اپ قیمت ارز با فلاتر (Flutter)؛ از JSON تا رابط کاربری راست‌چین

# pubspec.yaml
dependencies:
  flutter:
    sdk: flutter
  flutter_localizations:
    sdk: flutter
  http: ^1.2.0
  intl: ^0.19.0
  shared_preferences: ^2.2.0

class Rate {
  final String symbol, name;
  final num buy, sell, changePct;
  final int sources;
  final DateTime updatedAt;

  Rate.fromJson(Map<String, dynamic> j)
      : symbol = j['symbol'],
        name = j['name'],
        buy = j['buy'],
        sell = j['sell'],
        changePct = j['change_pct'] ?? 0,
        sources = j['sources'] ?? 0,
        updatedAt = DateTime.parse(j['updated_at']);
}

import 'dart:convert';
import 'package:http/http.dart' as http;
import 'package:shared_preferences/shared_preferences.dart';

class RatesService {
  static const _url = 'https://yourapp.com/rates';   // سرور خودتان، نه api.ezrate.me
  static const _cacheKey = 'last_rates';

  Future<List<Rate>> load() async {
    final prefs = await SharedPreferences.getInstance();
    try {
      final res = await http.get(Uri.parse(_url)).timeout(const Duration(seconds: 8));
      if (res.statusCode == 200) {
        await prefs.setString(_cacheKey, res.body);       // آخرین پاسخ معتبر
        return _parse(res.body);
      }
    } catch (_) {/* بدون اینترنت یا خطای سرور */}
    final cached = prefs.getString(_cacheKey);
    return cached == null ? [] : _parse(cached);
  }

  List<Rate> _parse(String body) =>
      (jsonDecode(body)['data'] as List).map((e) => Rate.fromJson(e)).toList();
}

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

final _fa = NumberFormat.decimalPattern('fa');

class RatesPage extends StatefulWidget {
  const RatesPage({super.key});
  @override
  State<RatesPage> createState() => _RatesPageState();
}

class _RatesPageState extends State<RatesPage> {
  final _service = RatesService();
  List<Rate> _rates = [];

  Future<void> _refresh() async {
    final r = await _service.load();
    if (mounted) setState(() => _rates = r);
  }

  @override
  void initState() { super.initState(); _refresh(); }

  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(title: const Text('قیمت لحظه‌ای بازار')),
        body: RefreshIndicator(
          onRefresh: _refresh,
          child: ListView.separated(
            itemCount: _rates.length,
            separatorBuilder: (_, __) => const Divider(height: 1),
            itemBuilder: (_, i) {
              final r = _rates[i];
              final up = r.changePct >= 0;
              return ListTile(
                title: Text(r.name),
                subtitle: Text('${r.sources} منبع'),
                trailing: Column(crossAxisAlignment: CrossAxisAlignment.end, children: [
                  Text('${_fa.format(r.sell)} تومان', style: const TextStyle(fontWeight: FontWeight.bold)),
                  Text('${up ? '▲' : '▼'} ${_fa.format(r.changePct.abs())}٪',
                      style: TextStyle(color: up ? Colors.green : Colors.red)),
                ]),
              );
            },
          ),
        ),
      );
}