列表<map<string,dynamic> &gt; 列出<string> Dart </string></map<string,dynamic>

Question

I am new to programming. I have a List<Map<String,dynamic>> of data and I want to create a List of Strings from map values. Here is my sample data. Let's say I need a list of product names in Dart. Appreciate your help.Thanks.

final products = [  
     {'productimage': 'image1.jpg', 'productprice': '800', 'productid': '1234', 'productname': 'rabbittoy'},
     {'productimage': 'image2.jpg', 'productprice': '400', 'productid': 'p10001', 'productname': 'mousetoy'},
     {'productid': '4533', 'productprice': '1800', 'productimage': 'image3.jpg', 'productname': 'cat'},
     {'productname': 'dog', 'productid': 'p10002', 'productimage': 'image4.jpg', 'productprice': '3000'}
];

Answer 1

If your list was assigned to a variable called products I would use .map() to do the following:

final productNames = products.map((Map<String, dynamic> product) {
  return product["productname"];
}).toList();

I'm using .toList() at the end because .map() returns an Iterable object rather than a List object. I couldn't give you a 100% answer on why but you can read about it here .

Answer 2

You could use the fold method:

  List<String> productNames = data.fold<List<String>>(
      [], (prev, element) => List.from(prev)..add(element['productname']));

Full snippet example:

void main() {
  List<Map<String, dynamic>> data = [
    {
      'productimage': 'image1.jpg',
      'productprice': '800',
      'productid': '1234',
      'productname': 'rabbittoy'
    },
    {
      'productimage': 'image2.jpg',
      'productprice': '400',
      'productid': 'p10001',
      'productname': 'mousetoy'
    },
    {
      'productid': '4533',
      'productprice': '1800',
      'productimage': 'image3.jpg',
      'productname': 'cat'
    },
    {
      'productname': 'dog',
      'productid': 'p10002',
      'productimage': 'image4.jpg',
      'productprice': '3000'
    }
  ];

  List<String> productNames = data.fold<List<String>>(
      [], (prev, element) => List.from(prev)..add(element['productname']));
  print(productNames); // [rabbittoy, mousetoy, cat, dog]
}