Improve lazy loading for Coil + OkHttp

This way, we can load Coil's backend on a background thread and not block the MainThread with it.
Previously, the Coil image loader was initialized with the first composed image, which caused ~10ms duration and most likely skipped frames.

Change-Id: Iaa583b6adc1df7d7a51dbae1473e539f2c0b0b62

app/src/main/java/com/google/samples/apps/nowinandroid/util/ImageLoaderAsyncFactory.kt

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.samples.apps.nowinandroid.util
+
+import androidx.tracing.trace
+import coil.ImageLoader
+import coil.ImageLoaderFactory
+import com.google.samples.apps.nowinandroid.core.network.di.ApplicationScope
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Deferred
+import kotlinx.coroutines.async
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
+import javax.inject.Inject
+
+/**
+ * This class asynchronously loads the Coil's image loader on a [ApplicationScope], which uses Default dispatcher.
+ * Reason for this is to prevent initializing Coil (and thus OkHttp internally) with the first image loading
+ * to prevent skipping frames and performance issues.
+ *
+ * Usage:
+ * - Init creates an async initialization of the image loader.
+ * - delegate to [newImageLoader] so that Coil can automatically reach for its loader.
+ */
+class ImageLoaderAsyncFactory @Inject constructor(
+    @ApplicationScope
+    appScope: CoroutineScope,
+    private val imageLoader: dagger.Lazy<ImageLoader>,
+) : ImageLoaderFactory {
+    private lateinit var asyncNewImageLoader: Deferred<ImageLoader>
+
+    init {
+        appScope.launch {
+            // Initializing asynchronously, but start immediately
+            asyncNewImageLoader = async { imageLoader.get() }
+        }
+    }
+
+    /**
+     * This runBlocking here is on purpose to prevent any unfinished Coil initialization.
+     * Most likely this will be already initialized by the time we want to show an image on the screen.
+     */
+    override fun newImageLoader() =
+        trace("NiaImageLoader.runBlocking") { runBlocking { asyncNewImageLoader.await() } }
+}

app/src/main/kotlin/com/google/samples/apps/nowinandroid/NiaApplication.kt

@@ -17,21 +17,20 @@
 package com.google.samples.apps.nowinandroid
 
 import android.app.Application
-import coil.ImageLoader
-import coil.ImageLoaderFactory
+import coil.Coil
 import com.google.samples.apps.nowinandroid.sync.initializers.Sync
+import com.google.samples.apps.nowinandroid.util.ImageLoaderAsyncFactory
 import com.google.samples.apps.nowinandroid.util.ProfileVerifierLogger
 import dagger.hilt.android.HiltAndroidApp
 import javax.inject.Inject
-import javax.inject.Provider
 
 /**
  * [Application] class for NiA
  */
 @HiltAndroidApp
-class NiaApplication : Application(), ImageLoaderFactory {
+class NiaApplication : Application() {
     @Inject
-    lateinit var imageLoader: Provider<ImageLoader>
+    lateinit var imageLoaderAsyncFactory: ImageLoaderAsyncFactory
 
     @Inject
     lateinit var profileVerifierLogger: ProfileVerifierLogger
@@ -41,7 +40,7 @@ class NiaApplication : Application(), ImageLoaderFactory {
         // Initialize Sync; the system responsible for keeping data in the app up to date.
         Sync.initialize(context = this)
         profileVerifierLogger()
+        // We set immediately Coil's image loader factory to prevent initialization with the first image.
+        Coil.setImageLoader(imageLoaderAsyncFactory)
     }
-
-    override fun newImageLoader(): ImageLoader = imageLoader.get()
 }

core/network/src/main/kotlin/com/google/samples/apps/nowinandroid/core/network/di/NetworkModule.kt

@@ -17,6 +17,7 @@
 package com.google.samples.apps.nowinandroid.core.network.di
 
 import android.content.Context
+import androidx.tracing.trace
 import coil.ImageLoader
 import coil.decode.SvgDecoder
 import coil.util.DebugLogger
@@ -51,7 +52,8 @@ internal object NetworkModule {
 
     @Provides
     @Singleton
-    fun okHttpCallFactory(): Call.Factory = OkHttpClient.Builder()
+    fun okHttpCallFactory(): Call.Factory = trace("NiaOkHttpClient") {
+        OkHttpClient.Builder()
             .addInterceptor(
                 HttpLoggingInterceptor()
                     .apply {
@@ -61,6 +63,7 @@ internal object NetworkModule {
                     },
             )
             .build()
+    }
 
     /**
      * Since we're displaying SVGs in the app, Coil needs an ImageLoader which supports this
@@ -72,13 +75,13 @@ internal object NetworkModule {
     @Provides
     @Singleton
     fun imageLoader(
-        okHttpCallFactory: Call.Factory,
+        // We specifically request dagger.Lazy here, so that it's not instantiated from Dagger.
+        okHttpCallFactory: dagger.Lazy<Call.Factory>,
         @ApplicationContext application: Context,
-    ): ImageLoader = ImageLoader.Builder(application)
-        .callFactory(okHttpCallFactory)
-        .components {
-            add(SvgDecoder.Factory())
-        }
+    ): ImageLoader = trace("NiaImageLoader") {
+        ImageLoader.Builder(application)
+            .callFactory { okHttpCallFactory.get() }
+            .components { add(SvgDecoder.Factory()) }
             // Assume most content images are versioned urls
             // but some problematic images are fetching each time
             .respectCacheHeaders(false)
@@ -89,3 +92,4 @@ internal object NetworkModule {
             }
             .build()
     }
+}