Unhandled Exception: MissingPluginException(No implementation found for method...) - flutter

Question

I have an existing Flutter app that I use to prototype and test ideas before adding the idea to a project. I need a custom plugin to track location in the background for a project so I added plugin related code into the normal app project.
I am targeting android for a start. I have a Dart class representing the plugin that creates a method a channel to communicate with the platform code. On the platform side, I have created a class that extends FlutterPlugin
However, when I run the app and Dart native code calls methods on the Android side using the method channel, I get Unhandled Exception: MissingPluginException.
Here's the code
Dart code
class GeofencePlugin {
final MethodChannel _channel =
const MethodChannel('marcel/geofencing_plugin');
Future<bool> init() async {
//callbackDispatcher is a top level function that acts as entry point for background isolate
final callback = PluginUtilities.getCallbackHandle(callbackDispatcher);
await _channel
.invokeMethod('GeofencingPlugin.initialiseService', <dynamic>[callback!.toRawHandle()]);
return true;
}
Future<bool> registerGeofence(GeofenceRegion region) async {
return true;
}
Future<bool> removeGeofence(GeofenceRegion region) async {
return true;
}
}
Android code
class GeofencingPlugin : ActivityAware, FlutterPlugin, MethodChannel.MethodCallHandler {
private var mContext : Context? = null
private var mActivity : Activity? = null
private val geofencePendingIntent: PendingIntent by lazy {
val intent = Intent(mContext, GeofenceBroadcastReceiver::class.java)
PendingIntent.getBroadcast(mContext, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)
}
companion object {
#JvmStatic
private val TAG = "MARK_TAG"
#JvmStatic
val SHARED_PREFERENCES_KEY = "com.example.flutter_playground.geofencing"
#JvmStatic
val CALLBACK_DISPATCHER_HANDLE_KEY = "callback_dispatch_handler"
#JvmStatic
private fun initialiseService(context: Context, args: ArrayList<*>?) {
val callbackHandle = args!![0] as Long
context.getSharedPreferences(SHARED_PREFERENCES_KEY, Context.MODE_PRIVATE)
.edit()
.putLong(CALLBACK_DISPATCHER_HANDLE_KEY, callbackHandle)
.commit()
}
}
override fun onAttachedToEngine(binding: FlutterPlugin.FlutterPluginBinding) {
mContext = binding.applicationContext
val channel = MethodChannel(binding.binaryMessenger, "marcel/geofencing_plugin")
channel.setMethodCallHandler(this)
}
override fun onDetachedFromEngine(binding: FlutterPlugin.FlutterPluginBinding) {
mContext = null
}
override fun onAttachedToActivity(binding: ActivityPluginBinding) {
mActivity = binding.activity
}
override fun onDetachedFromActivity() {
mActivity = null
}
override fun onDetachedFromActivityForConfigChanges() {
mActivity = null
}
override fun onReattachedToActivityForConfigChanges(binding: ActivityPluginBinding) {
mActivity = binding.activity
}
override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {
val args = call.arguments<ArrayList<*>>()
when(call.method) {
"GeofencingPlugin.initialiseService" -> {
initialiseService(mContext!!, args)
setupGeo()
result.success(true)
}
else -> result.notImplemented()
}
}
private fun setupGeo(){
val geofencingClient = mContext!!.getGeofenceClient()
val fence = Geofence.Builder()
.setRequestId("Mark")
.setCircularRegion(46.5422,14.4011,500f)
.setExpirationDuration(600000)
.setTransitionTypes(Geofence.GEOFENCE_TRANSITION_ENTER or Geofence.GEOFENCE_TRANSITION_EXIT)
.build()
val request = GeofencingRequest.Builder().apply {
setInitialTrigger(GeofencingRequest.INITIAL_TRIGGER_DWELL)
addGeofences(listOf(fence))
}.build()
geofencingClient.addGeofences(request, geofencePendingIntent)?.run {
addOnSuccessListener {
Toast.makeText(mContext,"Hahaha", Toast.LENGTH_LONG).show()
}
addOnFailureListener {
Log.d(TAG,it.message?:"Eoo")
Toast.makeText(mContext,"Heeerrrh", Toast.LENGTH_LONG).show()
}
}
}
}
I tried the following
Manually adding the android plugin class to the GeneratedPluginRegistrant.java file
Using flutterEngine.plugins.add('my plugin') in the MainActivity's onCreate method.

Answer 1

After digging into the pubsec.yaml of other plugins, I found out in order to have my app's plugin recognised by flutter I have to add the following to my pubsec.yaml under the flutter section:
plugin:
platforms:
android:
package: com.example.flutter_playground.geofencing
pluginClass: GeofencingPlugin