constructor
  Vehicle(
      {required this.manufacturer,
      required this.fuelCapacity,
      required this.fuelRemaining});

  // named constructor
  Vehicle.fromMap(Map<String,String> map) {
    this.manufacturer = map["manufacturer"];
    this.fuelCapacity = double.parse(["fuelCapacity"]);
    this.fuelRemaining = double.parse(['fuelRemaining']);
  }
}

void main() {
  var vehicle =
      Vehicle(manufacturer: 'BMW', fuelCapacity: 55, fuelRemaining: 20);

  vehicle.newFuelRemaining = 20;

  var vehicle2 = Vehicle.fromMap(
      {'manufacturer': 'KIA', 'fuelCapacity': '50', 'fuelRemaining': '20'});

  print(vehicle2.showInfo());
}```

【问题讨论】：

标签： flutter

【解决方案1】：

这是因为map["manufacturer"]; 无法确定制造商是否在地图内。如果它确定在那里，你可以告诉 Dart 它不能像那样为空（最后是 !）：

 this.manufacturer = map["manufacturer"]!;

如果您还需要什么或者问题不存在，请告诉我:)

【讨论】：