如何在飞镖中生成像 {'day': day, 'amount': 0.0} 这样的地图列表

Question

从交易列表中生成列表

我有一个 dart 代码包含我要打印的交易列表 像 {'day': day, 'amount': 0.0} 的地图与交易列表中前三天的数据

    import 'package:intl/intl.dart';

class Transaction {
  final double amount;
  final DateTime date;

  Transaction({required this.amount, required this.date});
}

void main() {
  List<Transaction> transaction = [
    Transaction(
      amount: 100,
      date: DateTime.now().subtract(Duration(days: 2)),
    ),
    Transaction(
      amount: 200,
      date: DateTime.now().subtract(Duration(days: 1)),
    ),
    Transaction(
      amount: 100,
      date: DateTime.now(),
    ),
    Transaction(
      amount: 300,
      date: DateTime.now(),
    ),
    Transaction(
      amount: 100,
      date: DateTime.now(),
    ),
    Transaction(
      amount: 350,
      date: DateTime.now().subtract(Duration(days: 5)),
    ),
  ];


}

Answer 1

最简单的方法是在Transaction 上创建一个将Transaction 转换为Map<String, dynamic> 的方法：

class Transaction {
  final double amount;
  final DateTime date;

  Transaction({required this.amount, required this.date});

  Map<String, dynamic> toMap() => <String, dynamic>{
        'date': date,
        'amount': amount,
      };
}

然后您可以执行以下操作，先筛选出您要转换的交易，然后再进行转换：

  final datetimeNow = DateTime.now();
  List<Map<String, dynamic>> transactionsAsMaps = transactions
      .where(
          (transaction) => datetimeNow.difference(transaction.date).inDays <= 3)
      .map((transaction) => transaction.toMap())
      .toList();

一个完整的运行示例可以在这里找到：

class Transaction {
  final double amount;
  final DateTime date;

  Transaction({required this.amount, required this.date});

  Map<String, dynamic> toMap() => <String, dynamic>{
        'date': date,
        'amount': amount,
      };
}

void main() {
  List<Transaction> transactions = [
    Transaction(
      amount: 100,
      date: DateTime.now().subtract(Duration(days: 2)),
    ),
    Transaction(
      amount: 200,
      date: DateTime.now().subtract(Duration(days: 1)),
    ),
    Transaction(
      amount: 100,
      date: DateTime.now(),
    ),
    Transaction(
      amount: 300,
      date: DateTime.now(),
    ),
    Transaction(
      amount: 100,
      date: DateTime.now(),
    ),
    Transaction(
      amount: 350,
      date: DateTime.now().subtract(Duration(days: 5)),
    ),
  ];

  final datetimeNow = DateTime.now();
  List<Map<String, dynamic>> transactionsAsMaps = transactions
      .where(
          (transaction) => datetimeNow.difference(transaction.date).inDays <= 3)
      .map((transaction) => transaction.toMap())
      .toList();

  transactionsAsMaps.forEach(print);
  // {date: 2022-01-08 15:56:24.924579, amount: 100.0}
  // {date: 2022-01-09 15:56:24.924579, amount: 200.0}
  // {date: 2022-01-10 15:56:24.924579, amount: 100.0}
  // {date: 2022-01-10 15:56:24.924579, amount: 300.0}
  // {date: 2022-01-10 15:56:24.924579, amount: 100.0}
}