title: Error Flutter Firebase Auth and Google Sign In
body: <p>I have 2 flutter apps as my learning. Both of them using firebase auth and google sign in with exact same code. I manage to copy this snippet from this <a href="https://fireship.io/lessons/flutter-firebase-google-oauth-firestore/" rel="nofollow noreferrer">url</a>
  But have different firebase app.</p>
  
  <p>First App is completely run well. but the second one is kind of misterious.
  I do not know why I getting this error</p>
  
  <pre><code>E/MethodChannel#plugins.flutter.io/firebase_auth( 9042): Failed to handle method call
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042): java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.firebase.auth.FirebaseAuth.addAuthStateListener(com.google.firebase.auth.FirebaseAuth$AuthStateListener)' on a null object reference
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at io.flutter.plugins.firebaseauth.FirebaseAuthPlugin.handleStartListeningAuthState(FirebaseAuthPlugin.java:629)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at io.flutter.plugins.firebaseauth.FirebaseAuthPlugin.onMethodCall(FirebaseAuthPlugin.java:149)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:201)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:88)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:219)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at android.os.MessageQueue.nativePollOnce(Native Method)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at android.os.MessageQueue.next(MessageQueue.java:326)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at android.os.Looper.loop(Looper.java:160)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at android.app.ActivityThread.main(ActivityThread.java:6669)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at java.lang.reflect.Method.invoke(Native Method)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
  E/MethodChannel#plugins.flutter.io/firebase_auth( 9042):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
  D/EGL_emulation( 9042): eglMakeCurrent: 0xc9976640: ver 2 0 (tinfo 0xe1031ea0)
  E/flutter ( 9042): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: PlatformException(error, Attempt to invoke virtual method 'void com.google.firebase.auth.FirebaseAuth.addAuthStateListener(com.google.firebase.auth.FirebaseAuth$AuthStateListener)' on a null object reference, null)
  </code></pre>
  
  <p>and this error when I signing in with google sign in.</p>
  
  <pre><code>E/MethodChannel#plugins.flutter.io/google_sign_in( 9042): Failed to handle method call
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042): android.content.ActivityNotFoundException: Unable to find explicit activity class {com.example.tokoku_flutter/com.google.android.gms.auth.api.signin.internal.SignInHubActivity}; have you declared this activity in your AndroidManifest.xml?
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at android.app.Instrumentation.checkStartActivityResult(Instrumentation.java:2005)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at android.app.Instrumentation.execStartActivity(Instrumentation.java:1673)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at android.app.Activity.startActivityForResult(Activity.java:4586)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at android.app.Activity.startActivityForResult(Activity.java:4544)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at io.flutter.plugins.googlesignin.GoogleSignInPlugin$Delegate.signIn(GoogleSignInPlugin.java:292)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at io.flutter.plugins.googlesignin.GoogleSignInPlugin.onMethodCall(GoogleSignInPlugin.java:77)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:201)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:88)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:219)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at android.os.MessageQueue.nativePollOnce(Native Method)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at android.os.MessageQueue.next(MessageQueue.java:326)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at android.os.Looper.loop(Looper.java:160)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at android.app.ActivityThread.main(ActivityThread.java:6669)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at java.lang.reflect.Method.invoke(Native Method)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
  E/MethodChannel#plugins.flutter.io/google_sign_in( 9042):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
  D/AndroidRuntime( 9042): Shutting down VM
  E/AndroidRuntime( 9042): FATAL EXCEPTION: main
  E/AndroidRuntime( 9042): Process: com.example.tokoku_flutter, PID: 9042
  E/AndroidRuntime( 9042): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=53293, result=0, data=null} to activity {com.example.tokoku_flutter/com.example.tokoku_flutter.MainActivity}: java.lang.IllegalStateException: Reply already submitted
  E/AndroidRuntime( 9042):    at android.app.ActivityThread.deliverResults(ActivityThread.java:4360)
  E/AndroidRuntime( 9042):    at android.app.ActivityThread.handleSendResult(ActivityThread.java:4402)
  E/AndroidRuntime( 9042):    at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:49)
  E/AndroidRuntime( 9042):    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
  E/AndroidRuntime( 9042):    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
  E/AndroidRuntime( 9042):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
  E/AndroidRuntime( 9042):    at android.os.Handler.dispatchMessage(Handler.java:106)
  E/AndroidRuntime( 9042):    at android.os.Looper.loop(Looper.java:193)
  E/AndroidRuntime( 9042):    at android.app.ActivityThread.main(ActivityThread.java:6669)
  E/AndroidRuntime( 9042):    at java.lang.reflect.Method.invoke(Native Method)
  E/AndroidRuntime( 9042):    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
  E/AndroidRuntime( 9042):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
  E/AndroidRuntime( 9042): Caused by: java.lang.IllegalStateException: Reply already submitted
  E/AndroidRuntime( 9042):    at io.flutter.embedding.engine.dart.DartMessenger$Reply.reply(DartMessenger.java:124)
  E/AndroidRuntime( 9042):    at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler$1.error(MethodChannel.java:209)
  E/AndroidRuntime( 9042):    at io.flutter.plugins.googlesignin.GoogleSignInPlugin$Delegate.finishWithError(GoogleSignInPlugin.java:386)
  E/AndroidRuntime( 9042):    at io.flutter.plugins.googlesignin.GoogleSignInPlugin$Delegate.onActivityResult(GoogleSignInPlugin.java:524)
  E/AndroidRuntime( 9042):    at io.flutter.app.FlutterPluginRegistry.onActivityResult(FlutterPluginRegistry.java:222)
  E/AndroidRuntime( 9042):    at io.flutter.app.FlutterActivityDelegate.onActivityResult(FlutterActivityDelegate.java:142)
  E/AndroidRuntime( 9042):    at io.flutter.app.FlutterActivity.onActivityResult(FlutterActivity.java:142)
  E/AndroidRuntime( 9042):    at android.app.Activity.dispatchActivityResult(Activity.java:7454)
  E/AndroidRuntime( 9042):    at android.app.ActivityThread.deliverResults(ActivityThread.java:4353)
  E/AndroidRuntime( 9042):    ... 11 more
  E/flutter ( 9042): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: PlatformException(error, Unable to find explicit activity class {com.example.tokoku_flutter/com.google.android.gms.auth.api.signin.internal.SignInHubActivity}; have you declared this activity in your AndroidManifest.xml?, null)
  E/flutter ( 9042): #0      StandardMethodCodec.decodeEnvelope 
  package:flutter/…/services/message_codecs.dart:564
  E/flutter ( 9042): #1      MethodChannel.invokeMethod 
  package:flutter/…/services/platform_channel.dart:302
  E/flutter ( 9042): &lt;asynchronous suspension&gt;
  E/flutter ( 9042): #2      GoogleSignIn._callMethod 
  package:google_sign_in/google_sign_in.dart:226
  E/flutter ( 9042): &lt;asynchronous suspension&gt;
  E/flutter ( 9042): #3      GoogleSignIn._addMethodCall 
  package:google_sign_in/google_sign_in.dart:268
  E/flutter ( 9042): #4      GoogleSignIn.signIn 
  package:google_sign_in/google_sign_in.dart:339
  E/flutter ( 9042): #5      AuthService.googleSignIn 
  package:tokoku_flutter/services/AuthService.dart:39
  E/flutter ( 9042): &lt;asynchronous suspension&gt;
  E/flutter ( 9042): #6      _LoginPageState._loginButton.&lt;anonymous closure&gt;.&lt;anonymous closure&gt; 
  package:tokoku_flutter/pages/LoginPage.dart:60
  E/flutter ( 9042): #7      _InkResponseState._handleTap 
  package:flutter/…/material/ink_well.dart:511
  E/flutter ( 9042): #8      _InkResponseState.build.&lt;anonymous closure&gt; 
  package:flutter/…/material/ink_well.dart:566
  E/flutter ( 9042): #9      GestureRecognizer.invokeCallback 
  package:flutter/…/gestures/recognizer.dart:166
  E/flutter ( 9042): #10     TapGestureRecognizer._checkUp 
  package:flutter/…/gestures/tap.dart:240
  E/flutter ( 9042): #11     TapGestureRecognizer.handlePrimaryPointer 
  package:flutter/…/gestures/tap.dart:177
  E/flutter ( 9042): #12     PrimaryPointerGestureRecognizer.handleEvent 
  package:flutter/…/gestures/recognizer.dart:436
  E/flutter ( 9042): #13     PointerRouter._dispatch 
  package:flutter/…/gestures/pointer_router.dart:73
  E/flutter ( 9042): #14     PointerRouter.route 
  package:flutter/…/gestures/pointer_router.dart:101
  E/flutter ( 9042): #15     _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding.handleEvent 
  package:flutter/…/gestures/binding.dart:221
  E/flutter ( 9042): #16     _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding.dispatchEvent 
  package:flutter/…/gestures/binding.dart:199
  E/flutter ( 9042): #17     _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding._handlePointerEvent 
  package:flutter/…/gestures/binding.dart:156
  E/flutter ( 9042): #18     _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding._flushPointerEventQueue 
  package:flutter/…/gestures/binding.dart:102
  E/flutter ( 9042): #19     _WidgetsFlutterBinding&amp;BindingBase&amp;GestureBinding._handlePointerDataPacket 
  package:flutter/…/gestures/binding.dart:86
  E/flutter ( 9042): #20     _rootRunUnary  (dart:async/zone.dart:1136:13)
  E/flutter ( 9042): #21     _CustomZone.runUnary  (dart:async/zone.dart:1029:19)
  E/flutter ( 9042): #22     _CustomZone.runUnaryGuarded  (dart:async/zone.dart:931:7)
  E/flutter ( 9042): #23     _invoke1  (dart:ui/hooks.dart:233:10)
  E/flutter ( 9042): #24     _dispatchPointerDataPacket  (dart:ui/hooks.dart:154:5)
  E/flutter ( 9042):
  I/Process ( 9042): Sending signal. PID: 9042 SIG: 9
  Lost connection to device.
  Exited (sigterm)
  </code></pre>
  
  <p>after tap the sign in button, my app is closed.</p>
  
  <p>here my dependencies i use:</p>
  
  <pre><code>dependencies:
    flutter:
      sdk: flutter
  
    # The following adds the Cupertino Icons font to your application.
    # Use with the CupertinoIcons class for iOS style icons.
    cupertino_icons: ^0.1.2
    rxdart: ^0.22.0
    firebase_auth: ^0.11.1
    firebase_core: ^0.4.0+1
    google_sign_in: ^4.0.1+3
    cloud_firestore: ^0.11.0+2
    get_it: ^1.0.3
  </code></pre>
  
  <p>NB:
  I already set my sha key in my firebase app.
  I already put the googleservice.json
  I already add classpath and dependencies in gradle
  I already migrate my flutter app to androidX</p>