json - 如何在 Flutter 中返回带有映射列表的嵌套结构的值
问题描述
仍在尝试学习地图和列表。
我的目标是从嵌套的地图列表中返回一个列表。函数 getMovements() 按预期工作。它呈现一个动作列表。然后,我尝试创建另一个函数 getVariationsByMovement(),它传入移动字符串名称以尝试返回变体名称列表。在我的 UI 中,我展示了一个动作列表。用户选择一个动作,下一页呈现一个变化列表。
我被困在 getVariationsByMovement 下面的函数中。
class MovementDataSource extends ChangeNotifier{
List<Map> getAll() => _movement;
List<String> getMovements()=> _movement
.map((map) => MovementModel.fromJson(map))
.map((item) => item.movement)
.toList();
// I'd like this to return a list of movement.variation.variationName
getVariationsByMovement(String movement) => _movement
.map((map) => MovementModel.fromJson(map))
.where((item) => item.movement == movement)
.map((item) => item.**I AM STUCK HERE**)
.expand((i) => i)
.toList();
List _movement = [
{
"movement": "Plank",
"alias": "plank",
"variation": [
{"variationName": "High Plank"}, {"variationName": "Forearm Plank"},
]
},
{
"movement": "Side Plank",
"alias": "side plank",
"variation": [
{"variationName": "Side Plank Right"}, {"variationName": "Side Plank Left"},
],
},
];
}
我的模型
class MovementModel {
String movement;
String alias;
List<VariationModel> variation;
MovementModel({this.movement, this.alias, this.variation});
// from firestore
MovementModel.fromJson(Map<String, dynamic> json) {
var list = json['variation'] as List;
List<VariationModel> variationList = list.map((i) => VariationModel.fromJson(i)).toList();
movement = json['movement'];
alias = json['alias'];
variation = variationList;
}
// to firestore
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = new Map<String, dynamic>();
data['movement'] = this.movement;
data['alias'] = this.alias;
//data['variation'] = VariationModel;
return data;
}
}
class VariationModel {
String variationName;
String description;
VariationModel({this.variationName, this.description});
// from firestore
VariationModel.fromJson(Map<String, dynamic> json) {
variationName = json['variationName'];
description = json['description'];
}
// to firestore
Map<String, dynamic> toJson() {
return {
'variationName': variationName,
'description': description,
};
}
}
更新在这种情况下,我试图将结果返回给列表生成器。
@override
Widget build(BuildContext context) {
final _movementDataLocator = locator<MovementDataSource>();
return ListView.builder(
scrollDirection: Axis.vertical,
shrinkWrap: true,
itemCount: _movementDataLocator.getVariationsByMovement(movement).length,
itemBuilder: (buildContext, index) {
return Card(
child: ListTile (
title: Text(
_movementDataLocator.getVariationsByMovement(movement)[index].toString(),
style: TextStyle(fontSize: 20),
),
trailing: Icon(Icons.keyboard_arrow_right),
onTap: () async {
Navigator.push(context, MaterialPageRoute(
builder: (_) => SelectDefaultItemPage(variation: _movementDataLocator.getVariationsByMovement(movement)[index])));
},
),
);
}
);
}
}
解决方案
您可以在下面复制粘贴运行完整代码
您可以使用variation: List<VariationModel>.from(json["variation"].map((x) => VariationModel.fromJson(x))
代码片段
factory MovementModel.fromJson(Map<String, dynamic> json) => MovementModel(
movement: json["movement"],
alias: json["alias"],
variation: List<VariationModel>.from(
json["variation"].map((x) => VariationModel.fromJson(x))),
);
...
List<VariationModel> vList =
MovementDataSource().getVariationsByMovement("Plank");
for (int i = 0; i < vList.length; i++) {
print(vList[i].variationName);
}
输出
I/flutter (21879): High Plank
I/flutter (21879): Forearm Plank
完整代码
import 'package:flutter/material.dart';
import 'dart:convert';
List<MovementModel> movementModelFromJson(String str) =>
List<MovementModel>.from(
json.decode(str).map((x) => MovementModel.fromJson(x)));
String movementModelToJson(List<MovementModel> data) =>
json.encode(List<dynamic>.from(data.map((x) => x.toJson())));
class MovementDataSource extends ChangeNotifier {
List<Map> getAll() => _movement;
List<String> getMovements() => _movement
.map((map) => MovementModel.fromJson(map))
.map((item) => item.movement)
.toList();
// I'd like this to return a list of movement.variation.variationName
getVariationsByMovement(String movement) => _movement
.map((map) => MovementModel.fromJson(map))
.where((item) => item.movement == movement)
.map((item) => item.variation)
.expand((i) => i)
.toList();
List _movement = [
{
"movement": "Plank",
"alias": "plank",
"variation": [
{"variationName": "High Plank"},
{"variationName": "Forearm Plank"},
]
},
{
"movement": "Side Plank",
"alias": "side plank",
"variation": [
{"variationName": "Side Plank Right"},
{"variationName": "Side Plank Left"},
],
},
];
}
class MovementModel {
MovementModel({
this.movement,
this.alias,
this.variation,
});
String movement;
String alias;
List<VariationModel> variation;
factory MovementModel.fromJson(Map<String, dynamic> json) => MovementModel(
movement: json["movement"],
alias: json["alias"],
variation: List<VariationModel>.from(
json["variation"].map((x) => VariationModel.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"movement": movement,
"alias": alias,
"variation": List<dynamic>.from(variation.map((x) => x.toJson())),
};
}
class VariationModel {
VariationModel({
this.variationName,
});
String variationName;
factory VariationModel.fromJson(Map<String, dynamic> json) => VariationModel(
variationName: json["variationName"],
);
Map<String, dynamic> toJson() => {
"variationName": variationName,
};
}
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
List<VariationModel> vList =
MovementDataSource().getVariationsByMovement("Plank");
for (int i = 0; i < vList.length; i++) {
print(vList[i].variationName);
}
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
工作演示
完整代码 2
import 'package:flutter/material.dart';
import 'dart:convert';
List<MovementModel> movementModelFromJson(String str) =>
List<MovementModel>.from(
json.decode(str).map((x) => MovementModel.fromJson(x)));
String movementModelToJson(List<MovementModel> data) =>
json.encode(List<dynamic>.from(data.map((x) => x.toJson())));
class MovementDataSource extends ChangeNotifier {
List<Map> getAll() => _movement;
List<String> getMovements() => _movement
.map((map) => MovementModel.fromJson(map))
.map((item) => item.movement)
.toList();
// I'd like this to return a list of movement.variation.variationName
getVariationsByMovement(String movement) => _movement
.map((map) => MovementModel.fromJson(map))
.where((item) => item.movement == movement)
.map((item) => item.variation)
.expand((i) => i)
.toList();
List _movement = [
{
"movement": "Plank",
"alias": "plank",
"variation": [
{"variationName": "High Plank"},
{"variationName": "Forearm Plank"},
]
},
{
"movement": "Side Plank",
"alias": "side plank",
"variation": [
{"variationName": "Side Plank Right"},
{"variationName": "Side Plank Left"},
],
},
];
}
class MovementModel {
MovementModel({
this.movement,
this.alias,
this.variation,
});
String movement;
String alias;
List<VariationModel> variation;
factory MovementModel.fromJson(Map<String, dynamic> json) => MovementModel(
movement: json["movement"],
alias: json["alias"],
variation: List<VariationModel>.from(
json["variation"].map((x) => VariationModel.fromJson(x))),
);
Map<String, dynamic> toJson() => {
"movement": movement,
"alias": alias,
"variation": List<dynamic>.from(variation.map((x) => x.toJson())),
};
}
class VariationModel {
VariationModel({
this.variationName,
});
String variationName;
factory VariationModel.fromJson(Map<String, dynamic> json) => VariationModel(
variationName: json["variationName"],
);
Map<String, dynamic> toJson() => {
"variationName": variationName,
};
}
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
List<VariationModel> vList =
MovementDataSource().getVariationsByMovement("Plank");
for (int i = 0; i < vList.length; i++) {
print(vList[i].variationName);
}
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
List<VariationModel> vList =
MovementDataSource().getVariationsByMovement("Plank");
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: ListView.builder(
scrollDirection: Axis.vertical,
shrinkWrap: true,
itemCount: vList.length,
itemBuilder: (buildContext, index) {
return Card(
child: ListTile(
title: Text(
vList[index].variationName.toString(),
style: TextStyle(fontSize: 20),
),
trailing: Icon(Icons.keyboard_arrow_right),
onTap: () async {
Navigator.push(
context,
MaterialPageRoute(
builder: (_) =>
SelectDefaultItemPage(variation: vList[index])));
},
),
);
}),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
class SelectDefaultItemPage extends StatelessWidget {
final VariationModel variation;
SelectDefaultItemPage({this.variation});
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("test"),
),
body: Text(variation.variationName));
}
}
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