Platform encapsulation

android/src/main/java/io/ably/flutter/plugin/AblyEventStreamHandler.java

@@ -154,7 +154,7 @@ public void onListen(Object object, EventChannel.EventSink uiThreadEventSink) {
           ablyLibrary.getRealtime(ablyMessage.handle).connection.on(connectionStateListener);
           break;
         case PlatformConstants.PlatformMethod.onRealtimeChannelStateChanged:
-          assert eventPayload != null : "event message is missing";
+          assert eventPayload != null : "onRealtimeChannelStateChanged: event message is missing";
           channelStateListener = new PluginChannelStateListener(eventSink);
           ablyLibrary
               .getRealtime(ablyMessage.handle)
@@ -163,7 +163,7 @@ public void onListen(Object object, EventChannel.EventSink uiThreadEventSink) {
               .on(channelStateListener);
           break;
         case PlatformConstants.PlatformMethod.onRealtimeChannelMessage:
-          assert eventPayload != null : "event message is missing";
+          assert eventPayload != null : "onRealtimeChannelMessage: event message is missing";
           try {
             channelMessageListener = new PluginChannelMessageListener(eventSink);
             ablyLibrary
@@ -176,7 +176,7 @@ public void onListen(Object object, EventChannel.EventSink uiThreadEventSink) {
           }
           break;
         case PlatformConstants.PlatformMethod.onRealtimePresenceMessage:
-          assert eventPayload != null : "event message is missing";
+          assert eventPayload != null : "onRealtimePresenceMessage: event message is missing";
           try {
             channelPresenceMessageListener = new PluginChannelPresenceMessageListener(eventSink);
             ablyLibrary
@@ -213,23 +213,23 @@ public void onCancel(Object object) {
       case PlatformConstants.PlatformMethod.onRealtimeChannelStateChanged:
         // Note: this and all other assert statements in this onCancel method are
         // left as is as there is no way of propagating this error to flutter side
-        assert eventPayload != null : "event message is missing";
+        assert eventPayload != null : "onRealtimeChannelStateChanged: event message is missing";
         ablyLibrary
             .getRealtime(ablyMessage.handle)
             .channels
             .get((String) eventPayload.get(PlatformConstants.TxTransportKeys.channelName))
             .off(channelStateListener);
         break;
       case PlatformConstants.PlatformMethod.onRealtimeChannelMessage:
-        assert eventPayload != null : "event message is missing";
+        assert eventPayload != null : "onRealtimeChannelMessage: event message is missing";
         ablyLibrary
             .getRealtime(ablyMessage.handle)
             .channels
             .get((String) eventPayload.get(PlatformConstants.TxTransportKeys.channelName))
             .unsubscribe(channelMessageListener);
         break;
       case PlatformConstants.PlatformMethod.onRealtimePresenceMessage:
-        assert eventPayload != null : "event message is missing";
+        assert eventPayload != null : "onRealtimePresenceMessage: event message is missing";
         ablyLibrary
             .getRealtime(ablyMessage.handle)
             .channels

lib/src/crypto/src/crypto.dart

@@ -32,7 +32,7 @@ class Crypto {
       throw AblyException(keyTypeErrorMessage);
     }
 
-    return Platform.invokePlatformMethodNonNull<CipherParams>(
+    return Platform().invokePlatformMethodNonNull<CipherParams>(
         PlatformMethod.cryptoGetParams, {
       TxCryptoGetParams.algorithm: defaultAlgorithm,
       TxCryptoGetParams.key: key,
@@ -55,6 +55,6 @@ class Crypto {
   /// this key with other clients, there is no way to decrypt the messages.
   static Future<Uint8List> generateRandomKey(
           {keyLength = defaultKeyLengthInBits}) =>
-      Platform.invokePlatformMethodNonNull<Uint8List>(
+      Platform().invokePlatformMethodNonNull<Uint8List>(
           PlatformMethod.cryptoGenerateRandomKey, keyLength);
 }

lib/src/platform/src/background_android_isolate_platform.dart

@@ -11,16 +11,11 @@ import 'package:flutter/services.dart';
 /// called when a separate isolate is launched by the app, not for apps
 /// launched with Activity.
 class BackgroundIsolateAndroidPlatform {
-  /// Instantiates if required.
-  factory BackgroundIsolateAndroidPlatform() {
-    _platform ??= BackgroundIsolateAndroidPlatform._internal();
-    return _platform!;
-  }
-
-  static BackgroundIsolateAndroidPlatform? _platform;
+  BackgroundIsolateAndroidPlatform._internal();
 
-  BackgroundIsolateAndroidPlatform._internal() {
-    methodChannel.setMethodCallHandler((call) async {
+  /// Start listening to messages from Java side.
+  void setupCallHandler() {
+    _methodChannel.setMethodCallHandler((call) async {
       switch (call.method) {
         case PlatformMethod.pushOnBackgroundMessage:
           return _onPushBackgroundMessage(call.arguments as RemoteMessage);
@@ -31,16 +26,25 @@ class BackgroundIsolateAndroidPlatform {
     });
   }
 
+  static final BackgroundIsolateAndroidPlatform _platform =
+      BackgroundIsolateAndroidPlatform._internal();
+
+  /// Singleton instance of BackgroundIsolateAndroidPlatform
+  factory BackgroundIsolateAndroidPlatform() => _platform;
+
   /// A method channel used to communicate with the user's app isolate
   /// we explicitly launched when a RemoteMessage is received.
   /// Used only on Android.
-  static final MethodChannel methodChannel =
-      MethodChannel('io.ably.flutter.plugin.background', Platform.codec);
+  final MethodChannel _methodChannel = MethodChannel(
+      'io.ably.flutter.plugin.background', StandardMethodCodec(Codec()));
 
   final PushNotificationEventsNative _pushNotificationEvents =
       PushNative.notificationEvents as PushNotificationEventsNative;
 
   Future<Object?> _onPushBackgroundMessage(RemoteMessage remoteMessage) async {
     _pushNotificationEvents.handleBackgroundMessage(remoteMessage);
   }
+
+  Future<T?> invokeMethod<T>(String method, [arguments]) async =>
+      _methodChannel.invokeMethod<T>(method, arguments);
 }

lib/src/platform/src/info.dart

@@ -2,10 +2,9 @@ import 'package:ably_flutter/ably_flutter.dart';
 import 'package:ably_flutter/src/platform/platform_internal.dart';
 
 /// Get android/iOS platform version
-Future<String> platformVersion() async =>
-    (await Platform.invokePlatformMethod<String>(
-        PlatformMethod.getPlatformVersion))!;
+Future<String> platformVersion() async => Platform()
+    .invokePlatformMethodNonNull<String>(PlatformMethod.getPlatformVersion);
 
 /// Get ably library version
 Future<String> version() async =>
-    (await Platform.invokePlatformMethod<String>(PlatformMethod.getVersion))!;
+    Platform().invokePlatformMethodNonNull<String>(PlatformMethod.getVersion);

lib/src/platform/src/method_call_handler.dart

@@ -32,7 +32,8 @@ class AblyMethodCallHandler {
           return onOpenSettingsFor();
         default:
           throw PlatformException(
-              code: 'invalid_method', message: 'No such method ${call.method}');
+              code: 'Received invalid method channel call from Platform side',
+              message: 'No such method ${call.method}');
       }
     });
   }

lib/src/platform/src/platform.dart

@@ -5,55 +5,49 @@ import 'package:ably_flutter/src/platform/platform_internal.dart';
 import 'package:flutter/services.dart';
 
 class Platform {
+  Platform._internal({MethodChannel? methodChannel}) {
+    _methodChannel = methodChannel;
+    if (methodChannel == null) {
+      _methodChannel = MethodChannel('io.ably.flutter.plugin', _codec);
+    }
+    _streamsChannel = StreamsChannel('io.ably.flutter.stream', _codec);
+    AblyMethodCallHandler(_methodChannel!);
+    BackgroundIsolateAndroidPlatform().setupCallHandler();
+    invokePlatformMethod(PlatformMethod.resetAblyClients);
+  }
+
+  static Platform? _platform;
+
+  /// Singleton instance of Platform
+  factory Platform({MethodChannel? methodChannel}) =>
+      _platform ??= Platform._internal(methodChannel: methodChannel);
+
   /// instance of [StandardMethodCodec] with custom [MessageCodec] for
   /// exchanging Ably types with platform via platform channels
   /// viz., [MethodChannel] and [StreamsChannel]
-  static StandardMethodCodec codec = StandardMethodCodec(Codec());
+  final StandardMethodCodec _codec = StandardMethodCodec(Codec());
 
   /// instance of method channel to interact with android/ios code
-  static final MethodChannel methodChannel =
-      MethodChannel('io.ably.flutter.plugin', codec);
+  MethodChannel? _methodChannel;
 
   /// instance of method channel to listen to android/ios events
-  static final StreamsChannel streamsChannel =
-      StreamsChannel('io.ably.flutter.stream', codec);
-
-  /// This field will be set to true when the app is restarted or
-  /// launched. This allows us to detect if an app has been restarted,
-  /// or a hot restart (not hot reload) has happened.
-  static bool _shouldResetAblyClients = true;
+  late final StreamsChannel? _streamsChannel;
 
-  /// Clears instances on the Platform side
-  static Future<void> _resetOldAblyClients() async {
-    if (_shouldResetAblyClients) {
-      AblyMethodCallHandler(methodChannel);
-      BackgroundIsolateAndroidPlatform();
-      await methodChannel.invokeMethod(PlatformMethod.resetAblyClients);
-      _shouldResetAblyClients = false;
-    }
-  }
-
-  /// invokes a platform [method] with [arguments]
-  ///
-  /// calls [_resetOldAblyClients] before invoking any method to handle any
-  /// cleanup tasks that are especially required while performing hot-restart
-  /// (as hot-restart does not automatically reset platform instances)
-  static Future<T?> invokePlatformMethod<T>(String method,
-      [Object? arguments]) async {
-    await _resetOldAblyClients();
+  Future<T?> invokePlatformMethod<T>(String method, [Object? arguments]) async {
     try {
-      return await methodChannel.invokeMethod<T>(method, arguments);
-    } on PlatformException catch (pe) {
-      if (pe.details is ErrorInfo) {
-        throw AblyException.fromPlatformException(pe);
+      return await _methodChannel!.invokeMethod<T>(method, arguments);
+    } on PlatformException catch (platformException) {
+      // Convert some PlatformExceptions into AblyException
+      if (platformException.details is ErrorInfo) {
+        throw AblyException.fromPlatformException(platformException);
       } else {
         rethrow;
       }
     }
   }
 
   /// Call a platform method which always provides a result.
-  static Future<T> invokePlatformMethodNonNull<T>(String method,
+  Future<T> invokePlatformMethodNonNull<T>(String method,
       [Object? arguments]) async {
     final result = await invokePlatformMethod<T>(method, arguments);
     if (result == null) {
@@ -63,4 +57,13 @@ class Platform {
       return result;
     }
   }
+
+  Stream<T> receiveBroadcastStream<T>(String methodName, int handle,
+          [final Object? payload]) =>
+      _streamsChannel!.receiveBroadcastStream<T>(
+        AblyMessage(
+          AblyEventMessage(methodName, payload),
+          handle: handle,
+        ),
+      );
 }

lib/src/platform/src/platform_object.dart

@@ -4,11 +4,10 @@ import 'package:ably_flutter/ably_flutter.dart';
 import 'package:flutter/services.dart';
 import 'package:meta/meta.dart';
 
-/// An object which has a live counterpart in the Platform client library SDK,
-/// where that live counterpart is held as a strong reference by the plugin
-/// implementation.
+/// A representation of a Platform side instance (Android, iOS).
 abstract class PlatformObject {
   Future<int>? _handle;
+  final Platform _platform = Platform();
   int? _handleValue; // Only for logging. Otherwise use _handle instead.
 
   /// immediately instantiates an object on platform side by calling
@@ -22,7 +21,7 @@ abstract class PlatformObject {
   }
 
   @override
-  String toString() => 'Ably Platform Object $_handleValue';
+  String toString() => 'Ably Flutter PlatformObject with handle: $_handleValue';
 
   /// creates an instance of this object on platform side
   Future<int?> createPlatformInstance();
@@ -36,19 +35,13 @@ abstract class PlatformObject {
   Future<int> _acquireHandle() =>
       createPlatformInstance().then((value) => (_handleValue = value)!);
 
-  /// [MethodChannel] to make method calls to platform side
-  MethodChannel get methodChannel => Platform.methodChannel;
-
-  /// [EventChannel] to register events on platform side
-  StreamsChannel get eventChannel => Platform.streamsChannel;
-
   /// invoke platform method channel without AblyMessage encapsulation
   @protected
   Future<T?> invokeRaw<T>(
     final String method, [
     final Object? arguments,
   ]) async =>
-      Platform.invokePlatformMethod<T>(method, arguments);
+      _platform.invokePlatformMethod<T>(method, arguments);
 
   /// invoke platform method channel with AblyMessage encapsulation
   ///
@@ -74,23 +67,15 @@ abstract class PlatformObject {
     return invokeRaw<T>(method, message);
   }
 
-  Future<Stream<T>> _listen<T>(
-    final String eventName, [
-    final Object? payload,
-  ]) async =>
-      eventChannel.receiveBroadcastStream<T>(
-        AblyMessage(
-          AblyEventMessage(eventName, payload),
-          handle: await handle,
-        ),
-      );
-
   /// Listen for events
   @protected
   Stream<T> listen<T>(final String method, [final Object? payload]) {
     // ignore: close_sinks, will be closed by listener
     final controller = StreamController<T>();
-    _listen<T>(method, payload).then(controller.addStream);
+    handle
+        .then((handle) =>
+            _platform.receiveBroadcastStream<T>(method, handle, payload))
+        .then(controller.addStream);
     return controller.stream;
   }
 }

lib/src/platform/src/push_notification_events_native.dart

@@ -18,7 +18,7 @@ class PushNotificationEventsNative implements PushNotificationEvents {
 
   @override
   Future<RemoteMessage?> get notificationTapLaunchedAppFromTerminated =>
-      Platform.methodChannel.invokeMethod(
+      Platform().invokePlatformMethod<RemoteMessage>(
           PlatformMethod.pushNotificationTapLaunchedAppFromTerminated);
 
   @override
@@ -56,7 +56,9 @@ class PushNotificationEventsNative implements PushNotificationEvents {
   Future<void> setOnBackgroundMessage(BackgroundMessageHandler handler) async {
     _onBackgroundMessage = handler;
     if (io.Platform.isAndroid) {
-      await BackgroundIsolateAndroidPlatform.methodChannel.invokeMethod(
+      // Inform Android side that the Flutter application
+      // is ready to receive push messages.
+      await BackgroundIsolateAndroidPlatform().invokeMethod(
           PlatformMethod.pushBackgroundFlutterApplicationReadyOnAndroid);
     }
   }

lib/src/platform/src/realtime/realtime.dart

@@ -43,8 +43,7 @@ class Realtime extends PlatformObject {
       // If this happens, we won't be able to identify which realtime client
       // the authCallback belongs to. Instead, on Android, we set autoConnect
       // to false, and call connect immediately once we get the handle.
-      await Platform.invokePlatformMethod(
-          PlatformMethod.connectRealtime, handle);
+      await invokeRaw(PlatformMethod.connectRealtime, handle);
     }
     return handle;
   }

test/ably_flutter_plugin_test.dart

@@ -1,9 +1,11 @@
 import 'package:ably_flutter/ably_flutter.dart';
 import 'package:ably_flutter/src/platform/platform_internal.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  final channel = Platform.methodChannel;
+  final channel =
+      MethodChannel('io.ably.flutter.plugin', StandardMethodCodec(Codec()));
 
   TestWidgetsFlutterBinding.ensureInitialized();
   var counter = 0;
@@ -33,6 +35,7 @@ void main() {
           return null;
       }
     });
+    Platform(methodChannel: channel);
   });
 
   tearDown(() {