Flutter：如何按降序或字母顺序对 ListView（来自 Json 的数据）进行排序？

Question

这是 JSON 文件

[
  {
    "id": 1,
    "country": "United States",
    "population": 328200000
  },
  {
    "id": 2,
    "country": "Germany",
    "population": 83020000
  },
  {
    "id": 3,
    "country": "United Kingdom",
    "population": 66650000
  }
]

我希望在按下RaisedButton 后，它会按顺序排序（'Country Name' => 减少；'Country Population' => 按字母顺序）(image preview)。该怎么做？

这是主文件：

import 'dart:convert';
import 'dart:core';
import 'package:ask/country.dart';
import 'package:ask/country_service.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

void main() => runApp(MyApp());

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

class _MyAppState extends State<MyApp> {
  List<Country> _country = [];

  @override
  void initState() {
    CountryServices.getCountry().then((value) {
      setState(() {
        _country = value;
      });
    });
    super.initState();
  }

  Widget build(BuildContext context) {
    return new MaterialApp(
        home: Scaffold(
            appBar: AppBar(title: Text('Country')),
            body: Container(
                child: Column(children: <Widget>[
                  Row(children: <Widget>[
                      Expanded(
                          flex: 1,
                          child: RaisedButton(
                            child: Text('Country Name'),
                            onPressed: () {}, // Sort alphabetically
                          )),
                      Expanded(
                          flex: 1,
                          child: RaisedButton(
                            child: Text('Country Population'),
                            onPressed: () {}, // Sort in decreasing order
                          ))]),
                   Container(
                      child: ListView.builder(
                        shrinkWrap: true,
                        itemCount: _country.length,
                        itemBuilder: (context, index) {
                          return _listCountry(index);
                        }))
            ]))));
  }

  _listCountry(index) {
    Country country = _country[index];
    return Row(
      children: <Widget>[
        Expanded(
            flex: 1,
            child: Text(
              country.country,
              textAlign: TextAlign.center,
            )),
        Expanded(
            flex: 1,
            child: Text('${country.population}', textAlign: TextAlign.center)),
      ],
    );
  }
}

Answer 1

This官方文档会提供如何排序的信息。

试试下面的。

CountryServices.getCountry().then((value) {


    setState(() {
        _country = value;
        _country.sort((a, b) => a.population.compareTo(b.population));
    });
});

注意：以上代码未经测试。您可能需要稍作调整。