Flutter开发遇Set未定义/运算符等3个Dart类型报错如何解决

错误1：参数类型'Object?'无法分配给参数类型'num' #

报错行：return sum + item['amount'];
修复：你定义的groupedTransactionValues是List<Map<String, Object>>类型，从Map中取出的值默认是Object?类型，需要显式强转为double：

return sum + (item['amount'] as double);

错误2：类型'Set'未定义运算符'/' #

报错行：{data['amount'] as double} / totalSpending);
修复：你错误使用大括号包裹了类型转换代码，Dart中大括号包裹单个值会被识别为Set集合，自然没有除法运算符，改成小括号包裹即可：

(data['amount'] as double) / totalSpending

错误3：参数类型'Object?'无法分配给参数类型'double' #

报错行：data['amount'];
修复：直接强转为double类型即可，不要用double.parse，double.parse仅支持字符串入参，你这里data['amount']本身存储的就是double类型，不需要转字符串再解析：

data['amount'] as double

完整修改后代码 #

import 'package:expense_app/Widget/chart_bar.dart';
import 'package:expense_app/models/transaction.dart';
import 'package:flutter/material.dart';
import 'package:intl/intl.dart';

class Chart extends StatelessWidget {
  final List<Transaction> recentTransactions;

  Chart(this.recentTransactions);

  List<Map<String, Object>> get groupedTransactionValues {
    return List.generate(7, (index) {
      final weekDay = DateTime.now().subtract(
        Duration(days: index),
      );
      var totalSum = 0.0;
      for (var i = 0; i < recentTransactions.length; i++) {
        if (recentTransactions[i].date.day == weekDay.day &&
            recentTransactions[i].date.month == weekDay.month &&
            recentTransactions[i].date.year == weekDay.year) {
          totalSum += recentTransactions[i].amount;
        }
      }

      return {
        'day': DateFormat.E().format(weekDay).substring(0, 1),
        'amount': totalSum,
      };
    }).reversed.toList();
  }

  double get totalSpending {
    return groupedTransactionValues.fold(0.0, (sum, item) {
      // 修复错误1：添加显式类型转换
      return sum + (item['amount'] as double);
    });
  }

  @override
  Widget build(BuildContext context) {
    print(groupedTransactionValues);
    return Card(
      elevation: 6,
      margin: EdgeInsets.all(20),
      child: Container(
        padding: EdgeInsets.all(10),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceAround,
          children: groupedTransactionValues.map((data) {
            return Flexible(
              fit: FlexFit.tight,
              child: Chartbar(
                  data['day'].toString(),
                  // 修复错误3：显式转double
                  data['amount'] as double,
                  totalSpending == 0.0
                      ? 0.0
                      // 修复错误2：替换大括号为小括号
                      : (data['amount'] as double) / totalSpending),
            );
          }).toList(),
        ),
      ),
    );
  }
}

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