Understanding the Architecture and Platform Differences When Developing Flutter Desktop Applications

Flutter, Google’s UI toolkit, has expanded beyond mobile development to support desktop platforms like Windows, macOS, and Linux. Developing Flutter desktop applications brings a new set of challenges and considerations compared to mobile. Understanding the architectural differences and platform-specific nuances is essential for building robust, efficient, and well-integrated desktop apps. This article delves into these differences to help you navigate desktop development with Flutter.

What are Flutter Desktop Applications?

Flutter desktop applications are standalone programs built using the Flutter framework that can run on desktop operating systems such as Windows, macOS, and Linux. Flutter’s cross-platform capabilities allow developers to write code once and deploy it to multiple platforms, making it an attractive option for desktop development.

Architecture Differences Between Mobile and Desktop

While the Flutter core remains consistent, there are notable architectural differences between mobile and desktop applications due to the underlying operating systems and their respective functionalities.

Operating System Interaction

• Mobile: Mobile operating systems like Android and iOS have a more controlled environment, with clear APIs for accessing device features, handling permissions, and managing resources.
• Desktop: Desktop operating systems provide a broader and more diverse set of APIs for interacting with the system. Direct access to system resources, hardware, and lower-level functionalities is more common.

Window Management

• Mobile: Mobile apps typically run in full-screen mode, with a single active screen (Activity in Android, ViewController in iOS). Window management is minimal and usually handled by the OS.
• Desktop: Desktop applications require more complex window management, including handling multiple windows, resizing, minimizing, maximizing, and custom window decorations.

Input Methods

• Mobile: Input is primarily touch-based, with additional sensors like accelerometers and gyroscopes.
• Desktop: Input relies on keyboard, mouse, trackpad, and other peripherals. Keyboard and mouse input require more sophisticated handling, including keyboard shortcuts, context menus, and mouse hover effects.

Resource Management

• Mobile: Mobile devices have limited resources, such as battery life, memory, and processing power. Mobile apps must be optimized to conserve these resources.
• Desktop: Desktop environments generally offer more abundant resources. However, efficient resource management is still crucial to prevent performance issues and ensure smooth operation, especially for complex applications.

Platform Differences

Despite Flutter’s cross-platform nature, differences between Windows, macOS, and Linux platforms can impact development. Here are some key distinctions:

Windows

• APIs: Windows applications rely on the Win32 API and newer Windows Runtime (WinRT) APIs. Interacting with these APIs directly from Flutter requires using Platform Channels or native plugins.
• Packaging: Windows applications are typically distributed as .exe files or through the Microsoft Store.
• UI/UX: Windows has its own UI/UX guidelines. Adhering to these guidelines helps create applications that feel native to the Windows environment.

macOS

• APIs: macOS applications use the Cocoa framework, which is based on Objective-C/Swift. Accessing macOS-specific features requires interacting with these frameworks.
• Packaging: macOS applications are packaged as .app bundles, which are essentially directories containing the application’s resources and executable.
• UI/UX: macOS has its own design language, emphasizing simplicity and elegance. Following the macOS Human Interface Guidelines is important for creating native-feeling apps.

Linux

• APIs: Linux applications can use various APIs depending on the distribution and desktop environment (e.g., GTK, Qt). The choice of API can affect the application’s appearance and behavior.
• Packaging: Linux applications are often distributed as packages (e.g., .deb for Debian-based systems, .rpm for Red Hat-based systems) or as AppImage, Snap, or Flatpak bundles.
• UI/UX: Linux offers a wide range of desktop environments (e.g., GNOME, KDE, XFCE), each with its own UI/UX conventions. Designing applications that integrate well with the user’s chosen environment is key.

Developing Flutter Desktop Applications: Key Considerations

When developing Flutter desktop applications, keep the following points in mind:

Platform Channels and Native Plugins

Flutter’s Platform Channels enable communication between Flutter code and native platform code. Native plugins provide a higher-level abstraction for accessing platform-specific features.

Example: Accessing Native API using Platform Channels (Kotlin – Android-style but applicable to Desktop)

// Dart code
import 'dart:io' show Platform;
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

class SystemInfo {
  static const platform = MethodChannel('com.example.app/system');

  Future getOperatingSystem() async {
    try {
      final String result = await platform.invokeMethod('getOS');
      return 'Operating system: $result';
    } on PlatformException catch (e) {
      return "Failed to get operating system: '${e.message}'.";
    }
  }
}

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State {
  String _osInfo = 'Press the button to get the OS info.';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Platform Channel Example')),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(_osInfo),
            ElevatedButton(
              onPressed: () async {
                SystemInfo().getOperatingSystem().then((value) => {
                  setState(() {
                    _osInfo = value;
                  })
                });
              },
              child: Text('Get OS Info'),
            ),
          ],
        ),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    title: 'Platform Channel Example',
    home: HomeScreen(),
  ));
}

// Kotlin (Desktop/Native side)
import io.flutter.plugin.common.MethodCall
import io.flutter.plugin.common.MethodChannel
import io.flutter.plugin.common.MethodChannel.MethodCallHandler
import io.flutter.plugin.common.MethodChannel.Result
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugins.GeneratedPluginRegistrant
import java.lang.System

class MainActivity {
    fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine)
        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, "com.example.app/system")
            .setMethodCallHandler { call: MethodCall, result: Result ->
                if (call.method == "getOS") {
                    val osName = System.getProperty("os.name")
                    result.success(osName)
                } else {
                    result.notImplemented()
                }
            }
    }
}

This Dart code invokes a method named getOS on the native side (platform), which retrieves the operating system name using Java’s System.getProperty("os.name") and returns the result to the Flutter app. This is just an illustrative and android based sample, platform channel code differs for all supported platforms.

Adaptive UI Design

Design your UI to adapt to different screen sizes and input methods. Consider using responsive layouts and providing options for both mouse/keyboard and touch input.

import 'package:flutter/material.dart';

class AdaptiveText extends StatelessWidget {
  final String text;

  const AdaptiveText(this.text, {Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    // Define different styles based on the screen width.
    TextStyle textStyle = (MediaQuery.of(context).size.width > 600)
        ? TextStyle(fontSize: 20, color: Colors.blue) // Larger screens
        : TextStyle(fontSize: 16, color: Colors.green); // Smaller screens

    return Text(text, style: textStyle);
  }
}

class AdaptiveLayout extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Adaptive Layout Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            AdaptiveText("This text will adapt based on the screen size."),
            // Other UI components
          ],
        ),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: AdaptiveLayout(),
  ));
}

Here, an adaptive layout provides different text styles (different fontsize) according to the platform used(mobile/desktop). The above dart sample provides fontsize more than “600” dp to the desktop and defaults to mobile

Window Management

Use plugins like window_manager to handle window-specific tasks such as setting window size, position, and title.

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

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await windowManager.ensureInitialized();

  WindowOptions windowOptions = const WindowOptions(
    size: Size(800, 600),
    center: true,
    backgroundColor: Colors.transparent,
    skipTaskbar: false,
    titleBarStyle: TitleBarStyle.normal,
  );

  windowManager.waitUntilReadyToShow(windowOptions, () async {
    await windowManager.show();
    await windowManager.focus();
  });

  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Window Manager Example'),
        ),
        body: const Center(
          child: Text('Flutter desktop app with window_manager'),
        ),
      ),
    );
  }
}

This Flutter code snippet demonstrates how to use the window_manager plugin to manage the app’s window on desktop platforms. It sets the initial window size to 800×600, centers it on the screen, makes the background transparent, prevents it from being hidden from the taskbar, and sets the title bar style to normal.

Keyboard Shortcuts and Mouse Input

Implement keyboard shortcuts using RawKeyboardListener and handle mouse input using MouseRegion and GestureDetector.

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

class KeyboardShortcutExample extends StatefulWidget {
  @override
  _KeyboardShortcutExampleState createState() => _KeyboardShortcutExampleState();
}

class _KeyboardShortcutExampleState extends State {
  String _keyPressInfo = 'Press Ctrl+S to trigger an action';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Keyboard Shortcut Example'),
      ),
      body: RawKeyboardListener(
        focusNode: FocusNode(),
        onKey: (event) {
          if (event is RawKeyDownEvent) {
            if (event.isControlPressed && event.logicalKey == LogicalKeyboardKey.keyS) {
              setState(() {
                _keyPressInfo = 'Ctrl+S was pressed!';
              });
            }
          }
        },
        child: Center(
          child: Text(_keyPressInfo),
        ),
      ),
    );
  }

  @override
  void initState() {
    super.initState();
    // Request focus to make sure the RawKeyboardListener is listening.
    FocusScope.of(context).requestFocus(FocusNode());
  }
}

void main() {
  runApp(MaterialApp(
    home: KeyboardShortcutExample(),
  ));
}

The RawKeyboardListener is used to capture keyboard events in the app, allowing the application to perform an action with `CTRL+S` in any keyboard event.

UI/UX Considerations

Follow the UI/UX guidelines for each platform to create applications that feel native. This includes using appropriate widgets, icons, and interaction patterns.

Conclusion

Developing Flutter desktop applications requires understanding the architectural and platform differences compared to mobile development. By leveraging Platform Channels, native plugins, adaptive UI design, and platform-specific APIs, you can create high-quality desktop apps that seamlessly integrate with Windows, macOS, and Linux environments. Keep these considerations in mind to ensure your Flutter desktop apps provide a native-like experience on each platform, maximizing their usability and appeal.