我在处理 Flutter 时遇到问题。 请帮我

Question

参数类型“对象？” 不能分配给参数类型“字符串”。dartargument_type_not_assignable code粗斜体

class Category{
  final String name;
  final int numOfCoure;
  final String image;

  Category(this.name, this.numOfCoure, this.image);
}

var categoriesData = [
  {"name":"Lúa", 'course': 17, 'image' :"data\\images\\lua.png"},
  {"name":"Ngô", 'course': 25, 'image' :"data\\images\\ngo.png"},
  {"name":"Rau", 'course': 13, 'image' :"data\\images\\rau.png"},
  {"name":"Hoa", 'course': 17, 'image' :"data\\images\\hoa.png"},
];


List<Category> categories = categoriesData
    .map((item) => Category(item['name'], item['course'], item['image']))
    .toList();

Answer 1

使用命名参数，它将解决您的问题。

class Category{
  final String? name;
  final int? numOfCoure;
  final String? image;

  Category({this.name, this.numOfCoure, this.image});
}

var categoriesData = [
  {"name":"Lúa", 'course': 17, 'image' :"data\\images\\lua.png"},
  {"name":"Ngô", 'course': 25, 'image' :"data\\images\\ngo.png"},
  {"name":"Rau", 'course': 13, 'image' :"data\\images\\rau.png"},
  {"name":"Hoa", 'course': 17, 'image' :"data\\images\\hoa.png"},
];


List<Category> categories = categoriesData
    .map((item) => Category(
        name: item['name'], 
        numOfCoure: item['course'], 
        image: item['image'],
    ))
    .toList();

确保在类别 class 中声明的字段前面添加可空字符，因为您尚未在构造函数中初始化它们。

Answer 2

尝试给它一个类型

class Category{
  final String name;
  final int numOfCoure;
  final String image;

  Category(this.name, this.numOfCoure, this.image);
}

var categoriesData = [
  {"name":"Lúa", 'course': 17, 'image' :"data\\images\\lua.png"},
  {"name":"Ngô", 'course': 25, 'image' :"data\\images\\ngo.png"},
  {"name":"Rau", 'course': 13, 'image' :"data\\images\\rau.png"},
  {"name":"Hoa", 'course': 17, 'image' :"data\\images\\hoa.png"},
];


List<Category> categories = categoriesData
    .map((item) => Category(item['name'] as String, item['course'] as int, item['image'] as String))
    .toList();