Question

您好，我正在使用以下功能按键分组并计算总计：

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter_localizations/flutter_localizations.dart';

class MyCount {
  String count;

  MyCount({this.count});
}

class MyCountLocale extends LocalizationsDelegate<MyCount> {
  MyCount data;

  MyCountLocale(this.data);

  @override
  bool isSupported(Locale locale) {
    return true;
  }

  @override
  Future<MyCount> load(Locale locale) async {
    return data;
  }

  @override
  bool shouldReload(MyCountLocale old) {
    return old.data != data;
  }
}

Future<void> main() async {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  ValueNotifier<int> count = ValueNotifier<int>(0);
  LocalizationsDelegate myLocale;

  @override
  void initState() {
    count.addListener(() {
      setState(() {
        myLocale = MyCountLocale(MyCount(count: count.value.toString()));
      });
    });
    myLocale = MyCountLocale(MyCount(count: count.value.toString()));

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      localizationsDelegates: [
        myLocale,
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
      ],
      home: MyHomePage(count: count),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final ValueNotifier<int> count;

  MyHomePage({this.count});

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      primary: true,
      appBar: AppBar(),
      body: Column(
        children: <Widget>[
          FloatingActionButton(
            onPressed: () => widget.count.value++,
            child: Icon(Icons.plus_one),
          ),
          ListTile(
            title: Text(Localizations.of<MyCount>(context, MyCount).count),
          ),
        ],
      ),
    );
  }
}

除了第一个项目是一个空对象之外，这工作得很好，我在这里做错什么了？

calcEquipmentTotals(){
    var groups = this.inspection.equipments.reduce(function(obj,item){
      obj[item.equipment_type_id] = obj[item.equipment_type_id] || { equipment_type_id: item.equipment_type_id, total: 0};
      // Calculate total based on action
      var total = obj[item.equipment_type_id].total;
      if(item.action === 'added' || item.action === 'stocktake'){
        total = total + item.quantity;
      }else{
        total = total - item.quantity;
      };
      obj[item.equipment_type_id].total = total;
      return obj;
    },[]);
    return groups;
  }

Answer 1

这会做你想要的。

 calcEquipmentTotals() {
  var groups = this.inspection.equipments.reduce(function (map, item) {

    const obj = map.get(item.equipment_type_id) || {
      equipment_type_id: item.equipment_type_id, total: 0
    };

    if (item.action === 'added' || item.action === 'stocktake') {
      obj.total += item.quantity;
    } else {
      obj.total -= item.quantity;
    };
    map.set(obj);

    return map;
  }, new Map());
  return Array.from(groups.values());
}

Answer 2

这些评论为我指明了正确的方向，这是最终完成的事情：

calcEquipmentTotals(){
    var groups = this.inspection.equipments.reduce(function(obj,item){
      obj[item.equipment_type_id] = obj[item.equipment_type_id] || { equipment_type_id: item.equipment_type_id, total: 0};
      // Calculate total based on action
      var total = obj[item.equipment_type_id].total;
      if(item.action === 'added' || item.action === 'stocktake'){
        total = total + item.quantity;
      }else{
        total = total - item.quantity;
      };
      obj[item.equipment_type_id].total = total;
      return obj;
    },{});
    return Object.keys(groups).map((key) => groups[key]);
  }

JS Reduce返回数组中的第一项为null

2 个答案: