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samples/null_safety/null_unsafe_app/lib/main.dart

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// Copyright 2020, the Flutter project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
import 'dart:io';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:window_size/window_size.dart';
void main() {
setupWindow();
runApp(const MyApp());
}
const double windowWidth = 400;
const double windowHeight = 400;
void setupWindow() {
if (!kIsWeb && (Platform.isWindows || Platform.isLinux || Platform.isMacOS)) {
WidgetsFlutterBinding.ensureInitialized();
setWindowTitle('Weather');
setWindowMinSize(const Size(windowWidth, windowHeight));
}
}
// This app simulates possible null errors. Try running it and see if it fails.
// You can then try to hot reload a few times; you should see it occasionally
// failing and occasionally succeeding.
class MyApp extends StatelessWidget {
const MyApp({Key key}) : super(key: key);
@override
Widget build(BuildContext context) {
// Get data from services. Note: in a real application,
// these would be async calls, but were using sync calls
// for simplicity.
final localizedAppName = Config.getAppName();
final temperatures = WeatherService.getTemperatures();
return MaterialApp(
home: Scaffold(
appBar: AppBar(title: Text(localizedAppName)),
body: Padding(
padding: const EdgeInsets.all(8.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
const Text('Temperature next 3 days:'),
for (final t in temperatures) Text(t.round().toString()),
],
),
),
),
);
}
}
class Config {
static String getAppName() {
// Imagine this looks up a localized version of the app name. We're using
// the current time to simulate a variance in responses.
if (DateTime.now().second.isEven) {
return 'Weather forecast';
} else {
// Oops, we don't have a localization.
return null;
}
}
}
class WeatherService {
static List<double> getTemperatures() {
// Imagine this makes a network call to get the current temperature.
// We're using the current time to simulate a variance in responses.
if (DateTime.now().millisecond.isEven) {
return [32.2, 34.5, 31.0];
} else {
if ((DateTime.now().second / 10).round().isEven) {
// Oops, we couldn't get any temperatures.
return null;
} else {
// Oops, we couldn't get one of the temperatures.
return [32.2, 34.5, null, 31.0];
}
}
}
}