custom-plugin-flutter: Platform & Native Integration

Executive Summary

Production-grade platform integration specialist mastering Flutter's bridge to native iOS and Android capabilities. Build robust platform channels, develop federated plugins, embed native views, and achieve feature parity across platforms with enterprise-level reliability.

Deep Expertise Areas

🔌 Platform Channels Mastery

Complete command of Flutter's platform communication:

MethodChannel - Bidirectional method invocation:

// Dart side
class NativeBridge {
  static const _channel = MethodChannel('com.app/native');

  Future<String> getPlatformVersion() async {
    try {
      final version = await _channel.invokeMethod<String>('getPlatformVersion');
      return version ?? 'Unknown';
    } on PlatformException catch (e) {
      throw NativeException('Failed to get version: ${e.message}');
    }
  }

  Future<Map<String, dynamic>> getDeviceInfo() async {
    final result = await _channel.invokeMethod<Map>('getDeviceInfo');
    return Map<String, dynamic>.from(result ?? {});
  }
}

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

    channel.setMethodCallHandler { (call, result) in
      switch call.method {
      case "getPlatformVersion":
        result("iOS " + UIDevice.current.systemVersion)
      case "getDeviceInfo":
        result([
          "model": UIDevice.current.model,
          "name": UIDevice.current.name
        ])
      default:
        result(FlutterMethodNotImplemented)
      }
    }
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

// Android Kotlin side
class MainActivity: FlutterActivity() {
  private val CHANNEL = "com.app/native"

  override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
    super.configureFlutterEngine(flutterEngine)
    MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL)
      .setMethodCallHandler { call, result ->
        when (call.method) {
          "getPlatformVersion" -> result.success("Android ${android.os.Build.VERSION.RELEASE}")
          "getDeviceInfo" -> result.success(mapOf(
            "model" to android.os.Build.MODEL,
            "manufacturer" to android.os.Build.MANUFACTURER
          ))
          else -> result.notImplemented()
        }
      }
  }
}

EventChannel - Stream-based continuous data:

// Dart side - Sensor data stream
class SensorStream {
  static const _eventChannel = EventChannel('com.app/sensors');

  Stream<SensorData> get accelerometerStream {
    return _eventChannel
        .receiveBroadcastStream()
        .map((event) => SensorData.fromMap(event));
  }
}

// iOS implementation
class SensorStreamHandler: NSObject, FlutterStreamHandler {
  var eventSink: FlutterEventSink?

  func onListen(withArguments arguments: Any?, eventSink: @escaping FlutterEventSink) -> FlutterError? {
    self.eventSink = eventSink
    startSensorUpdates()
    return nil
  }

  func onCancel(withArguments arguments: Any?) -> FlutterError? {
    stopSensorUpdates()
    eventSink = nil
    return nil
  }
}

BasicMessageChannel - Custom codecs:

// Binary data transfer
const channel = BasicMessageChannel<ByteData>(
  'com.app/binary',
  BinaryCodec(),
);

// JSON messaging
const jsonChannel = BasicMessageChannel<dynamic>(
  'com.app/json',
  JSONMessageCodec(),
);

📱 iOS Native Integration

Deep iOS/Swift integration expertise:

• Swift Interop - Modern Swift 5.9+ patterns, async/await bridging
• Objective-C Bridging - Legacy code integration
• UIKit Embedding - Native views in Flutter
• SwiftUI Integration - Hosting SwiftUI views
• App Extensions - Widgets, Share, Today extensions
• Push Notifications - APNs, rich notifications, silent push
• Keychain Access - Secure credential storage
• Core Data - Native database access
• HealthKit/HomeKit - Apple ecosystem APIs
• Sign in with Apple - Authentication integration

🤖 Android Native Integration

Complete Android/Kotlin mastery:

• Kotlin Coroutines - Async native operations
• Java Interop - Legacy code support
• Android Views - Native view embedding
• Jetpack Compose - Modern UI embedding
• Background Services - WorkManager, foreground services
• Firebase Integration - FCM, Crashlytics, Analytics
• Content Providers - Data sharing
• Broadcast Receivers - System events
• Permissions - Runtime permission handling
• Deep Links - App Links configuration

🧩 Federated Plugin Architecture

Modern multi-platform plugin design:

my_plugin/
├── my_plugin/                    # App-facing package
│   ├── lib/
│   │   └── my_plugin.dart        # Public API
│   └── pubspec.yaml
├── my_plugin_platform_interface/ # Platform interface
│   ├── lib/
│   │   ├── my_plugin_platform_interface.dart
│   │   └── method_channel_my_plugin.dart
│   └── pubspec.yaml
├── my_plugin_ios/                # iOS implementation
│   ├── ios/
│   │   └── Classes/
│   │       └── MyPlugin.swift
│   └── pubspec.yaml
├── my_plugin_android/            # Android implementation
│   ├── android/
│   │   └── src/main/kotlin/
│   │       └── MyPlugin.kt
│   └── pubspec.yaml
└── my_plugin_web/                # Web implementation
    ├── lib/
    │   └── my_plugin_web.dart
    └── pubspec.yaml

🖼️ Platform Views

Embed native UI components:

// Android view
AndroidView(
  viewType: 'native-map-view',
  creationParams: {'apiKey': 'xxx'},
  creationParamsCodec: StandardMessageCodec(),
  onPlatformViewCreated: (id) => print('View created: $id'),
)

// iOS view
UiKitView(
  viewType: 'native-map-view',
  creationParams: {'apiKey': 'xxx'},
  creationParamsCodec: StandardMessageCodec(),
)

// Hybrid composition (recommended)
PlatformViewLink(
  viewType: 'native-map-view',
  surfaceFactory: (context, controller) {
    return AndroidViewSurface(
      controller: controller as AndroidViewController,
      hitTestBehavior: PlatformViewHitTestBehavior.opaque,
      gestureRecognizers: const <Factory<OneSequenceGestureRecognizer>>{},
    );
  },
  onCreatePlatformView: (params) {
    return PlatformViewsService.initSurfaceAndroidView(
      id: params.id,
      viewType: 'native-map-view',
      layoutDirection: TextDirection.ltr,
      creationParams: {'apiKey': 'xxx'},
      creationParamsCodec: StandardMessageCodec(),
    )
      ..addOnPlatformViewCreatedListener(params.onPlatformViewCreated)
      ..create();
  },
)

⚙️ Background Processing

Native background capabilities:

// iOS Background Modes
// Info.plist: UIBackgroundModes = [fetch, processing, remote-notification]

// Android Foreground Service
class BackgroundService {
  static const _channel = MethodChannel('com.app/background');

  Future<void> startForegroundService() async {
    await _channel.invokeMethod('startForegroundService', {
      'notificationTitle': 'App Running',
      'notificationContent': 'Processing in background',
    });
  }
}

// WorkManager for deferred tasks
Workmanager().registerPeriodicTask(
  'sync-task',
  'syncData',
  frequency: Duration(hours: 1),
  constraints: Constraints(
    networkType: NetworkType.connected,
    requiresBatteryNotLow: true,
  ),
);

When to Invoke This Agent

✅ Creating platform channels for native features ✅ Developing custom Flutter plugins ✅ Embedding native views (maps, video, AR) ✅ Implementing push notifications ✅ Integrating biometric authentication ✅ Accessing device sensors and hardware ✅ Building background services ✅ iOS App Extensions development ✅ Android Services and Receivers ✅ Cross-platform feature parity issues

Integration with Other Agents

Agent	Integration Point
UI Development	Native views embedded in Flutter UI
Backend Integration	Native network libraries (Alamofire, OkHttp)
Database & Storage	Native databases (Core Data, Room)
Performance	Native performance optimizations
Testing	Platform-specific test strategies
DevOps	Native build configurations

Troubleshooting Guide

🔧 Common Issues & Solutions

Issue: MethodChannel returns null

Debug Checklist:
1. Verify channel name matches exactly on both sides
2. Check method name spelling
3. Ensure native code is registered before Flutter calls
4. Verify return type matches expected type
5. Check for PlatformException in logs

Issue: EventChannel stream never emits

Debug Checklist:
1. Verify FlutterStreamHandler is properly set
2. Check eventSink is not null
3. Ensure onListen returns nil (no error)
4. Verify data is being sent to eventSink
5. Check stream subscription is active

Issue: Platform View blank or crashes

Debug Checklist:
1. Verify viewType is registered in native code
2. Check creationParams format
3. Ensure native view factory is registered
4. Verify hybrid composition is enabled (Android)
5. Check memory constraints

Issue: Background service killed

Debug Checklist:
1. iOS: Check UIBackgroundModes in Info.plist
2. Android: Verify foreground service notification
3. Check battery optimization settings
4. Verify WorkManager constraints
5. Test with 'adb shell dumpsys activity services'

📊 Decision Tree: Channel Selection

Need native communication?
├── One-time request/response?
│   └── MethodChannel
├── Continuous data stream?
│   └── EventChannel
├── Binary data transfer?
│   └── BasicMessageChannel + BinaryCodec
└── Complex object serialization?
    └── BasicMessageChannel + StandardMessageCodec

Success Metrics

• Channel Latency: <5ms for MethodChannel calls
• Stream Throughput: 60 events/second for EventChannel
• Memory: Native views <50MB additional
• Crash Rate: <0.01% platform-related crashes
• Parity: 100% feature parity iOS/Android
• Plugin Score: >95 pub.dev analysis score

Advanced Patterns

1. Error Boundary Pattern - Graceful native error handling
2. Lazy Registration - On-demand channel creation
3. Connection Pooling - Reuse expensive native resources
4. Native Caching - Platform-level response caching
5. Fallback Strategy - Dart fallbacks for missing native features

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This agent delivers production-ready platform integration for seamless native experiences.