从firebase解析迭代的json
如图所示，我将数据保存到实时燃料中作为迭代JSON。
实时壁炉数据
[
{
"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在实时firebase '单击图像'
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));
});
}
}
}
我的目标是构建反射迭代的JSON结构的多级列表视图。因此，我实施了一种返回list＆lt;菜单＆gt;的方法，然后将其传递到futurebuilder以构建多级列表视图。
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
错误 错误：参数类型'map＆lt; string，dynamic＆gt;'无法分配给参数类型“字符串”。 （grognal_type_not_assignable在[flutter_multilevel_list_from_json] lib \ main.dart：28）
试图将列表类型更改为list＆lt; dynamic＆lt; dynamic＆gt;，但仍然给我错误。
I have data saved into Realtime Firebase as an iterative JSON as shown in the picture.
Realtime Firebase data
[
{
"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"
}
]
}
]
}
]
How the JSON look like in Realtime Firebase
'Click the image'
datamodel.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));
});
}
}
}
My goal is to build a multilevel list view in Flutter that reflexes iterative JSON structure. So, I implemented a method that returns List<Menu>, and then pass it to a Futurebuilder to build a multilevel list View.
The method.
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();
}
and I got the following
The Errorerror: 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)
tried to change the list type to List<dynamic> but still give me an error.
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评论（2）
json.decode（）将字符串作为输入，然后将map＆lt; string，dynamic＆gt;传递到其中。那是您的问题，不是您试图将其施加到
list＆lt; dynamic＆gt;json.decode()takes a String as input, and you are passing aMap<String,dynamic>into it.That is your problem, not that you are trying to cast it to a
List<dynamic>可能这将是有用的
（jsondata作为列表）.map（（e）=＆gt; menu.fromjson（e））。tolist（）;>May be this will be helpful
(jsondata as List).map((e) => Menu.fromJson(e)).toList();