Weather App: Try Again

Part of the Data and the Network section of Coddy's Flutter journey. Lesson 26 of 27.

Weather apps get opened on trains, in tunnels and on mountains. Without a signal, the app should say so plainly and offer a way back, not a spinner that never ends or a line of error text.

Give the error its own small screen: an icon, a sentence a person understands, the details under it, and a Try again button that makes a new future in setState. Put it in its own method, buildError, next to buildWeather, so build stays short.

if (snapshot.connectionState == ConnectionState.waiting) {
  return const CircularProgressIndicator();
}
if (snapshot.hasError) {
  return buildError(snapshot.error!);
}
return buildWeather(snapshot.data!);

Checking ConnectionState.waiting first shows the spinner during every load, the second try included. Once the future is done there is either an error or data, so the last line can use snapshot.data!.

To see it in the preview, write offline = true; as the first line of main and press Run. Take it out before you press Check.

Challenge

Medium

Give the app an error screen:

a buildError(Object error) method: Icons.cloud_off (size 64), Could not load the weather (size 20), the error's text, and a Try again button
a tryAgain method that sets a new loadWeather() in setState
in the builder, check ConnectionState.waiting first, then the error, then show the weather

Try it yourself

import 'dart:convert';

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

import 'api.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      home: WeatherScreen(),
    );
  }
}

class WeatherScreen extends StatefulWidget {
  const WeatherScreen({super.key});

  @override
  State<WeatherScreen> createState() => _WeatherScreenState();
}

class _WeatherScreenState extends State<WeatherScreen> {
  late Future<Weather> _weather;

  @override
  void initState() {
    super.initState();
    _weather = loadWeather();
  }

  Future<Weather> loadWeather() async {
    final body = await fetch('/weather/lisbon');
    return Weather.fromJson(jsonDecode(body));
  }

  IconData iconFor(String condition) {
    return switch (condition) {
      'Sunny' => Icons.wb_sunny,
      'Cloudy' => Icons.cloud,
      'Rainy' => Icons.umbrella,
      'Snowy' => Icons.ac_unit,
      _ => Icons.help_outline,
    };
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Weather')),
      body: Center(
        child: FutureBuilder<Weather>(
          future: _weather,
          builder: (context, snapshot) {
            if (snapshot.hasError) {
              return Text('Could not load: ${snapshot.error}');
            }
            if (snapshot.hasData) {
              return buildWeather(snapshot.data!);
            }
            return const CircularProgressIndicator();
          },
        ),
      ),
    );
  }

  Widget buildWeather(Weather weather) {
    return Column(
      mainAxisSize: MainAxisSize.min,
      children: [
        Text(weather.city, style: const TextStyle(fontSize: 32)),
        Icon(iconFor(weather.condition), size: 96, color: Colors.orange),
        Text(
          '${weather.temperature}°',
          style: const TextStyle(fontSize: 72, fontWeight: FontWeight.bold),
        ),
        Text(weather.condition, style: const TextStyle(fontSize: 24)),
        const SizedBox(height: 32),
        for (final day in weather.forecast)
          Padding(
            padding: const EdgeInsets.symmetric(horizontal: 32, vertical: 8),
            child: Row(
              children: [
                Icon(iconFor(day.condition)),
                const SizedBox(width: 16),
                Expanded(
                  child: Text(
                    DateFormat('EEEE').format(day.date),
                    style: const TextStyle(fontSize: 18),
                  ),
                ),
                Text('${day.high}° / ${day.low}°', style: const TextStyle(fontSize: 18)),
              ],
            ),
          ),
      ],
    );
  }
}

class Weather {
  Weather({
    required this.city,
    required this.temperature,
    required this.condition,
    required this.forecast,
  });

  final String city;
  final int temperature;
  final String condition;
  final List<DayForecast> forecast;

  factory Weather.fromJson(Map<String, dynamic> json) {
    final days = json['forecast'] as List<dynamic>;
    return Weather(
      city: json['city'] as String,
      temperature: json['temperature'] as int,
      condition: json['condition'] as String,
      forecast: days
          .map((day) => DayForecast.fromJson(day as Map<String, dynamic>))
          .toList(),
    );
  }
}

class DayForecast {
  DayForecast({
    required this.date,
    required this.condition,
    required this.high,
    required this.low,
  });

  final DateTime date;
  final String condition;
  final int high;
  final int low;

  factory DayForecast.fromJson(Map<String, dynamic> json) {
    return DayForecast(
      date: DateTime.parse(json['date'] as String),
      condition: json['condition'] as String,
      high: json['high'] as int,
      low: json['low'] as int,
    );
  }
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Data and the Network

Practice on your own: Online Flutter compiler