I have a problem with object handling in Flutter-CodePudding

Error:

The argument type 'Object?' can't be assigned to the parameter type 'String'.dartargument_type_not_assignable

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();

CodePudding user response：

Use named parameter and it will solve your problem.

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();

Make sure to add nullable character in front of the field declared in Category class as you haven't initialized them in constructor.

CodePudding user response：

Try giving it a type

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();