1. Adapt it to MVVM architecture

2. Add AuthStateListener and oberver to lisen the change of current login status
3. Solve the coordination between async operations

Author: butterflyforever

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

@@ -8,7 +8,11 @@ import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import androidx.fragment.app.activityViewModels
+import androidx.lifecycle.Observer
 import com.google.android.gms.common.SignInButton
+import com.google.samples.quickstart.canonical.SignInViewModel.Companion.FIREBASE_AUTH_WITH_GOOGLE_FAIL
+import com.google.samples.quickstart.canonical.SignInViewModel.Companion.FIREBASE_AUTH_WITH_GOOGLE_SUCCESSFUL
+import com.google.samples.quickstart.canonical.SignInViewModel.Companion.GOOGLE_SIGN_IN_UNSUCCESSFUL
 
 class LoginFragment : Fragment() {
 
@@ -41,6 +45,25 @@ class LoginFragment : Fragment() {
         // No other requestCode, ignore it.
     }
 
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        // Add login status change listener
+        signInVM.getFirebaseAuthLogStatusLiveData().observe(this, Observer {
+            when (it) {
+                true -> {
+                    Log.d(LOGIN_FRAGMENT_TAG, "firebaseUser is not null")
+                    val intent = Intent(context, MainActivity::class.java)
+                    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP)
+                    startActivity(intent)
+                }
+
+                false -> {
+                    Log.d(LOGIN_FRAGMENT_TAG, "firebaseUser is null")
+                }
+            }
+        })
+    }
+
     override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                               savedInstanceState: Bundle?): View? {
         // Inflate the layout for this fragment
@@ -56,9 +79,6 @@ class LoginFragment : Fragment() {
 
     companion object {
         const val RC_SIGN_IN = 0
-        const val GOOGLE_SIGN_IN_UNSUCCESSFUL = 1
-        const val FIREBASE_AUTH_WITH_GOOGLE_SUCCESSFUL = 2
-        const val FIREBASE_AUTH_WITH_GOOGLE_FAIL = 3
         const val LOGIN_FRAGMENT_TAG = "Login fragment"
     }
 }

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

@@ -3,15 +3,14 @@ package com.google.samples.quickstart.canonical
 import androidx.appcompat.app.AppCompatActivity
 import android.os.Bundle
 import android.util.Log
+import androidx.activity.viewModels
 import androidx.constraintlayout.widget.ConstraintLayout
 import androidx.fragment.app.FragmentTransaction
-import androidx.lifecycle.ViewModelProviders
 import com.google.android.material.bottomnavigation.BottomNavigationView
 
 class MainActivity : AppCompatActivity() {
 
-  private lateinit var signInVM : SignInViewModel
-
+  private val signInVM : SignInViewModel by viewModels()
 
   private fun setupNavigationBar() {
     supportFragmentManager
@@ -59,10 +58,8 @@ class MainActivity : AppCompatActivity() {
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     setContentView(R.layout.activity_main)
-
-    signInVM = ViewModelProviders.of(this)[SignInViewModel::class.java]
-    signInVM.signInInit(this, this)
-
+    Log.d(MAIN_ACTIVITY_TAG, "onCreate")
+    signInVM.signInVMInit(this, this)
     setupNavigationBar()
   }
 
@@ -76,8 +73,8 @@ class MainActivity : AppCompatActivity() {
 
       false -> {
         Log.d(MAIN_ACTIVITY_TAG, "No login. Update UI")
+//        signInVM.signInAccountInit()
         findViewById<ConstraintLayout>(R.id.main_activity_view).removeAllViews()
-
         supportFragmentManager
           .beginTransaction()
           .replace(R.id.main_activity_view, LoginFragment())
@@ -87,7 +84,6 @@ class MainActivity : AppCompatActivity() {
     }
   }
 
-
   companion object {
     const val MAIN_ACTIVITY_TAG = "MainActivity"
   }

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

@@ -119,7 +119,7 @@ class MapsFragment : Fragment() {
                 setPlacesSearchBias()
             } ?: run{
                 Log.d(FRAGMENT_TAG, "Locating Failed")
-                Toast.makeText(context, getString(R.string.cannot_access_location), Toast.LENGTH_LONG)
+                Toast.makeText(this.context, getString(R.string.cannot_access_location), Toast.LENGTH_LONG).show()
             }
         }
     }

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

@@ -10,18 +10,34 @@ import android.view.ViewGroup
 import android.widget.Button
 import android.widget.TextView
 import androidx.fragment.app.activityViewModels
+import androidx.lifecycle.Observer
 
-private const val ARG_PARAM1 = "param1"
-private const val ARG_PARAM2 = "param2"
 
-/**
- * A simple [Fragment] subclass.
- * Use the [MeFragment.newInstance] factory method to
- * create an instance of this fragment.
- */
 class MeFragment : Fragment() {
 
     private val signInVM: SignInViewModel by activityViewModels()
+    private lateinit var observer : Observer<Boolean>
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        // Add login status change listener
+        observer = Observer {
+            when (it) {
+                true -> {
+                    Log.d(ME_TAG, "firebaseUser is not null")
+                }
+
+                false -> {
+                    Log.d(ME_TAG, "firebaseUser is null")
+                    val intent = Intent(context, MainActivity::class.java)
+                    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP)
+                    startActivity(intent)
+                }
+            }
+        }
+        // set LifeCycle owner with MeFragment. Observe will be destroyed when MeFragment is destroyed
+        signInVM.getFirebaseAuthLogStatusLiveData().observe(this, observer)
+    }
 
     override fun onCreateView(
         inflater: LayoutInflater, container: ViewGroup?,
@@ -31,43 +47,18 @@ class MeFragment : Fragment() {
         return inflater.inflate(R.layout.fragment_me, container, false)
     }
 
-
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)
         val logoutButton : Button = view.findViewById(R.id.logout_button)
         logoutButton.setOnClickListener {
             // Sign out both Google account and Firebase
-            signInVM.signOut()?.addOnCompleteListener {
-                val intent = Intent(context, MainActivity::class.java)
-                intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP)
-                startActivity(intent)
-            }
+            signInVM.signOut()
         }
         // update UI
         view.findViewById<TextView>(R.id.textView)?.text = signInVM.getFirebaseAuthCurUser()?.email
     }
 
-
     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 MeFragment.
-         */
-
         private const val ME_TAG = "MeFragment"
-
-        // TODO: Rename and change types and number of parameters
-        @JvmStatic
-        fun newInstance(param1: String, param2: String) =
-            MeFragment().apply {
-                arguments = Bundle().apply {
-                    putString(ARG_PARAM1, param1)
-                    putString(ARG_PARAM2, param2)
-                }
-            }
     }
 }