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[英]Why I can't get $this->post() value from JSON.stringify POST data
[英]Why can't i get data value from json - flutter
Am trying to get values from my json file categories.json
using flutter but am always getting error or its not showing and I don't really know what is wrong This is my main.dart
Future<List<Category>> loadData() async {
String jString = await rootBundle.loadString("assets/categories.json");
List<dynamic> jRes = jsonDecode(jString);
List<Category> datas = jRes.map((e) => Category.fromJson(e)).toList();
return datas;
}
Container(
child: FutureBuilder<List<Category>>(
future: loadData(),
builder: (context, data) {
if (data.connectionState != ConnectionState.waiting &&
data.hasData) {
var userList = data.data;
return ListView.builder(
itemCount: userList.length,
itemBuilder: (context, index) {
var userData = userList[index];
return Column(
children: [
Text("Category: ${userData.catName}"),
],
);
});
} else {
return Center(
child: CircularProgressIndicator(),
);
}
})),
和我的model.dart
class Category {
String catId;
String catName;
SubCategory subcat;
Category({this.catId, this.catName, this.subcat});
factory Category.fromJson(Map<String, dynamic> json) {
return Category(
catId: json['cat_id'],
catName: json['category'],
subcat: SubCategory.fromJson(json['cat_subcategory']),
);
}
Map<String, dynamic> toJson() {
return {
"cat_id": catId,
"category": catName,
};
}
}
class SubCategory {
String subName, subImage;
SubCategory({this.subName, this.subImage});
factory SubCategory.fromJson(Map<String, dynamic> json) {
return SubCategory(subName: json['sub_name'], subImage: json['sub_image']);
}
Map<String, dynamic> toJson() {
return {
"sub_name": subName,
"sub_image": subImage,
};
}
}
最后是我的categories.json文件
[{
"category": "Design & Creativity",
"cat_id": "1",
"cat_subcategory": [
{
"sub_name": "Ads",
"sub_image": "https://images.unsplash.com/photo-1589838017489-9198a27bd040?ixid=MXwxMjA3fDB8MHxzZWFyY2h8Mnx8YWR2ZXJ0aXNlbWVudHxlbnwwfHwwfA%3D%3D&ixlib=rb-1.2.1&auto=format&fit=crop&w=500&q=60"
}
]
}]
//There are more of them
當我運行它時面臨的問題是它只在我的main.dart中向我顯示CircularProgressIndicator()
,當我刪除if 語句時,它說Another exception was thrown: NoSuchMethodError: The getter 'length' was called on null.
請問我如何解決這個問題,如果您需要更多解釋,請告訴我
PS:當我檢查loadData()
值時,它說type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>'
編輯:謝謝大家的回答,但我所做的是使用此網站model 生成器生成 model
我能夠獲得價值
就個人而言,當我想從 json 文件加載數據時,我這樣做:
Future<List<Category>> loadData() async {
List<Category> datas = [];
return rootBundle.loadString("assets/categories.json").then((value) {
List<dynamic> jRes = jsonDecode(value);
jRes.forEach((element) {
datas.add(Category.fromJson(element));
});
return datas;
});
}
此外,在子類別class
factory SubCategory.fromJson(Map<String, dynamic> json) {
return SubCategory(subName: json['sub_name'], subImage: json['sub_image']);
}
您的fromJson()需要Map<String, dynamic> 。
但是如果你看你的文件
"cat_subcategory": [
{
"sub_name": "Ads",
"sub_image": "https://images.unsplash.com/photo-1589838017489-9198a27bd040?ixid=MXwxMjA3fDB8MHxzZWFyY2h8Mnx8YWR2ZXJ0aXNlbWVudHxlbnwwfHwwfA%3D%3D&ixlib=rb-1.2.1&auto=format&fit=crop&w=500&q=60"
}
]
可以看到cat_subcategory是一個 List
所以你給你的 SubCategory.fromJson ()一個列表,而不是一個 Map。 如果你想給出一個 Map,你可以簡單地給出你列表的第一個索引
您的 Category.fromJson() 成為
factory Category.fromJson(Map<String, dynamic> json) {
return Category(
catId: json['cat_id'],
catName: json['category'],
subcat: SubCategory.fromJson(json['cat_subcategory'][0]),
);
}
更改您的 model.dart class
class Category {
String category;
String catId;
List<CatSubcategory> catSubcategory;
Category({this.category, this.catId, this.catSubcategory});
Category.fromJson(Map<String, dynamic> json) {
category = json['category'];
catId = json['cat_id'];
if (json['cat_subcategory'] != null) {
catSubcategory = new List<CatSubcategory>();
json['cat_subcategory'].forEach((v) {
catSubcategory.add(new CatSubcategory.fromJson(v));
});
}}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = new Map<String, dynamic>();
data['category'] = this.category;
data['cat_id'] = this.catId;
if (this.catSubcategory != null) {
data['cat_subcategory'] =
this.catSubcategory.map((v) => v.toJson()).toList();
}
return data;
}}
class CatSubcategory {
String subName;
String subImage;
CatSubcategory({this.subName, this.subImage});
CatSubcategory.fromJson(Map<String, dynamic> json) {
subName = json['sub_name'];
subImage = json['sub_image'];
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = new Map<String, dynamic>();
data['sub_name'] = this.subName;
data['sub_image'] = this.subImage;
return data;
}}
並替換
List<Category> datas = jRes.map((e) => Category.fromJson(e)).toList();
和
List<Category> datas = List<Category>.from(jRes.map((category)=> Category.fromJson(category)));
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