🔌 Platform-specific Code

1. Platform Detection

import 'dart:io';

if (Platform.isAndroid) {
  // Android code
} else if (Platform.isIOS) {
  // iOS code
} else if (Platform.isWindows) {
  // Windows code
} else if (Platform.isMacOS) {
  // macOS code
} else if (Platform.isLinux) {
  // Linux code
}

Với kIsWeb

import 'package:flutter/foundation.dart';

if (kIsWeb) {
  // Web code
} else if (Platform.isAndroid) {
  // Android code
}

---

2. Platform Widgets

Cupertino vs Material

import 'dart:io';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

Widget buildButton() {
  if (Platform.isIOS) {
    return CupertinoButton(
      onPressed: () {},
      child: Text('iOS Button'),
    );
  } else {
    return ElevatedButton(
      onPressed: () {},
      child: Text('Android Button'),
    );
  }
}

Platform-aware Widget

class PlatformButton extends StatelessWidget {
  final String text;
  final VoidCallback onPressed;

  const PlatformButton({
    super.key,
    required this.text,
    required this.onPressed,
  });

  @override
  Widget build(BuildContext context) {
    return Platform.isIOS
        ? CupertinoButton(
            onPressed: onPressed,
            child: Text(text),
          )
        : ElevatedButton(
            onPressed: onPressed,
            child: Text(text),
          );
  }
}

---

3. Platform Channels

Gọi native code từ Flutter:

Dart side

import 'package:flutter/services.dart';

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

  Future<int> getBatteryLevel() async {
    try {
      final result = await platform.invokeMethod('getBatteryLevel');
      return result as int;
    } on PlatformException catch (e) {
      throw Exception('Failed to get battery: ${e.message}');
    }
  }
}

Android (Kotlin)

MainActivity.kt

class MainActivity: FlutterActivity() {
    private val CHANNEL = "com.example.app/battery"

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)

        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL)
            .setMethodCallHandler { call, result ->
                if (call.method == "getBatteryLevel") {
                    val batteryLevel = getBatteryLevel()
                    if (batteryLevel != -1) {
                        result.success(batteryLevel)
                    } else {
                        result.error("UNAVAILABLE", "Battery level not available", null)
                    }
                } else {
                    result.notImplemented()
                }
            }
    }

    private fun getBatteryLevel(): Int {
        val batteryManager = getSystemService(BATTERY_SERVICE) as BatteryManager
        return batteryManager.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY)
    }
}

iOS (Swift)

AppDelegate.swift

@UIApplicationMain
class AppDelegate: FlutterAppDelegate {
    override func application(
        _ application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
    ) -> Bool {
        let controller = window?.rootViewController as! FlutterViewController
        let batteryChannel = FlutterMethodChannel(
            name: "com.example.app/battery",
            binaryMessenger: controller.binaryMessenger
        )

        batteryChannel.setMethodCallHandler { call, result in
            if call.method == "getBatteryLevel" {
                self.receiveBatteryLevel(result: result)
            } else {
                result(FlutterMethodNotImplemented)
            }
        }

        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    }

    private func receiveBatteryLevel(result: FlutterResult) {
        let device = UIDevice.current
        device.isBatteryMonitoringEnabled = true
        if device.batteryState == UIDevice.BatteryState.unknown {
            result(FlutterError(code: "UNAVAILABLE", message: "Battery unavailable", details: nil))
        } else {
            result(Int(device.batteryLevel * 100))
        }
    }
}

---

4. Conditional Imports

interface.dart

abstract class StorageService {
  Future<void> save(String key, String value);
  Future<String?> load(String key);
}

// storage_mobile.dart
import 'package:shared_preferences/shared_preferences.dart';
class StorageServiceImpl implements StorageService {
  Future<void> save(String key, String value) async {
    final prefs = await SharedPreferences.getInstance();
    await prefs.setString(key, value);
  }
  // ...
}

// storage_web.dart
import 'dart:html' as html;
class StorageServiceImpl implements StorageService {
  Future<void> save(String key, String value) async {
    html.window.localStorage[key] = value;
  }
  // ...
}

// storage.dart
export 'storage_stub.dart'
    if (dart.library.io) 'storage_mobile.dart'
    if (dart.library.html) 'storage_web.dart';

---

5. Platform-specific Permissions

Android

android/app/src/main/AndroidManifest.xml

<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.INTERNET" />

iOS

<!-- ios/Runner/Info.plist -->
<key>NSCameraUsageDescription</key>
<string>This app needs camera access</string>
<key>NSPhotoLibraryUsageDescription</key>
<string>This app needs photo library access</string>

---

6. Platform-specific UI Patterns

Back Button

// Android: Hardware back button
// iOS: Swipe gesture

// Customize với WillPopScope / PopScope
PopScope(
  canPop: false,
  onPopInvoked: (didPop) async {
    if (didPop) return;
    // Show confirmation
  },
  child: Scaffold(...),
)

Pull to Refresh

RefreshIndicator(
  onRefresh: _refresh,
  // Material style on Android, Cupertino style configurable
  child: ListView(...),
)

---

7. Theme theo Platform

ThemeData buildTheme() {
  if (Platform.isIOS) {
    return ThemeData(
      // iOS-like styling
      appBarTheme: AppBarTheme(
        backgroundColor: Colors.white,
        foregroundColor: Colors.black,
        elevation: 0,
      ),
    );
  } else {
    return ThemeData(
      // Material styling
      useMaterial3: true,
    );
  }
}

---

8. Plugin Packages

Nhiều packages xử lý platform-specific code cho bạn:

dependencies:
  # Camera
  camera: ^0.10.0

  # Image picker
  image_picker: ^1.0.0

  # Permissions
  permission_handler: ^11.0.0

  # Local storage
  shared_preferences: ^2.2.0

  # Device info
  device_info_plus: ^9.0.0

  # URL launcher
  url_launcher: ^6.2.0

---

📝 Tóm tắt

Approach	Khi nào dùng
Platform.isX	Simple platform checks
Platform widgets	Different UI per platform
Platform channels	Native features không có package
Conditional imports	Platform-specific implementations

Platform	Native Language
Android	Kotlin/Java
iOS	Swift/Objective-C
Web	JavaScript
Desktop	C++/Swift