dart 中的高级 json 解析

Question

我想解析这个 Json。现在我将Load 解析为具有2 个字段的类：id 和value。但我想要的是像Map<int, String> 一样解析它。当我尝试投射对象时，颤动给了我一个错误。例如：

Map<int, String> map = {
  38 : "#1038 Fort Dodge, IA - Algona, IA",
  39 : "#1039 Louisville, KY - Louisville, KY"
}

和this question不一样

{
    "loads": {
      "data": [
        {
          "id": 38,
          "value": "#1038 Fort Dodge, IA - Algona, IA"
        },
        {
          "id": 39,
          "value": "#1039 Louisville, KY - Louisville, KY"
        }
      ]
    },
    "date_ranges": {
      "data": [
        {
          "id": "all_time",
          "value": "All"
        },
        {
          "id": "this_year",
          "value": "This year"
        }
      ]
    }
  }

Answer 1

您发现了一个问题，因为 loads 和 date_ranges 包含相同的子名称 data 但属性不同，这就是您的模型类返回错误的原因

这里我写了一个加载代码，请大家看看

void main() {

 Map<int, String> map = {
};
  
  var mapdata = {
    "loads": {
      "data": [
        {
          "id": 50,
          "value": "#1038 Fort Dodge, IA - Algona, IA"
        },
        {
          "id": 39,
          "value": "#1039 Louisville, KY - Louisville, KY"
        }
      ]
    },
    "date_ranges": {
      "data": [
        {
          "id": "all_time",
          "value": "All"
        },
        {
          "id": "this_year",
          "value": "This year"
        }
      ]
    }
  };
  TestModel test = TestModel.fromJson(mapdata);
  test.loads.data.forEach((e)=>map[e.id]=e.value);
  
  print(map);
}

class TestModel {
  Loads loads;
  Loads dateRanges;

  TestModel({this.loads, this.dateRanges});

  TestModel.fromJson(Map<String, dynamic> json) {
    loads = json['loads'] != null ? new Loads.fromJson(json['loads']) : null;
    dateRanges = json['date_ranges'] != null
        ? new Loads.fromJson(json['date_ranges'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.loads != null) {
      data['loads'] = this.loads.toJson();
    }
    if (this.dateRanges != null) {
      data['date_ranges'] = this.dateRanges.toJson();
    }
    return data;
  }
}

class Loads {
  List<Data> data;

  Loads({this.data});

  Loads.fromJson(Map<String, dynamic> json) {
    if (json['data'] != null) {
      data = new List<Data>();
      json['data'].forEach((v) {
        data.add(new Data.fromJson(v));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.data != null) {
      data['data'] = this.data.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class Data {
  var id; // here changes the type
  String value;

  Data({this.id, this.value});

  Data.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    value = json['value'];
  }

  Map<String, String> toJson() {
    final Map<String, String> data = new Map<String, String>();
    data['id'] = this.id;
    data['value'] = this.value;
    return data;
  }
}

地图结果：

{50: #1038 Fort Dodge, IA - Algona, IA, 39: #1039 Louisville, KY - Louisville, KY}

注意：使用 var 类型使您的 id 动态化

Answer 2

你可以创建 pojo 类来解析你的 JSON

TestModel testModel = TestModel.fromJson(yourResponse);


 class TestModel {
  Loads loads;
  Loads dateRanges;

  TestModel({this.loads, this.dateRanges});

  TestModel.fromJson(Map<String, dynamic> json) {
    loads = json['loads'] != null ? new Loads.fromJson(json['loads']) : null;
    dateRanges = json['date_ranges'] != null
        ? new Loads.fromJson(json['date_ranges'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.loads != null) {
      data['loads'] = this.loads.toJson();
    }
    if (this.dateRanges != null) {
      data['date_ranges'] = this.dateRanges.toJson();
    }
    return data;
  }
}

class Loads {
  List<Data> data;

  Loads({this.data});

  Loads.fromJson(Map<String, dynamic> json) {
    if (json['data'] != null) {
      data = new List<Data>();
      json['data'].forEach((v) {
        data.add(new Data.fromJson(v));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.data != null) {
      data['data'] = this.data.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class Data {
  int id;
  String value;

  Data({this.id, this.value});

  Data.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    value = json['value'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['id'] = this.id;
    data['value'] = this.value;
    return data;
  }
}

class Data {
  String id;
  String value;

  Data({this.id, this.value});

  Data.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    value = json['value'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['id'] = this.id;
    data['value'] = this.value;
    return data;
  }
}