Migrate OnboardingViewModel to Flows

Fixes: b/186632953
Change-Id: I49aa5d2f0c48521b039c3883fc327c144c1abdcf

Author: Manuel Vivo

buildSrc/src/main/java/Libs.kt

@@ -63,6 +63,7 @@ object Libs {
     const val KOTLIN_STDLIB = "org.jetbrains.kotlin:kotlin-stdlib-jdk7"
     const val LIFECYCLE_COMPILER = "androidx.lifecycle:lifecycle-compiler"
     const val LIFECYCLE_LIVE_DATA_KTX = "androidx.lifecycle:lifecycle-livedata-ktx"
+    const val LIFECYCLE_RUNTIME_KTX = "androidx.lifecycle:lifecycle-runtime-ktx"
     const val LIFECYCLE_VIEW_MODEL_KTX = "androidx.lifecycle:lifecycle-viewmodel-ktx"
     const val LOTTIE = "com.airbnb.android:lottie"
     const val MATERIAL = "com.google.android.material:material"

depconstraints/build.gradle.kts

@@ -52,7 +52,7 @@ val hamcrest = "1.3"
 val hilt = Versions.HILT_AGP
 val junit = "4.13"
 val junitExt = "1.1.1"
-val lifecycle = "2.3.0"
+val lifecycle = "2.4.0-alpha01"
 val lottie = "3.0.0"
 val material = "1.3.0"
 val mockito = "3.3.1"
@@ -118,6 +118,7 @@ dependencies {
         api("${Libs.KOTLIN_STDLIB}:${Versions.KOTLIN}")
         api("${Libs.LIFECYCLE_COMPILER}:$lifecycle")
         api("${Libs.LIFECYCLE_LIVE_DATA_KTX}:$lifecycle")
+        api("${Libs.LIFECYCLE_RUNTIME_KTX}:$lifecycle")
         api("${Libs.LIFECYCLE_VIEW_MODEL_KTX}:$lifecycle")
         api("${Libs.LOTTIE}:$lottie")
         api("${Libs.MATERIAL}:$material")

mobile/build.gradle.kts

@@ -139,6 +139,11 @@ android {
         // Running lint over the debug variant is enough
         isCheckReleaseBuilds = false
         // See lint.xml for rules configuration
+
+        // TODO: Remove when upgrading lifecycle from `2.4.0-alpha01`.
+        // Fix: https://android-review.googlesource.com/c/platform/frameworks/support/+/1697465
+        // Bug: https://issuetracker.google.com/184830263
+        disable("NullSafeMutableLiveData")
     }
 
     testBuildType = "staging"
@@ -189,6 +194,7 @@ dependencies {
 
     // Architecture Components
     implementation(Libs.LIFECYCLE_LIVE_DATA_KTX)
+    implementation(Libs.LIFECYCLE_RUNTIME_KTX)
     kapt(Libs.LIFECYCLE_COMPILER)
     testImplementation(Libs.ARCH_TESTING)
     implementation(Libs.NAVIGATION_FRAGMENT_KTX)

mobile/src/main/java/com/google/samples/apps/iosched/ui/onboarding/OnboardingActivity.kt

@@ -22,12 +22,16 @@ import android.widget.FrameLayout
 import androidx.activity.viewModels
 import androidx.appcompat.app.AppCompatActivity
 import androidx.core.view.updatePadding
+import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.lifecycleScope
+import androidx.lifecycle.repeatOnLifecycle
 import com.google.samples.apps.iosched.R
-import com.google.samples.apps.iosched.shared.result.EventObserver
 import com.google.samples.apps.iosched.shared.util.inTransaction
 import com.google.samples.apps.iosched.ui.signin.SignInDialogFragment
 import com.google.samples.apps.iosched.util.doOnApplyWindowInsets
 import dagger.hilt.android.AndroidEntryPoint
+import kotlinx.coroutines.flow.collect
+import kotlinx.coroutines.launch
 
 @AndroidEntryPoint
 class OnboardingActivity : AppCompatActivity() {
@@ -56,12 +60,15 @@ class OnboardingActivity : AppCompatActivity() {
             }
         }
 
-        viewModel.navigateToSignInDialogAction.observe(
-            this,
-            EventObserver {
-                openSignInDialog()
+        lifecycleScope.launch {
+            lifecycle.repeatOnLifecycle(Lifecycle.State.STARTED) {
+                viewModel.navigationActions.collect { action ->
+                    if (action == OnboardingNavigationAction.NavigateToSignInDialog) {
+                        openSignInDialog()
+                    }
+                }
             }
-        )
+        }
     }
 
     private fun openSignInDialog() {

mobile/src/main/java/com/google/samples/apps/iosched/ui/onboarding/OnboardingFragment.kt

@@ -29,10 +29,11 @@ import androidx.fragment.app.FragmentManager
 import androidx.fragment.app.FragmentPagerAdapter
 import androidx.fragment.app.viewModels
 import com.google.samples.apps.iosched.databinding.FragmentOnboardingBinding
-import com.google.samples.apps.iosched.shared.result.EventObserver
 import com.google.samples.apps.iosched.shared.util.TimeUtils
 import com.google.samples.apps.iosched.ui.MainActivity
+import com.google.samples.apps.iosched.util.launchAndRepeatWithViewLifecycle
 import dagger.hilt.android.AndroidEntryPoint
+import kotlinx.coroutines.flow.collect
 
 private const val AUTO_ADVANCE_DELAY = 6_000L
 private const val INITIAL_ADVANCE_DELAY = 3_000L
@@ -64,7 +65,7 @@ class OnboardingFragment : Fragment() {
         inflater: LayoutInflater,
         container: ViewGroup?,
         savedInstanceState: Bundle?
-    ): View? {
+    ): View {
         binding = FragmentOnboardingBinding.inflate(inflater, container, false).apply {
             viewModel = onboardingViewModel
             lifecycleOwner = viewLifecycleOwner
@@ -76,18 +77,22 @@ class OnboardingFragment : Fragment() {
                 false
             }
         }
+        return binding.root
+    }
 
-        onboardingViewModel.navigateToMainActivity.observe(
-            viewLifecycleOwner,
-            EventObserver {
-                requireActivity().run {
-                    startActivity(Intent(this, MainActivity::class.java))
-                    finish()
+    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
+        super.onViewCreated(view, savedInstanceState)
+
+        launchAndRepeatWithViewLifecycle {
+            onboardingViewModel.navigationActions.collect { action ->
+                if (action == OnboardingNavigationAction.NavigateToMainScreen) {
+                    requireActivity().run {
+                        startActivity(Intent(this, MainActivity::class.java))
+                        finish()
+                    }
                 }
             }
-        )
-
-        return binding.root
+        }
     }
 
     override fun onAttach(context: Context) {

mobile/src/main/java/com/google/samples/apps/iosched/ui/onboarding/OnboardingSignInFragment.kt

@@ -36,7 +36,7 @@ class OnboardingSignInFragment : Fragment() {
         inflater: LayoutInflater,
         container: ViewGroup?,
         savedInstanceState: Bundle?
-    ): View? {
+    ): View {
         binding = FragmentOnboardingSigninBinding.inflate(inflater, container, false).apply {
             lifecycleOwner = viewLifecycleOwner
         }

mobile/src/main/java/com/google/samples/apps/iosched/ui/onboarding/OnboardingViewModel.kt

@@ -16,14 +16,14 @@
 
 package com.google.samples.apps.iosched.ui.onboarding
 
-import androidx.lifecycle.LiveData
-import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.google.samples.apps.iosched.shared.domain.prefs.OnboardingCompleteActionUseCase
-import com.google.samples.apps.iosched.shared.result.Event
+import com.google.samples.apps.iosched.shared.util.tryOffer
 import com.google.samples.apps.iosched.ui.signin.SignInViewModelDelegate
 import dagger.hilt.android.lifecycle.HiltViewModel
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.flow.receiveAsFlow
 import kotlinx.coroutines.launch
 import javax.inject.Inject
 
@@ -36,20 +36,25 @@ class OnboardingViewModel @Inject constructor(
     signInViewModelDelegate: SignInViewModelDelegate
 ) : ViewModel(), SignInViewModelDelegate by signInViewModelDelegate {
 
-    private val _navigateToMainActivity = MutableLiveData<Event<Unit>>()
-    val navigateToMainActivity: LiveData<Event<Unit>> = _navigateToMainActivity
-
-    private val _navigateToSignInDialogAction = MutableLiveData<Event<Unit>>()
-    val navigateToSignInDialogAction: LiveData<Event<Unit>> = _navigateToSignInDialogAction
+    private val _navigationActions = Channel<OnboardingNavigationAction>(Channel.CONFLATED)
+    // OnboardingViewModel is a shared ViewModel. Therefore, the navigation actions could be
+    // received by multiple collectors at the same time. With `receiveAsFlow`, we make sure only
+    // one collector will process the navigation event to avoid multiple back stack entries.
+    val navigationActions = _navigationActions.receiveAsFlow()
 
     fun getStartedClick() {
         viewModelScope.launch {
             onboardingCompleteActionUseCase(true)
-            _navigateToMainActivity.postValue(Event(Unit))
+            _navigationActions.send(OnboardingNavigationAction.NavigateToMainScreen)
         }
     }
 
     fun onSigninClicked() {
-        _navigateToSignInDialogAction.value = Event(Unit)
+        _navigationActions.tryOffer(OnboardingNavigationAction.NavigateToSignInDialog)
     }
 }
+
+sealed class OnboardingNavigationAction {
+    object NavigateToMainScreen : OnboardingNavigationAction()
+    object NavigateToSignInDialog : OnboardingNavigationAction()
+}

mobile/src/main/java/com/google/samples/apps/iosched/ui/onboarding/WelcomeDuringConferenceFragment.kt

@@ -40,7 +40,7 @@ class WelcomeDuringConferenceFragment : Fragment() {
         inflater: LayoutInflater,
         container: ViewGroup?,
         savedInstanceState: Bundle?
-    ): View? {
+    ): View {
         binding = FragmentOnboardingWelcomeDuringBinding.inflate(inflater, container, false).apply {
             lifecycleOwner = viewLifecycleOwner
         }

mobile/src/main/java/com/google/samples/apps/iosched/ui/onboarding/WelcomePreConferenceFragment.kt

@@ -40,7 +40,7 @@ class WelcomePreConferenceFragment : Fragment() {
         inflater: LayoutInflater,
         container: ViewGroup?,
         savedInstanceState: Bundle?
-    ): View? {
+    ): View {
         binding = FragmentOnboardingWelcomePreBinding.inflate(inflater, container, false).apply {
             lifecycleOwner = viewLifecycleOwner
         }

mobile/src/main/java/com/google/samples/apps/iosched/util/UiUtils.kt

@@ -20,7 +20,13 @@ import android.content.Context
 import android.graphics.drawable.Drawable
 import androidx.appcompat.content.res.AppCompatResources
 import androidx.core.graphics.drawable.DrawableCompat
+import androidx.fragment.app.Fragment
+import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.lifecycleScope
+import androidx.lifecycle.repeatOnLifecycle
 import com.google.samples.apps.iosched.R
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.launch
 
 fun navigationItemBackground(context: Context): Drawable? {
     // Need to inflate the drawable and CSL via AppCompatResources to work on Lollipop
@@ -44,3 +50,18 @@ fun navigationItemBackground(context: Context): Drawable? {
 fun slideOffsetToAlpha(value: Float, rangeMin: Float, rangeMax: Float): Float {
     return ((value - rangeMin) / (rangeMax - rangeMin)).coerceIn(0f, 1f)
 }
+
+/**
+ * Launches a new coroutine and repeats `block` every time the Fragment's viewLifecycleOwner
+ * is in and out of `minActiveState` lifecycle state.
+ */
+inline fun Fragment.launchAndRepeatWithViewLifecycle(
+    minActiveState: Lifecycle.State = Lifecycle.State.STARTED,
+    crossinline block: suspend CoroutineScope.() -> Unit
+) {
+    viewLifecycleOwner.lifecycleScope.launch {
+        viewLifecycleOwner.lifecycle.repeatOnLifecycle(minActiveState) {
+            block()
+        }
+    }
+}