Flutter：如何将API交易数据按月份去重并汇总对应金额

需求说明 #

原始API返回的交易数据：

[
 {"type": "expense", "amount": 250, "paymentDate": "22-02-2022"},
 {"type": "income", "amount": 350, "paymentDate": "22-02-2022"},
 {"type": "expense", "amount": 150, "paymentDate": "22-02-2022"},
 {"type": "expense", "amount": 450, "paymentDate": "22-03-2022"},
 {"type": "income", "amount": 650, "paymentDate": "22-03-2022"},
 {"type": "expense", "amount": 650, "paymentDate": "22-05-2022"},
 {"type": "income", "amount": 650, "paymentDate": "22-05-2022"},
 {"type": "income", "amount": 650, "paymentDate": "22-05-2022"}
]

需要将同一月份的所有交易金额汇总，生成如下格式的列表：

[
  {"x": 2, "y": 750},
  {"x": 3, "y": 1100},
  {"x": 5, "y": 1950}
]

实现步骤 #

1. 添加依赖

确保pubspec.yaml中引入intl包（用于日期解析）：

dependencies:
  flutter:
    sdk: flutter
  intl: ^0.18.1

执行flutter pub get完成依赖安装。

2. 定义数据模型

创建交易数据模型类，简化数据处理流程：

class Transaction {
  final String type;
  final int amount;
  final String paymentDate;

  Transaction({
    required this.type,
    required this.amount,
    required this.paymentDate,
  });

  // 从JSON转换为模型实例
  factory Transaction.fromJson(Map<String, dynamic> json) {
    return Transaction(
      type: json['type'],
      amount: json['amount'],
      paymentDate: json['paymentDate'],
    );
  }
}

3. 实现汇总逻辑

核心逻辑是按月份分组累加金额，代码如下：

import 'package:intl/intl.dart';

List<Map<String, int>> aggregateTransactionsByMonth(List<Transaction> transactions) {
  // 用Map存储月份对应的总金额，key为月份int，value为总金额
  final Map<int, int> monthlyTotal = {};

  for (final transaction in transactions) {
    // 解析日期，提取月份
    final dateFormat = DateFormat('dd-MM-yyyy');
    final date = dateFormat.parse(transaction.paymentDate);
    final month = date.month;

    // 累加金额到对应月份
    if (monthlyTotal.containsKey(month)) {
      monthlyTotal[month] = monthlyTotal[month]! + transaction.amount;
    } else {
      monthlyTotal[month] = transaction.amount;
    }
  }

  // 将Map转换为目标格式的列表
  return monthlyTotal.entries.map((entry) {
    return {"x": entry.key, "y": entry.value};
  }).toList();
}

4. 完整使用示例

void main() {
  // 模拟API返回的原始数据
  final rawTransactions = [
    {"type": "expense", "amount": 250, "paymentDate": "22-02-2022"},
    {"type": "income", "amount": 350, "paymentDate": "22-02-2022"},
    {"type": "expense", "amount": 150, "paymentDate": "22-02-2022"},
    {"type": "expense", "amount": 450, "paymentDate": "22-03-2022"},
    {"type": "income", "amount": 650, "paymentDate": "22-03-2022"},
    {"type": "expense", "amount": 650, "paymentDate": "22-05-2022"},
    {"type": "income", "amount": 650, "paymentDate": "22-05-2022"},
    {"type": "income", "amount": 650, "paymentDate": "22-05-2022"}
  ];

  // 转换为模型列表
  final transactions = rawTransactions.map((json) => Transaction.fromJson(json)).toList();

  // 执行汇总
  final result = aggregateTransactionsByMonth(transactions);

  // 打印结果
  print(result);
  // 输出: [{"x":2, "y":750}, {"x":3, "y":1100}, {"x":5, "y":1950}]
}

关键说明 #

• 日期解析：使用intl包的DateFormat匹配原始日期的dd-MM-yyyy格式，确保准确提取月份。
• 分组累加：通过Map作为中间容器，快速定位对应月份并累加金额，处理效率较高。
• 格式转换：最后将Map键值对转换为目标要求的列表结构，直接满足输出需求。

内容的提问来源于stack exchange，提问作者user3352042