1. Add login fragment. Seperate login process from MainActivity

2. Reduce unnecessary variables in MainActivity
3. Using ViewModel to save the user
4. Fix bug in firebaseAuthWithGoogle addOnCompleteListener
5. Remove the activity in backstack.

Author: butterflyforever

android/canonical/app/build.gradle

@@ -38,7 +38,7 @@ dependencies {
     implementation 'androidx.appcompat:appcompat:1.1.0'
     implementation "androidx.fragment:fragment-ktx:1.2.5"
     implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
-    implementation 'com.google.android.gms:play-services-auth:18.0.0'
+    implementation 'com.google.android.gms:play-services-auth:18.1.0'
     implementation 'com.google.android.material:material:1.1.0'
     implementation 'com.google.android.gms:play-services-maps:17.0.0'
     implementation 'com.google.android.gms:play-services-location:17.0.0'

android/canonical/app/src/main/java/com/google/samples/quickstart/canonical/LoginFragment.kt

@@ -0,0 +1,130 @@
+package com.google.samples.quickstart.canonical
+
+import android.content.Intent
+import android.os.Bundle
+import android.util.Log
+import androidx.fragment.app.Fragment
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import androidx.lifecycle.ViewModelProviders
+import com.google.android.gms.auth.api.signin.GoogleSignIn
+import com.google.android.gms.common.SignInButton
+import com.google.android.gms.common.api.ApiException
+import com.google.firebase.auth.GoogleAuthProvider
+
+// TODO: Rename parameter arguments, choose names that match
+// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
+private const val ARG_PARAM1 = "param1"
+private const val ARG_PARAM2 = "param2"
+
+/**
+ * A simple [Fragment] subclass.
+ * Use the [LoginFragment.newInstance] factory method to
+ * create an instance of this fragment.
+ */
+class LoginFragment : Fragment() {
+    // TODO: Rename and change types of parameters
+    private var param1: String? = null
+    private var param2: String? = null
+    private lateinit var signInVM : SignInViewModel
+
+    private fun signIn() {
+        val signInIntent = signInVM.getGoogleSignInClient().signInIntent
+        startActivityForResult(signInIntent, RC_SIGN_IN)
+    }
+
+    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
+        super.onActivityResult(requestCode, resultCode, data)
+
+        // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);
+        if (requestCode == RC_SIGN_IN) {
+            val task = GoogleSignIn.getSignedInAccountFromIntent(data)
+            if (task.isSuccessful) {
+                try {
+                    // Google Sign In was successful, authenticate with Firebase
+                    val account = task.getResult(ApiException::class.java)!!
+                    Log.d(TAG, "Google Sign In was successful:" + account.id)
+                    firebaseAuthWithGoogle(account.idToken!!)
+                    val intent = Intent(context, MainActivity::class.java)
+                    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP)
+                    startActivity(intent)
+                } catch (e: ApiException) {
+                    // Google Sign In failed
+                    Log.w(TAG, "Google sign in failed", e)
+                }
+            } else {
+                Log.w(TAG, "Google sign in unsuccessful")
+            }
+
+        }
+        // No other requestCode, ignore it.
+    }
+
+
+    private fun firebaseAuthWithGoogle(idToken: String) {
+        Log.d(TAG, "firebaseAuthWithGoogle start")
+        val credential = GoogleAuthProvider.getCredential(idToken, null)
+        Log.d(TAG, "firebaseAuthWithGoogle credential:$credential")
+        signInVM.getFirebaseAuth().signInWithCredential(credential)
+            .addOnCompleteListener { task ->
+                Log.d(TAG, "firebase firebaseAuthWithGoogle:task check")
+                if (task.isSuccessful) {
+                    // Firebase Sign in success, update UI with the signed-in user's information
+                    Log.d(TAG, "firebase signInWithCredential:success")
+                    val user = signInVM.getFirebaseAuth().currentUser
+                    Log.d(TAG, "firebase signed-in user's Email:" + user!!.email)
+                } else {
+                    // If sign in fails, log a message to the user.
+                    Log.w(TAG, "signInWithCredential:failure", task.exception)
+                }
+            }
+    }
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        arguments?.let {
+            param1 = it.getString(ARG_PARAM1)
+            param2 = it.getString(ARG_PARAM2)
+        }
+
+        signInVM = activity?.run {
+            ViewModelProviders.of(this)[SignInViewModel::class.java]
+        } ?: throw Exception("Null Activity")
+
+    }
+
+    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
+                              savedInstanceState: Bundle?): View? {
+        // Inflate the layout for this fragment
+        return inflater.inflate(R.layout.fragment_login, container, false)
+    }
+
+    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
+        super.onViewCreated(view, savedInstanceState)
+        view.findViewById<SignInButton>(R.id.sign_in_button).setOnClickListener {
+            signIn()
+        }
+    }
+
+    companion object {
+        /**
+         * Use this factory method to create a new instance of
+         * this fragment using the provided parameters.
+         *
+         * @param param1 Parameter 1.
+         * @param param2 Parameter 2.
+         * @return A new instance of fragment LoginFragment.
+         */
+        const val RC_SIGN_IN = 0
+        const val TAG = "Login fragment"
+        // TODO: Rename and change types and number of parameters
+        @JvmStatic fun newInstance(param1: String, param2: String) =
+                LoginFragment().apply {
+                    arguments = Bundle().apply {
+                        putString(ARG_PARAM1, param1)
+                        putString(ARG_PARAM2, param2)
+                    }
+                }
+    }
+}

android/canonical/app/src/main/java/com/google/samples/quickstart/canonical/MainActivity.kt

@@ -1,88 +1,23 @@
 package com.google.samples.quickstart.canonical
 
-import android.content.Intent
 import androidx.appcompat.app.AppCompatActivity
 import android.os.Bundle
 import android.util.Log
+import androidx.constraintlayout.widget.ConstraintLayout
 import androidx.fragment.app.FragmentTransaction
+import androidx.lifecycle.ViewModelProviders
 import com.google.android.gms.auth.api.signin.GoogleSignIn
-import com.google.android.gms.auth.api.signin.GoogleSignInClient
-import com.google.android.gms.auth.api.signin.GoogleSignInOptions
-import com.google.android.gms.common.SignInButton
-import com.google.android.gms.common.api.ApiException
 import com.google.android.material.bottomnavigation.BottomNavigationView
-import com.google.firebase.auth.FirebaseAuth
-import com.google.firebase.auth.GoogleAuthProvider
 
 class MainActivity : AppCompatActivity() {
-  lateinit var googleSignInClient: GoogleSignInClient
-  private lateinit var auth: FirebaseAuth
 
-  private fun googleSignInInit() {
-    val gso = GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
-      .requestIdToken(getString(R.string.default_web_client_id))
-      .requestEmail()
-      .build()
-
-    googleSignInClient = GoogleSignIn.getClient(this, gso)
-  }
-
-  private fun signIn() {
-    auth = FirebaseAuth.getInstance()
-    val signInIntent = googleSignInClient.signInIntent
-    startActivityForResult(signInIntent, RC_SIGN_IN)
-  }
-
-
-  override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
-    super.onActivityResult(requestCode, resultCode, data)
-
-    // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);
-    if (requestCode == RC_SIGN_IN) {
-      val task = GoogleSignIn.getSignedInAccountFromIntent(data)
-      if (task.isSuccessful) {
-        try {
-          // Google Sign In was successful, authenticate with Firebase
-          val account = task.getResult(ApiException::class.java)!!
-          Log.d(TAG, "firebaseAuthWithGoogle:" + account.id)
-          firebaseAuthWithGoogle(account.idToken!!)
-          setContentView(R.layout.activity_main)
-          setupNavigationBar()
-        } catch (e: ApiException) {
-          // Google Sign In failed
-          Log.w(TAG, "Google sign in failed", e)
-        }
-      } else {
-        Log.w(TAG, "Google sign in unsuccessful")
-      }
-
-    }
-    // No other requestCode, ignore it.
-  }
-
-
-  private fun firebaseAuthWithGoogle(idToken: String) {
-    val credential = GoogleAuthProvider.getCredential(idToken, null)
-    auth.signInWithCredential(credential)
-      .addOnCompleteListener(this) { task ->
-        if (task.isSuccessful) {
-          // Firebase Sign in success, update UI with the signed-in user's information
-          Log.d(FIREBASE_TAG, "signInWithCredential:success")
-          val user = auth.currentUser
-          Log.d(FIREBASE_TAG, "signed-in user's Email:" + user!!.email)
-        } else {
-          // If sign in fails, log a message to the user.
-          Log.w(FIREBASE_TAG, "signInWithCredential:failure", task.exception)
-        }
-      }
-  }
+  private lateinit var signInVM : SignInViewModel
 
 
   private fun setupNavigationBar() {
-    val runFragment = RunFragment()
     supportFragmentManager
       .beginTransaction()
-      .replace(R.id.fragment_container, runFragment)
+      .replace(R.id.fragment_container, RunFragment())
       .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
       .commit()
 
@@ -91,30 +26,28 @@ class MainActivity : AppCompatActivity() {
       when (item.itemId) {
 
         R.id.bottom_navigation_item_run -> {
-          val runFragment = RunFragment()
           supportFragmentManager
             .beginTransaction()
-            .replace(R.id.fragment_container, runFragment)
+            .replace(R.id.fragment_container, RunFragment())
             .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
             .commit()
           true
         }
 
         R.id.bottom_navigation_item_map -> {
-          val mapsFragment = MapsFragment()
+//          val mapsFragment = MapsFragment()
           supportFragmentManager
             .beginTransaction()
-            .replace(R.id.fragment_container, mapsFragment)
+            .replace(R.id.fragment_container, MapsFragment())
             .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
             .commit()
           true
         }
 
         R.id.bottom_navigation_item_profile -> {
-          val meFragment = MeFragment()
           supportFragmentManager
             .beginTransaction()
-            .replace(R.id.fragment_container, meFragment)
+            .replace(R.id.fragment_container, MeFragment())
             .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
             .commit()
           true
@@ -125,34 +58,37 @@ class MainActivity : AppCompatActivity() {
     }
   }
 
-
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     setContentView(R.layout.activity_main)
 
-    googleSignInInit()
-    setupNavigationBar()
+    signInVM = ViewModelProviders.of(this)[SignInViewModel::class.java]
+    signInVM.signInInit(this, this)
 
+    setupNavigationBar()
   }
 
-
   override fun onStart() {
     super.onStart()
+
     val account = GoogleSignIn.getLastSignedInAccount(this)
-    if (account == null) {
-      setContentView(R.layout.login_in_page)
-      findViewById<SignInButton>(R.id.sign_in_button).setOnClickListener {
-        signIn()
-      }
+    account?.let {
+      Log.d(TAG, "Already login")
+    } ?: run {
+      Log.d(TAG, "No login. Update UI")
+      findViewById<ConstraintLayout>(R.id.main_activity_view).removeAllViews()
+
+      supportFragmentManager
+        .beginTransaction()
+        .replace(R.id.main_activity_view, LoginFragment())
+        .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
+        .commit()
     }
   }
 
 
   companion object {
-    private const val RC_SIGN_IN = 0
-    private const val TAG = "MainActivity-Login"
-    private const val FIREBASE_TAG = "MainAct-firebase-Login"
+    private const val TAG = "MainActivity"
   }
 
-
 }

android/canonical/app/src/main/java/com/google/samples/quickstart/canonical/MeFragment.kt

@@ -9,13 +9,11 @@ import android.view.View
 import android.view.ViewGroup
 import android.widget.Button
 import android.widget.TextView
-import com.google.android.gms.auth.api.signin.GoogleSignIn
-import com.google.firebase.auth.FirebaseAuth
+import androidx.lifecycle.ViewModelProviders
 
 private const val ARG_PARAM1 = "param1"
 private const val ARG_PARAM2 = "param2"
 
-
 /**
  * A simple [Fragment] subclass.
  * Use the [MeFragment.newInstance] factory method to
@@ -25,13 +23,19 @@ class MeFragment : Fragment() {
     // TODO: Rename and change types of parameters
     private var param1: String? = null
     private var param2: String? = null
+    private lateinit var signInVM : SignInViewModel
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         arguments?.let {
             param1 = it.getString(ARG_PARAM1)
             param2 = it.getString(ARG_PARAM2)
         }
+
+        signInVM = activity?.run {
+            ViewModelProviders.of(this)[SignInViewModel::class.java]
+        } ?: throw Exception("Null Activity")
+
     }
 
 
@@ -49,24 +53,14 @@ class MeFragment : Fragment() {
         val logoutButton : Button = view.findViewById(R.id.logout_button)
         logoutButton.setOnClickListener {
             // Sign out both Google account and Firebase
-            FirebaseAuth.getInstance().signOut()
-            (activity as MainActivity).googleSignInClient.signOut().addOnCompleteListener {
+            signInVM.signOut()?.addOnCompleteListener {
                 val intent = Intent(context, MainActivity::class.java)
+                intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP)
                 startActivity(intent)
             }
         }
-    }
-
-
-    override fun onStart() {
-        super.onStart()
-        val account = GoogleSignIn.getLastSignedInAccount(this.context)
-        account?.let {
-            Log.i(ME_TAG, "Already login")
-            view?.findViewById<TextView>(R.id.textView)?.text = account.displayName
-        } ?.run {
-            Log.i(ME_TAG, "No login")
-        }
+        // update UI
+        view.findViewById<TextView>(R.id.textView)?.text = signInVM.getFirebaseAuth().currentUser?.email
     }