Improve callback handling and self-destroying

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.6.1 - 2025-07-17
+- Fixed callback being called once in Android (improved handling) (#91)
+- Fixed "FlutterJNI.loadLibrary/prefetchDefaultFontManager/init called more than once"
+
 ## 1.6.0 - 2025-05-06
 - Updated to use the modern FlutterPlugin.FlutterPluginBinding pattern
 - Deprecated Registrar, PluginRegistrantCallback, and ShimPluginRegistry usage

android/src/main/kotlin/com/icapps/background_location_tracker/BackgroundLocationTrackerPlugin.kt

@@ -42,6 +42,9 @@ class BackgroundLocationTrackerPlugin : FlutterPlugin, MethodCallHandler, Activi
         channel?.setMethodCallHandler(null)
         channel = null
         applicationContext = null
+
+        // Clean up the background manager when plugin is detached
+        FlutterBackgroundManager.cleanup()
     }
 
     override fun onMethodCall(call: MethodCall, result: Result) {
@@ -73,6 +76,7 @@ class BackgroundLocationTrackerPlugin : FlutterPlugin, MethodCallHandler, Activi
 
         // New static properties for background execution
         private var flutterEngine: FlutterEngine? = null
+        private var isEngineInitialized = false
 
         // For compatibility with older plugins
         @Deprecated("Use FlutterEngine's plugin registry instead")
@@ -87,9 +91,42 @@ class BackgroundLocationTrackerPlugin : FlutterPlugin, MethodCallHandler, Activi
         // Method to get or create the Flutter engine for background execution
         @JvmStatic
         fun getFlutterEngine(context: Context): FlutterEngine {
-            return flutterEngine ?: FlutterEngine(context).also {
-                flutterEngine = it
-                pluginRegistrantCallback?.invoke(it)
+            synchronized(this) {
+                if (flutterEngine == null || !isEngineInitialized) {
+                    Logger.debug(TAG, "Creating new Flutter engine for background execution")
+                    flutterEngine = FlutterEngine(context).also { engine ->
+                        pluginRegistrantCallback?.invoke(engine)
+                        isEngineInitialized = true
+                        Logger.debug(TAG, "Flutter engine created and initialized")
+                    }
+                } else {
+                    Logger.debug(TAG, "Reusing existing Flutter engine")
+                }
+                return flutterEngine!!
+            }
+        }
+
+        // Method to properly cleanup the Flutter engine
+        @JvmStatic
+        fun cleanupFlutterEngine() {
+            synchronized(this) {
+                flutterEngine?.let { engine ->
+                    try {
+                        Logger.debug(TAG, "Cleaning up Flutter engine")
+                        // Stop the Dart isolate if it's running
+                        if (engine.dartExecutor.isExecutingDart) {
+                            engine.dartExecutor.onDetachedFromJNI()
+                        }
+                        // Destroy the engine
+                        engine.destroy()
+                        Logger.debug(TAG, "Flutter engine destroyed")
+                    } catch (e: Exception) {
+                        // Log the exception but don't crash
+                        Logger.debug(TAG, "Error during Flutter engine cleanup: ${e.message}")
+                    }
+                    flutterEngine = null
+                    isEngineInitialized = false
+                }
             }
         }
     }

android/src/main/kotlin/com/icapps/background_location_tracker/MethodCallHelper.kt

@@ -105,6 +105,7 @@ internal class MethodCallHelper(private val ctx: Context) : MethodChannel.Method
 
     private fun stopTracking(ctx: Context, call: MethodCall, result: MethodChannel.Result) {
         serviceConnection.service?.stopTracking()
+        FlutterBackgroundManager.cleanup()
         result.success(true)
     }
 

android/src/main/kotlin/com/icapps/background_location_tracker/flutter/FlutterBackgroundManager.kt

@@ -19,40 +19,124 @@ internal object FlutterBackgroundManager {
     private const val BACKGROUND_CHANNEL_NAME = "com.icapps.background_location_tracker/background_channel"
 
     private val flutterLoader = FlutterLoader()
+    private var backgroundChannel: MethodChannel? = null
+    private var isInitialized = false
+    private var pendingLocation: Location? = null
+    private var isSettingUp = false
 
     private fun getInitializedFlutterEngine(ctx: Context): FlutterEngine {
-        Logger.debug("BackgroundManager", "Creating new engine")
-
+        Logger.debug("BackgroundManager", "Getting Flutter engine")
         return BackgroundLocationTrackerPlugin.getFlutterEngine(ctx)
     }
 
     fun sendLocation(ctx: Context, location: Location) {
         Logger.debug("BackgroundManager", "Location: ${location.latitude}: ${location.longitude}")
-        val engine = getInitializedFlutterEngine(ctx)
+
+        if (isInitialized) {
+            // Engine is already initialized, send location immediately
+            sendLocationToChannel(ctx, location)
+        } else {
+            // Store the location and initialize if needed
+            pendingLocation = location
+            setupBackgroundChannelIfNeeded(ctx)
+        }
+    }
 
-        val backgroundChannel = MethodChannel(engine.dartExecutor, BACKGROUND_CHANNEL_NAME)
-        backgroundChannel.setMethodCallHandler { call, result ->
+    private fun setupBackgroundChannelIfNeeded(ctx: Context) {
+        if (backgroundChannel != null || isSettingUp) {
+            Logger.debug("BackgroundManager", "Setup already in progress or completed")
+            return // Already setup or in progress
+        }
+
+        isSettingUp = true
+        Logger.debug("BackgroundManager", "Setting up background channel and dart executor")
+        val engine = getInitializedFlutterEngine(ctx)
+
+        // Check if the DartExecutor is already running to prevent the error
+        if (engine.dartExecutor.isExecutingDart) {
+            Logger.debug("BackgroundManager", "DartExecutor is already running, reusing existing executor")
+            backgroundChannel = MethodChannel(engine.dartExecutor, BACKGROUND_CHANNEL_NAME)
+            backgroundChannel?.setMethodCallHandler { call, result ->
+                when (call.method) {
+                    "initialized" -> {
+                        Logger.debug("BackgroundManager", "Dart background isolate already initialized")
+                        isInitialized = true
+                        isSettingUp = false
+                        result.success(true)
+
+                        // Send any pending location
+                        pendingLocation?.let { location ->
+                            Logger.debug("BackgroundManager", "Sending pending location after reuse")
+                            sendLocationToChannel(ctx, location)
+                            pendingLocation = null
+                        }
+                    }
+                    else -> {
+                        result.notImplemented()
+                    }
+                }
+            }
+
+            // Mark as initialized since the executor is already running
+            isInitialized = true
+            isSettingUp = false
+
+            // Send any pending location immediately if we have one
+            pendingLocation?.let { location ->
+                Logger.debug("BackgroundManager", "Sending pending location immediately (executor already running)")
+                sendLocationToChannel(ctx, location)
+                pendingLocation = null
+            }
+
+            return
+        }
+
+        backgroundChannel = MethodChannel(engine.dartExecutor, BACKGROUND_CHANNEL_NAME)
+        backgroundChannel?.setMethodCallHandler { call, result ->
             when (call.method) {
-                "initialized" -> handleInitialized(call, result, ctx, backgroundChannel, location, engine)
+                "initialized" -> {
+                    Logger.debug("BackgroundManager", "Dart background isolate initialized")
+                    isInitialized = true
+                    isSettingUp = false
+                    result.success(true)
+
+                    // Send any pending location
+                    pendingLocation?.let { location ->
+                        Logger.debug("BackgroundManager", "Sending pending location after initialization")
+                        sendLocationToChannel(ctx, location)
+                        pendingLocation = null
+                    }
+                }
                 else -> {
                     result.notImplemented()
-                    engine.destroy()
                 }
             }
         }
 
         if (!flutterLoader.initialized()) {
+            Logger.debug("BackgroundManager", "Initializing FlutterLoader")
             flutterLoader.startInitialization(ctx)
         }
+
         flutterLoader.ensureInitializationCompleteAsync(ctx, null, Handler(Looper.getMainLooper())) {
+            Logger.debug("BackgroundManager", "FlutterLoader initialization complete, executing Dart callback")
             val callbackHandle = SharedPrefsUtil.getCallbackHandle(ctx)
             val callbackInfo = FlutterCallbackInformation.lookupCallbackInformation(callbackHandle)
             val dartBundlePath = flutterLoader.findAppBundlePath()
-            engine.dartExecutor.executeDartCallback(DartExecutor.DartCallback(ctx.assets, dartBundlePath, callbackInfo))
+
+            try {
+                engine.dartExecutor.executeDartCallback(DartExecutor.DartCallback(ctx.assets, dartBundlePath, callbackInfo))
+            } catch (e: Exception) {
+                Logger.debug("BackgroundManager", "Error executing Dart callback: ${e.message}")
+                isSettingUp = false
+            }
         }
     }
 
-    private fun handleInitialized(call: MethodCall, result: MethodChannel.Result, ctx: Context, channel: MethodChannel, location: Location, engine: FlutterEngine) {
+    private fun sendLocationToChannel(ctx: Context, location: Location) {
+        val channel = backgroundChannel ?: return
+        Logger.debug("BackgroundManager", "Sending location to initialized channel")
+
         val data = mutableMapOf<String, Any>()
         data["lat"] = location.latitude
         data["lon"] = location.longitude
@@ -73,19 +157,37 @@ internal object FlutterBackgroundManager {
 
         channel.invokeMethod("onLocationUpdate", data, object : MethodChannel.Result {
             override fun success(result: Any?) {
-                Logger.debug("BackgroundManager", "Got success, destroy engine!")
-                engine.destroy()
+                Logger.debug("BackgroundManager", "Successfully sent location update")
             }
 
             override fun error(errorCode: String, errorMessage: String?, errorDetails: Any?) {
-                Logger.debug("BackgroundManager", "Got error, destroy engine! $errorCode - $errorMessage : $errorDetails")
-                engine.destroy()
+                Logger.debug("BackgroundManager", "Error sending location update: $errorCode - $errorMessage : $errorDetails")
             }
 
             override fun notImplemented() {
-                Logger.debug("BackgroundManager", "Got not implemented, destroy engine!")
-                engine.destroy()
+                Logger.debug("BackgroundManager", "Method not implemented for location update")
             }
         })
     }
-}
+
+    fun cleanup() {
+        Logger.debug("BackgroundManager", "Cleaning up background resources")
+        isInitialized = false
+        isSettingUp = false
+        backgroundChannel?.setMethodCallHandler(null)
+        backgroundChannel = null
+        pendingLocation = null
+
+        // Instead of destroying the engine completely, just mark it as not initialized
+        // This allows for reuse without the "DartExecutor already running" error
+        Logger.debug("BackgroundManager", "Background channel cleaned up, ready for reuse")
+    }
+
+    fun forceCleanup() {
+        Logger.debug("BackgroundManager", "Force cleaning up all background resources")
+        cleanup()
+
+        // Clean up the Flutter engine completely to prevent DartExecutor reuse issues
+        BackgroundLocationTrackerPlugin.cleanupFlutterEngine()
+    }
+}

android/src/main/kotlin/com/icapps/background_location_tracker/service/LocationUpdatesService.kt

@@ -160,6 +160,9 @@ internal class LocationUpdatesService : Service() {
         if (wakeLock?.isHeld == true) {
             wakeLock?.release()
         }
+
+        // Force clean up Flutter background resources when service is destroyed
+        FlutterBackgroundManager.forceCleanup()
     }
 
     /**

example/pubspec.lock

@@ -13,17 +13,17 @@ packages:
     dependency: transitive
     description:
       name: async
-      sha256: d2872f9c19731c2e5f10444b14686eb7cc85c76274bd6c16e1816bff9a3bab63
+      sha256: "758e6d74e971c3e5aceb4110bfd6698efc7f501675bcfe0c775459a8140750eb"
       url: "https://pub.dev"
     source: hosted
-    version: "2.12.0"
+    version: "2.13.0"
   background_location_tracker:
     dependency: "direct main"
     description:
       path: ".."
       relative: true
     source: path
-    version: "1.5.0"
+    version: "1.6.0"
   boolean_selector:
     dependency: transitive
     description:
@@ -68,10 +68,10 @@ packages:
     dependency: transitive
     description:
       name: fake_async
-      sha256: "6a95e56b2449df2273fd8c45a662d6947ce1ebb7aafe80e550a3f68297f3cacc"
+      sha256: "5368f224a74523e8d2e7399ea1638b37aecfca824a3cc4dfdf77bf1fa905ac44"
       url: "https://pub.dev"
     source: hosted
-    version: "1.3.2"
+    version: "1.3.3"
   ffi:
     dependency: transitive
     description:
@@ -155,10 +155,10 @@ packages:
     dependency: transitive
     description:
       name: leak_tracker
-      sha256: c35baad643ba394b40aac41080300150a4f08fd0fd6a10378f8f7c6bc161acec
+      sha256: "6bb818ecbdffe216e81182c2f0714a2e62b593f4a4f13098713ff1685dfb6ab0"
       url: "https://pub.dev"
     source: hosted
-    version: "10.0.8"
+    version: "10.0.9"
   leak_tracker_flutter_testing:
     dependency: transitive
     description:
@@ -456,10 +456,10 @@ packages:
     dependency: transitive
     description:
       name: vm_service
-      sha256: "0968250880a6c5fe7edc067ed0a13d4bae1577fe2771dcf3010d52c4a9d3ca14"
+      sha256: ddfa8d30d89985b96407efce8acbdd124701f96741f2d981ca860662f1c0dc02
       url: "https://pub.dev"
     source: hosted
-    version: "14.3.1"
+    version: "15.0.0"
   web:
     dependency: transitive
     description:

pubspec.lock

@@ -5,10 +5,10 @@ packages:
     dependency: transitive
     description:
       name: async
-      sha256: d2872f9c19731c2e5f10444b14686eb7cc85c76274bd6c16e1816bff9a3bab63
+      sha256: "758e6d74e971c3e5aceb4110bfd6698efc7f501675bcfe0c775459a8140750eb"
       url: "https://pub.dev"
     source: hosted
-    version: "2.12.0"
+    version: "2.13.0"
   boolean_selector:
     dependency: transitive
     description:
@@ -45,10 +45,10 @@ packages:
     dependency: transitive
     description:
       name: fake_async
-      sha256: "6a95e56b2449df2273fd8c45a662d6947ce1ebb7aafe80e550a3f68297f3cacc"
+      sha256: "5368f224a74523e8d2e7399ea1638b37aecfca824a3cc4dfdf77bf1fa905ac44"
       url: "https://pub.dev"
     source: hosted
-    version: "1.3.2"
+    version: "1.3.3"
   flutter:
     dependency: "direct main"
     description: flutter
@@ -63,10 +63,10 @@ packages:
     dependency: transitive
     description:
       name: leak_tracker
-      sha256: c35baad643ba394b40aac41080300150a4f08fd0fd6a10378f8f7c6bc161acec
+      sha256: "6bb818ecbdffe216e81182c2f0714a2e62b593f4a4f13098713ff1685dfb6ab0"
       url: "https://pub.dev"
     source: hosted
-    version: "10.0.8"
+    version: "10.0.9"
   leak_tracker_flutter_testing:
     dependency: transitive
     description:
@@ -180,10 +180,10 @@ packages:
     dependency: transitive
     description:
       name: vm_service
-      sha256: "0968250880a6c5fe7edc067ed0a13d4bae1577fe2771dcf3010d52c4a9d3ca14"
+      sha256: ddfa8d30d89985b96407efce8acbdd124701f96741f2d981ca860662f1c0dc02
       url: "https://pub.dev"
     source: hosted
-    version: "14.3.1"
+    version: "15.0.0"
 sdks:
   dart: ">=3.7.0-0 <4.0.0"
   flutter: ">=3.18.0-18.0.pre.54"