Flutter JSON解析错误：List无法转为Map<String, dynamic>求助

核心问题有两个：

• JSON中的test是数组（List），但你代码里将其当作单个Map解析，且test字段定义为单个MonthWiseTests对象，类型完全不匹配
• MonthWiseTests.fromJson的写法错误，它当前逻辑是取Map的第一个key作为month，但JSON里每个test项是明确包含month和tests字段的Map

以下是完整修正方案：

1. 修正TestHistoryEntity的字段与解析逻辑 #

将test字段从单个对象改为列表，同时遍历JSON数组生成对应对象列表：

class TestHistoryEntity {
  TestHistoryEntity({this.subjects, this.test, this.filter1});

  TestHistoryEntity.fromJson(Map<String, dynamic> json) {
    if (json['subjects'] != null) {
      subjects = <Subjects>[];
      (json['subjects'] as List).forEach((v) {
        subjects!.add(Subjects.fromJson(v as Map<String, dynamic>));
      });
    }
    if (json['filter1'] != null) {
      filter1 = <String>[];
      (json['filter1'] as List).forEach((v) {
        filter1!.add(v.toString());
      });
    }
    if (kDebugMode) {
      print("FILTER_TEST");
      print(filter1);
    }

    // 修复test数组解析逻辑
    if (json['test'] != null) {
      test = <MonthWiseTests>[];
      (json['test'] as List).forEach((v) {
        test!.add(MonthWiseTests.fromJson(v as Map<String, dynamic>));
      });
    }
  }

  List<Subjects>? subjects;
  // 将单个对象改为列表，匹配JSON结构
  List<MonthWiseTests>? test;
  List<String>? filter1;

  // 修复toJson方法（若需要序列化）
  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    if (subjects != null) {
      data['subjects'] = subjects!.map((v) => v.toJson()).toList();
    }
    if (test != null) {
      data['test'] = test!.map((v) => v.toJson()).toList();
    }
    if (filter1 != null) {
      data['filter1'] = filter1;
    }
    return data;
  }
}

2. 修正MonthWiseTests的fromJson方法 #

原来的解析逻辑完全不符合JSON结构，直接读取map['month']和map['tests']字段即可：

class MonthWiseTests {
  MonthWiseTests({
    this.month,
    this.tests,
  });

  factory MonthWiseTests.fromJson(Map<String, dynamic> map) {
    return MonthWiseTests(
      // 直接读取JSON中的month字段
      month: map['month'] as String?,
      // 解析tests数组，并过滤可能的null值
      tests: map['tests'] != null
          ? List<Test>.from(
              (map['tests'] as List<dynamic>).map<Test?>(
                (x) => Test.fromJson(x as Map<String, dynamic>),
              ).whereType<Test>(),
            )
          : null,
    );
  }
  String? month;
  List<Test>? tests;

  MonthWiseTests copyWith({
    String? month,
    List<Test>? tests,
  }) {
    return MonthWiseTests(
      month: month ?? this.month,
      tests: tests ?? this.tests,
    );
  }

  Map<String, dynamic> toJson() {
    return <String, dynamic>{
      'month': month,
      'tests': tests?.map((x) => x.toJson()).toList(),
    };
  }
}

改动说明 #

1. 字段类型对齐：JSON中test是数组，所以TestHistoryEntity的test字段必须定义为List<MonthWiseTests>?，而非单个对象
2. 解析逻辑对齐：遍历json['test']数组，将每个元素（Map类型）传入MonthWiseTests.fromJson生成对象
3. 修复MonthWiseTests解析逻辑：去掉错误的map.keys.first逻辑，直接读取JSON中明确的month和tests字段，同时添加whereType<Test>()过滤可能的null值，避免列表中出现空元素

内容的提问来源于stack exchange，提问作者hobik