fix(api): JNI issues (#1509)

Author: dnys1

packages/amplify_api/android/src/main/kotlin/com/amazonaws/amplify/amplify_api/AmplifyApiPlugin.kt

@@ -15,7 +15,6 @@
 
 package com.amazonaws.amplify.amplify_api
 
-import android.content.Context
 import android.os.Handler
 import android.os.Looper
 import androidx.annotation.NonNull
@@ -42,15 +41,25 @@ import kotlinx.coroutines.Dispatchers
 /** AmplifyApiPlugin */
 class AmplifyApiPlugin : FlutterPlugin, MethodCallHandler {
 
-    private lateinit var channel: MethodChannel
-    private lateinit var eventchannel: EventChannel
-    private lateinit var context: Context
-    private val graphqlSubscriptionStreamHandler: GraphQLSubscriptionStreamHandler
+    private companion object {
+        /**
+         * API authorization providers configured during the `addPlugin` call.
+         *
+         * The auth providers require a reference to the active method channel to be able to
+         * communicate back to Dart code. If the app is moved to the background and resumed,
+         * the `Amplify.addPlugin` call does not re-configure auth providers, so these must
+         * be instantiated only once but still maintain a reference to the active method channel.
+         */
+        var flutterAuthProviders: FlutterAuthProviders? = null
+    }
+
+    private var channel: MethodChannel? = null
+    private var eventchannel: EventChannel? = null
+    private var graphqlSubscriptionStreamHandler: GraphQLSubscriptionStreamHandler? = null
     private val logger = Amplify.Logging.forNamespace("amplify:flutter:api")
     private var dispatcher: CoroutineDispatcher
 
     constructor() {
-        graphqlSubscriptionStreamHandler = GraphQLSubscriptionStreamHandler()
         dispatcher = Dispatchers.IO
     }
 
@@ -66,14 +75,14 @@ class AmplifyApiPlugin : FlutterPlugin, MethodCallHandler {
     private val handler = Handler(Looper.getMainLooper())
 
     override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
+        graphqlSubscriptionStreamHandler = graphqlSubscriptionStreamHandler ?: GraphQLSubscriptionStreamHandler()
         channel = MethodChannel(flutterPluginBinding.binaryMessenger, "com.amazonaws.amplify/api")
-        channel.setMethodCallHandler(this)
+        channel!!.setMethodCallHandler(this)
         eventchannel = EventChannel(
             flutterPluginBinding.binaryMessenger,
             "com.amazonaws.amplify/api_observe_events"
         )
-        eventchannel.setStreamHandler(graphqlSubscriptionStreamHandler)
-        context = flutterPluginBinding.applicationContext
+        eventchannel!!.setStreamHandler(graphqlSubscriptionStreamHandler)
     }
 
     @Suppress("UNCHECKED_CAST")
@@ -90,10 +99,14 @@ class AmplifyApiPlugin : FlutterPlugin, MethodCallHandler {
                 val authProvidersList: List<String> =
                     (arguments["authProviders"] as List<*>?)?.cast() ?: listOf()
                 val authProviders = authProvidersList.map { AuthorizationType.valueOf(it) }
+                if (flutterAuthProviders == null) {
+                    flutterAuthProviders = FlutterAuthProviders(authProviders)
+                }
+                flutterAuthProviders!!.setMethodChannel(channel)
                 Amplify.addPlugin(
                     AWSApiPlugin
                         .builder()
-                        .apiAuthProviders(FlutterAuthProviders(authProviders, channel).factory)
+                        .apiAuthProviders(flutterAuthProviders!!.factory)
                         .build()
                 )
                 logger.info("Added API plugin")
@@ -119,7 +132,7 @@ class AmplifyApiPlugin : FlutterPlugin, MethodCallHandler {
                 "subscribe" -> FlutterGraphQLApi(dispatcher).subscribe(
                     result,
                     arguments,
-                    graphqlSubscriptionStreamHandler
+                    graphqlSubscriptionStreamHandler!!
                 )
                 else -> result.notImplemented()
             }
@@ -149,7 +162,13 @@ class AmplifyApiPlugin : FlutterPlugin, MethodCallHandler {
         }
     }
 
-    override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {
-        channel.setMethodCallHandler(null)
+    override fun onDetachedFromEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
+        flutterAuthProviders?.setMethodChannel(null)
+        channel?.setMethodCallHandler(null)
+        channel = null
+        eventchannel?.setStreamHandler(null)
+        eventchannel = null
+        graphqlSubscriptionStreamHandler?.close()
+        graphqlSubscriptionStreamHandler = null
     }
 }

packages/amplify_api/android/src/main/kotlin/com/amazonaws/amplify/amplify_api/GraphQLSubscriptionStreamHandler.kt

@@ -32,6 +32,10 @@ class GraphQLSubscriptionStreamHandler : EventChannel.StreamHandler {
         eventSink = null
     }
 
+    fun close() {
+        eventSink?.endOfStream()
+    }
+
     fun sendEvent(payload: Map<String, Any>?, id: String, type: GraphQLSubscriptionEventTypes) {
         handler.post {
             val result: MutableMap<String, Any?> = mutableMapOf(

packages/amplify_api/android/src/main/kotlin/com/amazonaws/amplify/amplify_api/auth/FlutterAuthProvider.kt

@@ -29,10 +29,8 @@ import kotlinx.coroutines.*
  * Manages the shared state of all [FlutterAuthProvider] instances.
  */
 class FlutterAuthProviders(
-    private val authProviders: List<AuthorizationType>,
-    private val methodChannel: MethodChannel
+    private val authProviders: List<AuthorizationType>
 ) {
-
     private companion object {
         /**
          * Timeout on a single [getToken] call.
@@ -50,6 +48,19 @@ class FlutterAuthProviders(
         val coroutineName = CoroutineName(tag)
     }
 
+    /**
+     * The method channel used for Android -> Flutter communication. Should be cleared when the API
+     * plugin is detached from Flutter and set when it is reattached.
+     */
+    private var methodChannel: MethodChannel? = null
+
+    /**
+     * Configures the method channel for API authorization.
+     */
+    fun setMethodChannel(methodChannel: MethodChannel?) {
+        this.methodChannel = methodChannel
+    }
+
     /**
      * A factory of [FlutterAuthProvider] instances.
      */
@@ -74,7 +85,7 @@ class FlutterAuthProviders(
     fun getToken(authType: AuthorizationType): String? {
         // Not blocking the main thread is required for making platform channel calls without
         // deadlock.
-        if (Thread.currentThread() == Looper.getMainLooper().thread) {
+        if (Thread.currentThread() == Looper.getMainLooper().thread || methodChannel == null) {
             Log.e(tag, ExceptionMessages.createGithubIssueString)
             return null
         }
@@ -93,7 +104,7 @@ class FlutterAuthProviders(
                     }
 
                     override fun error(
-                        errorCode: String?,
+                        errorCode: String,
                         errorMessage: String?,
                         errorDetails: Any?
                     ) {
@@ -109,7 +120,7 @@ class FlutterAuthProviders(
                     }
                 }
                 launch(Dispatchers.Main) {
-                    methodChannel.invokeMethod(
+                    methodChannel!!.invokeMethod(
                         "getLatestAuthToken",
                         authType.name,
                         result
@@ -152,4 +163,4 @@ class FlutterAuthProvider(
 
     override fun getLatestAuthToken(): String =
         provider.getToken(type) ?: throw noTokenAvailable(type)
-}
+}