Question

我使用以下代码打印列表

 print(snapshot.data.toList().toString());

，这里是输出[ABC(oid: 343, id: 138), ABC(oid: 344, id: 139),ABC(oid:345,id:138)]

我尝试使用软件包collection根据ID对列表进行分组：

 var _reading = snapshot.data[index];
 var newMap = groupBy(snapshot.data.toList(),
                          (obj) => obj[_reading.id]);

错误

类'ABC'没有实例方法'[]'。接收方：“ ABC”实例尝试调用：[](12)

Answer 1

也许这个简单的例子对您有帮助？

import 'package:enumerable/enumerable.dart';

void main() {
  final query = data.groupBy((e) => e.id);
  print(query);
  print(query.toMap((e) => e.key));
  for (final element in query) {
    print('key: ${element.key}');
    for (var value in element) {
      print('  $value');
    }
  }
}

final data = [
  ABC(oid: 343, id: 138),
  ABC(oid: 344, id: 139),
  ABC(oid: 345, id: 138)
];

class ABC {
  int id;
  int oid;

  @override
  String toString() {
    return 'ABC <oid: $oid, id: $id>';
  }

  ABC({this.id, this.oid});
}

结果：

((ABC <oid: 343, id: 138>, ABC <oid: 345, id: 138>), (ABC <oid: 344, id: 139>)) {138: (ABC <oid: 343, id: 138>, ABC <oid: 345, id: 138>), 139: (ABC <oid: 344, id: 139>)} key: 138 ABC <oid: 343, id: 138> ABC <oid: 345, id: 138> key: 139 ABC <oid: 344, id: 139>

在颤抖中列出组

1 个答案: