[Formula Android] Add event listener to track performance.

formula-android-compose/src/main/java/com/instacart/formula/android/compose/ComposeViewFactory.kt

@@ -1,5 +1,6 @@
 package com.instacart.formula.android.compose
 
+import android.os.SystemClock
 import android.view.LayoutInflater
 import android.view.ViewGroup
 import androidx.compose.runtime.Composable
@@ -19,7 +20,13 @@ abstract class ComposeViewFactory<RenderModel> : ViewFactory<RenderModel> {
                 view.setContent {
                     val model = it.observable.subscribeAsState(null).value
                     if (model != null) {
+                        val start = SystemClock.uptimeMillis()
                         Content(model)
+                        val end = SystemClock.uptimeMillis()
+                        it.environment.eventListener?.onRendered(
+                            fragmentId = it.fragmentId,
+                            durationInMillis = end - start,
+                        )
                     }
                 }
                 null

formula-android/build.gradle

@@ -18,6 +18,12 @@ android {
         sourceCompatibility JavaVersion.VERSION_1_8
         targetCompatibility JavaVersion.VERSION_1_8
     }
+
+    testOptions {
+        unitTests {
+            returnDefaultValues true
+        }
+    }
 }
 
 tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {

formula-android/src/main/java/com/instacart/formula/FormulaAndroid.kt

@@ -22,21 +22,18 @@ object FormulaAndroid {
     /**
      * Initializes Formula Android integration. Should be called within [Application.onCreate].
      *
-     * @param logger A logger for debug Formula Android events.
-     * @param onFragmentError A global handler for fragment errors. Override this to log the crashes.
+     * @param fragmentEnvironment Environment model that configures various event listeners.
      */
     fun init(
         application: Application,
-        logger: ((String) -> Unit)? = null,
-        onFragmentError: (FragmentKey, Throwable) -> Unit = { _, it -> throw it },
+        fragmentEnvironment: FragmentEnvironment = FragmentEnvironment(),
         activities: ActivityConfigurator.() -> Unit
     ) {
         // Should we allow re-initialization?
         if (appManager != null) {
             throw IllegalStateException("can only initialize the store once.")
         }
 
-        val fragmentEnvironment = FragmentEnvironment(logger ?: {}, onFragmentError)
         val factory = ActivityStoreFactory(fragmentEnvironment, activities)
         val appManager = AppManager(factory)
         application.registerActivityLifecycleCallbacks(appManager)
@@ -47,6 +44,22 @@ object FormulaAndroid {
         FormulaFragmentDelegate.fragmentEnvironment = fragmentEnvironment
     }
 
+    /**
+     * Initializes Formula Android integration. Should be called within [Application.onCreate].
+     *
+     * @param logger A logger for debug Formula Android events.
+     * @param onFragmentError A global handler for fragment errors. Override this to log the crashes.
+     */
+    fun init(
+        application: Application,
+        logger: ((String) -> Unit)? = null,
+        onFragmentError: (FragmentKey, Throwable) -> Unit = { _, it -> throw it },
+        activities: ActivityConfigurator.() -> Unit
+    ) {
+        val fragmentEnvironment = FragmentEnvironment(logger ?: {}, onFragmentError)
+        init(application, fragmentEnvironment, activities)
+    }
+
     /**
      * Call this method in [FragmentActivity.onCreate] before calling [FragmentActivity.super.onCreate]
      */

formula-android/src/main/java/com/instacart/formula/android/FeatureView.kt

@@ -22,7 +22,8 @@ class FeatureView<RenderModel>(
     val lifecycleCallbacks: FragmentLifecycleCallback? = null,
 ) {
     class State<RenderModel>(
+        val fragmentId: FragmentId,
+        val environment: FragmentEnvironment,
         val observable: Observable<RenderModel>,
-        val onError: (Throwable) -> Unit,
     )
 }

formula-android/src/main/java/com/instacart/formula/android/FormulaFragment.kt

@@ -7,6 +7,7 @@ import android.view.ViewGroup
 import androidx.fragment.app.Fragment
 import com.instacart.formula.Cancelable
 import com.instacart.formula.android.internal.FormulaFragmentDelegate
+import com.instacart.formula.android.internal.getFormulaFragmentId
 import com.jakewharton.rxrelay3.BehaviorRelay
 
 class FormulaFragment : Fragment(), BaseFormulaFragment<Any> {
@@ -49,10 +50,9 @@ class FormulaFragment : Fragment(), BaseFormulaFragment<Any> {
         super.onViewCreated(view, savedInstanceState)
         featureView?.let { value ->
             val state = FeatureView.State(
+                fragmentId = getFormulaFragmentId(),
+                environment = FormulaFragmentDelegate.fragmentEnvironment(),
                 observable = stateRelay,
-                onError = {
-                    FormulaFragmentDelegate.logFragmentError(key, it)
-                }
             )
             cancelable = value.bind(state)
             this.lifecycleCallback = value.lifecycleCallbacks

formula-android/src/main/java/com/instacart/formula/android/FragmentEnvironment.kt

@@ -3,4 +3,27 @@ package com.instacart.formula.android
 data class FragmentEnvironment(
     val logger: (String) -> Unit = {},
     val onScreenError: (FragmentKey, Throwable) -> Unit = { _, it -> throw it },
-)
+    val eventListener: EventListener? = null,
+) {
+
+    /**
+     * Introspection API to track various formula fragment events and their performance.
+     */
+    interface EventListener {
+
+        /**
+         * Called after [FeatureFactory.initialize] is called.
+         */
+        fun onFeatureInitialized(fragmentId: FragmentId, durationInMillis: Long)
+
+        /**
+         * Called when [FormulaFragment] view is inflated.
+         */
+        fun onViewInflated(fragmentId: FragmentId, durationInMillis: Long)
+
+        /**
+         * Called after render model was applied to the [FeatureView].
+         */
+        fun onRendered(fragmentId: FragmentId, durationInMillis: Long)
+    }
+}

formula-android/src/main/java/com/instacart/formula/android/internal/FeatureBinding.kt

@@ -1,5 +1,6 @@
 package com.instacart.formula.android.internal
 
+import android.os.SystemClock
 import com.instacart.formula.Action
 import com.instacart.formula.Evaluation
 import com.instacart.formula.Formula
@@ -33,8 +34,14 @@ internal class FeatureBinding<in Component, in Dependencies, in Key : FragmentKe
                             Action.onData(fragmentId).onEvent {
                                 transition {
                                     try {
+                                        val start = SystemClock.uptimeMillis()
                                         val dependencies = toDependencies(input.component)
                                         val feature = feature.initialize(dependencies, key as Key)
+                                        val end = SystemClock.uptimeMillis()
+                                        input.environment.eventListener?.onFeatureInitialized(
+                                            fragmentId = fragmentId,
+                                            durationInMillis = end - start,
+                                        )
                                         input.onInitializeFeature(FeatureEvent.Init(fragmentId, feature))
                                     } catch (e: Exception) {
                                         input.onInitializeFeature(FeatureEvent.Failure(fragmentId, e))

formula-android/src/main/java/com/instacart/formula/android/internal/FormulaFragmentDelegate.kt

@@ -32,11 +32,7 @@ internal object FormulaFragmentDelegate {
     }
 
 
-    fun logFragmentError(key: FragmentKey, error: Throwable) {
-        fragmentEnvironment().onScreenError(key, error)
-    }
-
-    private fun fragmentEnvironment(): FragmentEnvironment {
+    fun fragmentEnvironment(): FragmentEnvironment {
         return checkNotNull(fragmentEnvironment) { "FormulaAndroid.init() not called." }
     }
 }

formula-android/src/main/java/com/instacart/formula/android/internal/FormulaFragmentViewFactory.kt

@@ -1,14 +1,17 @@
 package com.instacart.formula.android.internal
 
+import android.os.SystemClock
 import android.view.LayoutInflater
 import android.view.ViewGroup
 import com.instacart.formula.android.FeatureView
 import com.instacart.formula.android.ViewFactory
 import com.instacart.formula.android.FeatureEvent
+import com.instacart.formula.android.FragmentEnvironment
 import com.instacart.formula.android.FragmentId
 import java.lang.IllegalStateException
 
 internal class FormulaFragmentViewFactory(
+    private val environment: FragmentEnvironment,
     private val fragmentId: FragmentId,
     private val featureProvider: FeatureProvider,
 ) : ViewFactory<Any> {
@@ -17,6 +20,7 @@ internal class FormulaFragmentViewFactory(
 
     @Suppress("UNCHECKED_CAST")
     override fun create(inflater: LayoutInflater, container: ViewGroup?): FeatureView<Any> {
+        val start = SystemClock.uptimeMillis()
         val key = fragmentId.key
         val featureEvent = featureProvider.getFeature(fragmentId) ?: throw IllegalStateException("Could not find feature for $key.")
         val viewFactory = factory ?: when (featureEvent) {
@@ -31,6 +35,9 @@ internal class FormulaFragmentViewFactory(
             }
         }
         this.factory = viewFactory
-        return viewFactory.create(inflater, container)
+        val view = viewFactory.create(inflater, container)
+        val endTime = SystemClock.uptimeMillis()
+        environment.eventListener?.onViewInflated(fragmentId, endTime - start)
+        return view
     }
 }

formula-android/src/main/java/com/instacart/formula/android/internal/FragmentFlowRenderView.kt

@@ -142,7 +142,11 @@ internal class FragmentFlowRenderView(
 
     fun viewFactory(fragment: FormulaFragment): ViewFactory<Any> {
         initializeFragmentInstanceIdIfNeeded(fragment)
-        return FormulaFragmentViewFactory(fragment.getFormulaFragmentId(), featureProvider)
+        return FormulaFragmentViewFactory(
+            environment = fragmentEnvironment,
+            fragmentId = fragment.getFormulaFragmentId(),
+            featureProvider = featureProvider,
+        )
     }
 
     private fun notifyLifecycleStateChanged(fragment: Fragment, newState: Lifecycle.State) {

formula-android/src/main/java/com/instacart/formula/android/views/FeatureViewBindFunction.kt

@@ -1,5 +1,6 @@
 package com.instacart.formula.android.views
 
+import android.os.SystemClock
 import com.instacart.formula.Cancelable
 import com.instacart.formula.Renderer
 import com.instacart.formula.android.FeatureView
@@ -12,11 +13,18 @@ internal class FeatureViewBindFunction<RenderModel>(
     private val render: Renderer<RenderModel>
 ) : (FeatureView.State<RenderModel>) -> Cancelable? {
     override fun invoke(state: FeatureView.State<RenderModel>): Cancelable {
+        val environment = state.environment
         val disposable = state.observable.subscribe {
             try {
+                val start = SystemClock.uptimeMillis()
                 render(it)
+                val end = SystemClock.uptimeMillis()
+                environment.eventListener?.onRendered(
+                    fragmentId = state.fragmentId,
+                    durationInMillis = end - start,
+                )
             } catch (exception: Exception) {
-                state.onError(exception)
+                environment.onScreenError(state.fragmentId.key, exception)
             }
         }
         return Cancelable {