如何使用从 Flutter 中的 json 解析的嵌套映射列表中的函数创建对象
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【中文标题】如何使用从 Flutter 中的 json 解析的嵌套映射列表中的函数创建对象【英文标题】：How do i create an object using a function from a list of nested maps parse from json in Flutter 【发布时间】：2021-01-14 14:56:19 【问题描述】：我正在寻求帮助扩展之前的问题Question，该问题向我展示了一种访问MovementDataSource 中的 json 数据的方法。在这种情况下，在第一页上，使用列表视图和getMovements() 向用户呈现移动列表。选择一个动作后，第 2 页上的用户会通过列表视图和getVariationsByMovement() 看到一个变化列表。然后在选择变体后，用户会看到第 3 页，它让我可以访问单数 VariationModel 中的所有项目。 （现在只是变体名称）
我有另一个用例，我在应用程序的另一部分，但需要绕过上面第 1 页和第 2 页的用户工作流程直接跳转到第 3 页。那时我可以访问String Movement 和String VariationName。我正在寻求帮助 - 我可以传入这两个变量并返回一个 VariationName 对象以将链接的构造函数直接传递到第 3 页的函数示例。在下面的 MovementDataSource 中有一个getVariation() 函数我希望能得到帮助。
class MovementDataSource extends ChangeNotifier
List<Map> getAll() => _movement;
List<String> getMovements()=> _movement
.map((map) => MovementModel.fromJson(map))
.map((item) => item.movement)
.toList();
getVariationsByMovement(String movement) => _movement
.map((map) => MovementModel.fromJson(map))
.where((item) => item.movement == movement)
.map((item) => item.variation)
.expand((i) => i)
.toList();
VariationModel getVariation(String movement, String variation)
**Return VariationModel from List _movement json**
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,
;
上面第 3 页的示例 - 本用例中的直接目标。
class TargetPage extends StatelessWidget
final VariationModel variation;
SelectDefaultItemPage(this.variation);
@override
Widget build(BuildContext context)
return Scaffold(
appBar: AppBar(
title: Text("test"),
),
body: Text(variation.variationName));
包含指向上述第 3 页目标的直接链接的源页面示例。这是调用 getVariation() 函数的地方，将 VariationModel 传递给上面的 SourcePage。
class SourcePage extends StatelessWidget
final VariationModel variation;
SelectDefaultItemPage(this.variation);
@override
Widget build(BuildContext context)
return Scaffold(
appBar: AppBar(
title: Text("test"),
),
body:FlatButton(
child: Text(
"Go to TargetPage",
),
onPressed: () async Navigator.push(context, MaterialPageRoute(
builder: (_) => SourcePage(getVariation(movement: movement, variation:
variation)));
,
)
感谢您的帮助。
【问题讨论】：
【参考方案1】：您可以在下面复制粘贴运行完整代码
您可以将movementDataSource、movement 和variation 传递给SourcePage
并在SourcePage 通话中
TargetPage(variation: movementDataSource.getVariation(
movement: movement,
variation: variation.variationName))
代码sn-p
VariationModel getVariation(String movement, String variation) => _movement
.map((map) => MovementModel.fromJson(map))
.where((item) => item.movement == movement)
.map((item) => item.variation)
.expand((i) => i)
.where((e) => e.variationName == variation)
.first;
...
onTap: () async
Navigator.push(
context,
MaterialPageRoute(
builder: (_) => SourcePage(
movementDataSource: _movementDataSource,
movement: movement,
variation: vList[index])));
,
...
class SourcePage extends StatelessWidget
final MovementDataSource movementDataSource;
final String movement;
final VariationModel variation;
SourcePage(this.movementDataSource, this.movement, this.variation);
@override
Widget build(BuildContext context)
return Scaffold(
...
onPressed: () async
Navigator.push(
context,
MaterialPageRoute(
builder: (_) => TargetPage(
variation: movementDataSource.getVariation(
movement: movement,
variation: variation.variationName))));
,
));
...
class TargetPage extends StatelessWidget
final VariationModel variation;
TargetPage(this.variation);
工作演示
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();
VariationModel getVariation(String movement, String variation) => _movement
.map((map) => MovementModel.fromJson(map))
.where((item) => item.movement == movement)
.map((item) => item.variation)
.expand((i) => i)
.where((e) => e.variationName == variation)
.first;
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;
String movement = "Plank";
MovementDataSource _movementDataSource = MovementDataSource();
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(movement);
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: (_) => SourcePage(
movementDataSource: _movementDataSource,
movement: movement,
variation: vList[index])));
,
),
);
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
class SourcePage extends StatelessWidget
final MovementDataSource movementDataSource;
final String movement;
final VariationModel variation;
SourcePage(this.movementDataSource, this.movement, this.variation);
@override
Widget build(BuildContext context)
return Scaffold(
appBar: AppBar(
title: Text("Source page"),
),
body: FlatButton(
child: Text(
"Go to TargetPage",
),
onPressed: () async
Navigator.push(
context,
MaterialPageRoute(
builder: (_) => TargetPage(
variation: movementDataSource.getVariation(
movement: movement,
variation: variation.variationName))));
,
));
class TargetPage extends StatelessWidget
final VariationModel variation;
TargetPage(this.variation);
@override
Widget build(BuildContext context)
return Scaffold(
appBar: AppBar(
title: Text("Target page"),
),
body: Text(variation.variationName));
【讨论】：
这正是我想要的。我希望在您提供的答案之间，我可以开始对如何更好地使用列表、地图和数据进行三角测量。您是否知道使用function() => data.doSomething.doSomething 结构关注这一领域的任何文档或教程？
＠nejas，可以参考codeburst.io/…和bezkoder.com/dart-list以上是关于如何使用从 Flutter 中的 json 解析的嵌套映射列表中的函数创建对象的主要内容，如果未能解决你的问题，请参考以下文章
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