如何访问 Dart 中嵌套映射中给定键的值？

Question

我是 Dart 的新手，我一直在尝试访问以下代码中“farm_size”键的值，但没有成功。我最多可以访问这样的“农场”

print(myData1[0]["farms"]);

但没有进一步。任何帮助将不胜感激。谢谢

void main() {
  var myData1 = [
  {
    "id": 1,
    "first_name": "Jordan",
    "sur_name": "Zamunda",
    "member_n0": "AA1",
    "gender": "male",
    "phone": "123456789",
    "email": "jordan@example.com",
    "farms": [
      {"id": 1, "farm_name": "SOUTH_FARM", "farm_size": "160 acres"},
      {"id": 2, "farm_name": "NORTH_FARM", "farm_size": "190 acres"}
    ]
  }
];

  print(myData1[0]["farms"]);

}

Answer 1

在farms里面，有一个更多地图的列表，要访问这些地图，你需要指定你的地图的索引，比如我们要获取第一张地图，我们输入：

print(myData1[0]["farms"][0]);
//this will print => {"id": 1, "farm_name": "SOUTH_FARM", "farm_size": "160 acres"}

//to get the name of this farm, you use the key 'farm_name' now:
print(myData1[0]["farms"][0]['farm_name']);
//prints=> SOUTH_FARM

如果你在 dartpad 中运行它，这将起作用：

void main() {
  
  var myData1 = [
  {
    "id": 1,
    "first_name": "Jordan",
    "sur_name": "Zamunda",
    "member_n0": "AA1",
    "gender": "male",
    "phone": "123456789",
    "email": "jordan@example.com",
    "farms": [
      {"id": 1, "farm_name": "SOUTH_FARM", "farm_size": "160 acres"},
      {"id": 2, "farm_name": "NORTH_FARM", "farm_size": "190 acres"}
    ]
  }
];
  List<Map<String,dynamic>> _list = myData1[0]["farms"]as List<Map<String,dynamic>> ;
  
  print(_list[0]['farm_name']);


}

Answer 2

试试这个

List m = myData1[0]['farms'] as List;

 print(m[0]['id']);

如何访问 Dart 中嵌套映射中给定键的值？

How do I access the value of a given key in a nested Map in Dart?

dart

flutter

dart-null-safety