我如何使用Flutter中从json解析的嵌套地图列表中的函数创建对象 [英] How do i create an object using a function from a list of nested maps parse from json in Flutter

问题描述

我正在寻求有关先前问题的帮助

I'm looking for help expanding on an earlier question Question which showed me one way to access the json data in MovementDataSource. In that case on the first page the user is presented a list of movements using a listview and getMovements(). After selecting a movement the user on page 2 is presented a list of variations via a listview and getVariationsByMovement(). Then after selecting the variation the user is presented page 3 that gives me access to all of the items in the singular VariationModel. (right now it's only variationName)

我还有另一个用例，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-我可以传递这两个变量并给我一个VariationName对象的函数示例，以直接将链接的构造函数传递给第3页.在下面的MovementDataSource中有一个getVariation()我希望得到帮助的功能.

I have another use case where I am in another part of the application but need to jump directly to page 3 bypassing the user workflow of Page 1 and Page 2 above. At that moment I have access to the String Movement and the String VariationName. I'm looking for help - an example of a function that I could pass in those two variables and give me back a VariationName object to pass in the constructor of the link directly to page 3. In MovementDataSource below there is a getVariation() function I am hoping to have help with.

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页的一个示例-在本用例中为直接目标.

An example of the Page 3 above - the direct target in this use case.

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));
  }
}

示例源页面，其中包括直接链接到上述第3页目标的页面.这是调用getVariation()函数的地方，将VariationModel传递到上面的SourcePage.

example of the source page that includes a direct link to page 3 target above. This is where the getVariation() function would be called passing a VariationModel to SourcePage above.

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.

推荐答案

您可以在
下复制粘贴运行完整代码 您可以将movementDataSource，movement和variation传递给SourcePage
然后在SourcePage通话中

You can copy paste run full code below
You can pass movementDataSource, movement and variation to SourcePage
And in SourcePage call

TargetPage(variation: movementDataSource.getVariation(
                            movement: movement,
                            variation: variation.variationName))

代码段

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));
  }
}

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