Fixed bug where a method was being called on the parameter of the constructor and not the instance variable causing it to sometimes call on null

lib/src/resources/authService.dart

@@ -8,6 +8,8 @@ import '../models/summary_model.dart';
 import '../models/user_model.dart';
 
 class AuthService {
+  final _googleSignInProvider = GoogleSignInProvider();
+  final _firestoreProvider = FirestoreProvider();
   final _user = BehaviorSubject<FirebaseUser>();
 
   Observable<FirebaseUser> get userStream => _user.stream;
@@ -16,9 +18,6 @@ class AuthService {
     _googleSignInProvider.onAuthStateChange.pipe(_user);
   }
 
-  final _googleSignInProvider = GoogleSignInProvider();
-  final _firestoreProvider = FirestoreProvider();
-
   Future<void> googleLoginAndSignup() async {
     final user = await _googleSignInProvider.signIn();
 

lib/src/resources/firestore_provider.dart

@@ -16,7 +16,7 @@ class FirestoreProvider {
 
   FirestoreProvider([Firestore firestore])
       : _firestore = firestore ?? Firestore.instance {
-    firestore.settings(timestampsInSnapshotsEnabled: true);
+    _firestore.settings(timestampsInSnapshotsEnabled: true);
   }
   //-----------------------User related operations------------------------------
 

lib/src/screens/login_screen.dart

@@ -1,10 +1,13 @@
 import 'package:flutter/material.dart';
 import 'package:font_awesome_flutter/font_awesome_flutter.dart';
 
+import '../resources/authService.dart';
 import '../widgets/logo.dart';
 import '../widgets/gradient_button.dart';
 
 class LoginScreen extends StatelessWidget {
+  final AuthService _authService = authService;
+
   Widget build(BuildContext context) {
     return Scaffold(
       body: Container(
@@ -20,6 +23,7 @@ class LoginScreen extends StatelessWidget {
             Expanded(
               child: Center(
                 child: GradientButton(
+                  onTap: _authService.googleLoginAndSignup(),
                   height: 50,
                   width: 310,
                   radius: 25,

lib/src/widgets/gradient_button.dart

@@ -7,7 +7,7 @@ class GradientButton extends StatelessWidget {
   final Widget child;
   final double height;
   final double width;
-  final VoidCallback onTap;
+  final onTap;
   GradientButton({
     this.radius = 4,
     @required this.child,