解析迭代 JSON 從 Firebase 到 Flutter

Question

如圖所示，我將數據作為迭代 JSON 保存到實時 Firebase 中。

實時 Firebase 數據

[
  {
    "name": "Math",
    "subMenu": [
      {
        "name": "Math1",
        "subMenu": [
          {
            "name": "Math 1.1"
          },
          {
            "name": "Math 1.2",
            "subMenu": [
              {
                "name": "Math 1.2.1",
                "subMenu": [
                  {
                    "name": "Math 1.2.1.1"
                  },
                  {
                    "name": "Math 1.2.1.2"
                  }
                ]
              },
              {
                "name": "Math 1.2.2"
              }
            ]
          }
        ]
      },
      {
        "name": "Math2"
      },
      {
        "name": "Math3",
        "subMenu": [
          {
            "name": "Math 1.3.1"
          },
          {
            "name": "Math 1.3.2"
          }
        ]
      }
    ]
  },
  {
    "name": "Marketing",
    "subMenu": [
      {
        "name": "Promotions",
        "subMenu": [
          {
            "name": "Catalog Price Rule"
          },
          {
            "name": "Cart Price Rules"
          }
        ]
      },
      {
        "name": "Communications",
        "subMenu": [
          {
            "name": "Newsletter Subscribers"
          }
        ]
      }
    ]
  }
]

JSON 在實時中的樣子 Firebase '點擊圖片'

數據模型.dart

class Menu {
  String? name;
  int? font;
  List<Menu>? subMenu = [];

  Menu({this.name, this.subMenu, this.font});

  Menu.fromJson(Map<String, dynamic> json) {
    font = json['font'];
    name = json['name'];

    if (json['subMenu'] != null) {
      json['subMenu'].forEach((v) {
        subMenu?.add(Menu.fromJson(v));
      });
    }
  }
}

我的目標是在 Flutter 中構建一個反映迭代 JSON 結構的多級列表視圖。 因此，我實現了一個返回List<Menu>的方法，然后將其傳遞給Futurebuilder以構建多級列表視圖。

方法。

final ref = FirebaseDatabase.instance.ref();

  Future<List<Menu>> firebaseCalls(DatabaseReference ref) async {
    final snapshot = await ref.child('Task').get();
    final jsondata = snapshot.value as Map<String, dynamic>;
    final list = json.decode(jsondata) as List<dynamic>; // Error Location
    return list.map((e) => Menu.fromJson(e)).toList();
  }

我得到了以下

錯誤error: The argument type 'Map<String, dynamic>' can't be assigned to the parameter type 'String'. (argument_type_not_assignable at [flutter_multilevel_list_from_json] lib\main.dart:28) error: The argument type 'Map<String, dynamic>' can't be assigned to the parameter type 'String'. (argument_type_not_assignable at [flutter_multilevel_list_from_json] lib\main.dart:28)

試圖將列表類型更改為List<dynamic>但仍然給我一個錯誤。

Answer 1

json.decode()將字符串作為輸入，並且您將Map<String,dynamic>傳遞給它。

那是您的問題，而不是您要嘗試將其轉換為List<dynamic>

Answer 2

可能這會有所幫助(jsondata as List).map((e) => Menu.fromJson(e)).toList();