How to Build Mobile Apps with Flutter?

Step 6: Adding Functionality and Logic

Dart is the programming language used in Flutter development, allowing you to implement the logic of your app. Here are some common tasks you may need to implement:

One of the most common functionalities is handling user input, whether it's through buttons, text input fields, or gestures. Here's an example of a button press handler:

ElevatedButton(
  onPressed: () {
    // Logic to execute when the button is pressed
    print('Button Pressed!');
  },
  child: Text('Press Me'),
)

If your app needs to retrieve data from a server, you can use the 'http' package in Dart or equivalent packages. Here's an example of fetching data from an API:

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

void fetchData() async {
  final response = await http.get(Uri.parse('https://api.example.com/data'));
  if (response.statusCode == 200) {
    print('Data fetched: ${response.body}');
  } else {
    print('Failed to fetch data');
  }
}

Business logic refers to the rules and operations governing your app's functions, which can involve calculations, data processing, or other tasks specific to your app's purpose. Here's an example of a simple calculation:

int calculateTotal(List numbers) {
  int total = 0;
  for (int number in numbers) {
    total += number;
  }
  return total;
}

For apps with multiple screens, you'll need to implement navigation logic using the `Navigator` widget. Here's an example of navigating to a new screen:

Navigator.push(
  context,
  MaterialPageRoute(builder: (context) => SecondScreen()),
)

Remember the importance of managing state? When the state of your app changes due to user actions, data updates, or other events, you'll use `setState()` to trigger a rebuild of the UI.

Step 7: Testing Your App

(a) Unit Testing

(b) Widget Testing

(c) Integration Testing

(d) Writing Unit Tests

int add(int a, int b) {
  return a + b;
}

void main() {
  test('Adding numbers', () {
    expect(add(2, 3), equals(5));
    expect(add(0, 0), equals(0));
  });
}

(e) Writing Widget Tests

testWidgets('Counter increments', (WidgetTester tester) async {
  await tester.pumpWidget(MyApp());
  expect(find.text('0'), findsOneWidget);
  expect(find.text('1'), findsNothing);
  await tester.tap(find.byIcon(Icons.add));
  await tester.pump();
  expect(find.text('0'), findsNothing);
  expect(find.text('1'), findsOneWidget);
});

(f) Running Tests

flutter test

Step 8: Running Your App on Devices or Emulators

To test your app on a physical device, follow these steps:

flutter devices

flutter run -d 

If you don't have access to a physical device, you can test your app using an emulator. Flutter provides both Android and iOS emulators.

flutter run