Flutter：从另一个 DateTime 列表生成每个月的总销售额列表

Question

我有一份每日销售清单，其中包括每个条目的“DateTime”和“Int”。

final data = [
      DailySales(2022-03-10 00:00:00.000, 200),
      DailySales(2022-03-09 00:00:00.000, 255),
      DailySales(2022-02-08 00:00:00.000, 100),
      DailySales(2022-02-10 00:00:00.000, 520),
      DailySales(2022-01-08 00:00:00.000, 100),
      DailySales(2022-01-10 00:00:00.000, 520),
    ];

class DailySales {
  final DateTime day;
  final int sales;

  DailySales(this.day, this.sales);
}

现在根据上面的列表，我需要动态生成一个新列表，其中应包含每个月份的名称和当月的总销售额。

如下模型所示：

class MonthlySales {
  final String month;
  final int sales;

  MonthlySales(this.month, this.sales);
}

请帮忙解决这个问题

Answer 1

你可以这样做：

main() {
  final data = [
    DailySales(DateTime.parse("2022-03-10 00:00:00.000"), 200),
    DailySales(DateTime.parse("2022-03-09 00:00:00.000"), 255),
    DailySales(DateTime.parse("2022-02-08 00:00:00.000"), 100),
    DailySales(DateTime.parse("2022-02-10 00:00:00.000"), 520),
    DailySales(DateTime.parse("2022-01-08 00:00:00.000"), 100),
    DailySales(DateTime.parse("2022-01-10 00:00:00.000"), 520),
  ];

  Map tempMap = Map();

  for (DailySales item in data) {
    if (tempMap[item.day.month] == null) {
      tempMap[item.day.month] = item.sales;
    } else {
      tempMap[item.day.month] = tempMap[item.day.month] + item.sales;
    }
  }
  List monthlySales = [];
  for (int i = 1; i <= 12; i++) {
    if (tempMap[i] != null)
      monthlySales.add(MonthlySales(i.toString(), tempMap[i]));
  }
  print(monthlySales);
}

class DailySales {
  final DateTime day;
  final int sales;

  DailySales(this.day, this.sales);
}

class MonthlySales {
  final String month;
  final int sales;

  MonthlySales(this.month, this.sales);
  @override
  String toString() {
    // TODO: implement toString
    return "month " + month + " sales " + sales.toString();
  }
}

输出看起来像：

[month 1 sales 620, month 2 sales 620, month 3 sales 455]

Answer 2

这是您需要做的：-

void main() {
  final data = [
    DailySales(day: DateTime(2022, 03, 09), sales: 200),
    DailySales(day: DateTime(2022, 03, 08), sales: 255),
    DailySales(day: DateTime(2022, 03, 07), sales: 100),
    DailySales(day: DateTime(2022, 03, 04), sales: 520),
    DailySales(day: DateTime(2022, 03, 02), sales: 100),
    DailySales(day: DateTime(2022, 03, 03), sales: 520),
  ];

  List<MonthlySales> monthlySales = data
      .map((dailySale) => MonthlySales(
          month: dailySale.day.month.toString(), sales: dailySale.sales))
      .toList();

  print(monthlySales.runtimeType);
  print(monthlySales.toString());
}

class DailySales {
  final DateTime day;
  final int sales;

  DailySales({required this.day, required this.sales});
}

class MonthlySales {
  final String month;
  final int sales;

  MonthlySales({required this.month, required this.sales});
}

输出如下：-

List<MonthlySales>
[Instance of 'MonthlySales', Instance of 'MonthlySales', Instance of 'MonthlySales', Instance of 'MonthlySales', Instance of 'MonthlySales', Instance of 'MonthlySales']

Dart 集合提供了很多这样丰富的方法，比如上面的 map 方法来简化业务逻辑。

一次访问 it 以获得更多帮助。

Answer 3

你可以使用这个包来分组数据collection

collection: ^1.15.0

 List<MonthlySales> OrderSalebymonth() {
  List<String> months = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];
  final datas = [DailySales(DateTime.parse("2022-03-10 00:00:00.000"), 200), DailySales(DateTime.parse("2022-03-09 00:00:00.000"), 255), DailySales(DateTime.parse("2022-02-08 00:00:00.000"), 100), DailySales(DateTime.parse("2022-02-10 00:00:00.000"), 520), DailySales(DateTime.parse("2022-01-08 00:00:00.000"), 100), DailySales(DateTime.parse("2022-01-10 00:00:00.000"), 520),];
  List<MonthlySales> monthlist = [];
  var groupBy2 = groupBy(datas, (DailySales sale) => sale.day.month);
  groupBy2.forEach((key, value) {print("=================Month:$key ${months[key - 1]}=============");value.forEach((element) {monthlist.add(MonthlySales(months[key - 1], element.sales));print(element.sales.toString());});});
  return monthlist;
}
class DailySales {
  final DateTime day;
  final int sales;

  DailySales(this.day, this.sales);
}

class MonthlySales {
  final String month;
  final int sales;

  MonthlySales(this.month, this.sales);
}

预期输出

=================Month:3 March=============
200
255
=================Month:2 February=============
100
520
=================Month:1 January=============
100
520

Flutter：从另一个 DateTime 列表生成每个月的总销售额列表

Flutter : Generate List of total sales for each month from another list of DateTime

list

dynamic-list

dart

flutter